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  • 801.
    Singh, Nishant K.
    et al.
    Max Planck Inst Solar Syst Res, Gottingen, Germany..
    Raichur, Harsha
    Max Planck Inst Solar Syst Res, Gottingen, Germany..
    Kapyla, Maarit J.
    Max Planck Inst Solar Syst Res, Gottingen, Germany.;Aalto Univ, ReSoLVE Ctr Excellence, Dept Comp Sci, Aalto, Finland..
    Rheinhardt, Matthias
    Aalto Univ, ReSoLVE Ctr Excellence, Dept Comp Sci, Aalto, Finland..
    Brandenburg, Axel
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Stockholm, Sweden.;Stockholm Univ, AlbaNova Univ Ctr, Dept Astron, Stockholm, Sweden.;Univ Colorado, JILA, Boulder, CO 80309 USA.;Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA.;Lab Atmospher & Space Phys, Boulder, CO USA..
    Kapyla, Petri J.
    Stockholm Univ, AlbaNova Univ Ctr, Dept Astron, Stockholm, Sweden.;Georg August Univ Gottingen, Inst Astrophys, Gottingen, Germany..
    f-mode strengthening from a localised bipolar subsurface magnetic field2019Inngår i: Geophysical and Astrophysical Fluid Dynamics, ISSN 0309-1929, E-ISSN 1029-0419Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent numerical work in helioseismology has shown that a periodically varying subsurface magnetic field leads to a fanning of the f-mode, which emerges from a density jump at the surface. In an attempt to model a more realistic situation, we now modulate this periodic variation with an envelope, giving thus more emphasis on localised bipolar magnetic structures in the middle of the domain. Some notable findings are: (i) compared to the purely hydrodynamic case, the strength of the f-mode is significantly larger at high horizontal wavenumbers k, but the fanning is weaker for the localised subsurface magnetic field concentrations investigated here than the periodic ones studied earlier; (ii) when the strength of the magnetic field is enhanced at a fixed depth below the surface, the fanning of the f-mode in the diagram increases proportionally in such a way that the normalised f-mode strengths remain nearly the same in different such cases; (iii) the unstable Bloch modes reported previously in case of harmonically varying magnetic fields are now completely absent when more realistic localised magnetic field concentrations are imposed beneath the surface, thus suggesting that the Bloch modes are unlikely to be supported during most phases of the solar cycle; (iv) the f-mode strength appears to depend also on the depth of magnetic field concentrations such that it shows a relative decrement when the maximum of the magnetic field is moved to a deeper layer. We argue that detections of f-mode perturbations such as those being explored here could be effective tracers of solar magnetic fields below the photosphere before these are directly detectable as visible manifestations in terms of active regions or sunspots.

  • 802. Sitarek, J.
    et al.
    González, J. B.
    Ramazani, V. F.
    Lindfors, E.
    Pedaletti, G.
    Tavecchio, F.
    Acosta, M. V.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Baliyan, K.
    Kaur, N.
    Sameer,
    Jorstad, S.
    Raiteri, C.
    Collaborations, MAGIC and Fermi-LAT
    MAGIC observations of variable very-high-energy gamma-ray emission from PKS1510-089 during May 2015 outburst2017Inngår i: Proceedings of Science, Sissa Medialab Srl , 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    PKS1510-089 is a flat spectrum radio quasar located at a redshift of 0.36. It is one of only a few such sources detected in very-high-energy (VHE, >100 GeV) gamma rays. Though PKS1510-089 is highly variable at GeV energies, until recently no variability has been observed in the VHE band. In 2015 May PKS1510-089 showed a high state in optical and in the GeV range. A VHE gamma-ray flare was detected with MAGIC at that time, showing the first instance of VHE gamma-ray flux variability on the time scale of days in this source. We will present the MAGIC results from this observation, discuss their temporal and spectral properties in the multi-wavelength context and present modelling of such emission in the external Compton scenario. 

  • 803. Slapak, Rikard
    et al.
    Hamrin, Maria
    Pitkanen, Timo
    Yamauchi, Masatoshi
    Nilsson, Hans
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Schillings, Audrey
    Quantification of the total ion transport in the near-Earth plasma sheet2017Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 35, nr 4, s. 869-877Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent studies strongly suggest that a majority of the observed O+ cusp outflows will eventually escape into the solar wind, rather than be transported to the plasma sheet. Therefore, an investigation of plasma sheet flows will add to these studies and give a more complete picture of magnetospheric ion dynamics. Specifically, it will provide a greater understanding of atmospheric loss. We have used Cluster spacecraft 4 to quantify the H+ and O+ total transports in the near-Earth plasma sheet, using data covering 2001-2005. The results show that both H+ and O+ have earthward net fluxes of the orders of 1026 and 1024 s(-1), respectively. The O+ plasma sheet return flux is 1 order of magnitude smaller than the O+ outflows observed in the cusps, strengthening the view that most ionospheric O+ outflows do escape. The H+ return flux is approximately the same as the ionospheric outflow, suggesting a stable budget of H+ in the magnetosphere. However, low-energy H+, not detectable by the ion spectrometer, is not considered in our study, leaving the complete magnetospheric H+ circulation an open question. Studying tailward flows separately reveals a total tailward O+ flux of about 0 : 5 x w10(25)s(-1), which can be considered as a lower limit of the nightside auroral region O+ outflow. Lower velocity flows (< 100 km s(-1)) contribute most to the total transports, whereas the high-velocity flows contribute very little, suggesting that bursty bulk flows are not dominant in plasma sheet mass transport.

  • 804. Soffitta, Paolo
    et al.
    Barcons, Xavier
    Bellazzini, Ronaldo
    Braga, Joao
    Costa, Enrico
    Fraser, George W.
    Gburek, Szymon
    Huovelin, Juhani
    Matt, Giorgio
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Poutanen, Juri
    Reglero, Victor
    Santangelo, Andrea
    Sunyaev, Rashid A.
    Tagliaferri, Gianpiero
    Weisskopf, Martin
    Aloisio, Roberto
    Amato, Elena
    Attina, Primo
    Axelsson, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Baldini, Luca
    Basso, Stefano
    Bianchi, Stefano
    Blasi, Pasquale
    Bregeon, Johan
    Brez, Alessandro
    Bucciantini, Niccolo
    Burderi, Luciano
    Burwitz, Vadim
    Casella, Piergiorgio
    Churazov, Eugene
    Civitani, Marta
    Covino, Stefano
    Curado da Silva, Rui Miguel
    Cusumano, Giancarlo
    Dadina, Mauro
    D'Amico, Flavio
    De Rosa, Alessandra
    Di Cosimo, Sergio
    Di Persio, Giuseppe
    Di Salvo, Tiziana
    Dovciak, Michal
    Elsner, Ronald
    Eyles, Chris J.
    Fabian, Andrew C.
    Fabiani, Sergio
    Feng, Hua
    Giarrusso, Salvatore
    Goosmann, Rene W.
    Grandi, Paola
    Grosso, Nicolas
    Israel, Gianluca
    Jackson, Miranda
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Kaaret, Philip
    Karas, Vladimir
    Kuss, Michael
    Lai, Dong
    La Rosa, Giovanni
    Larsson, Josefin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Larsson, Stefan
    Latronico, Luca
    Maggio, Antonio
    Maia, Jorge
    Marin, Frederic
    Massai, Marco Maria
    Mineo, Teresa
    Minuti, Massimo
    Moretti, Elena
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Muleri, Fabio
    O'Dell, Stephen L.
    Pareschi, Giovanni
    Peres, Giovanni
    Pesce, Melissa
    Petrucci, Pierre-Olivier
    Pinchera, Michele
    Porquet, Delphine
    Ramsey, Brian
    Rea, Nanda
    Reale, Fabio
    Rodrigo, Juana Maria
    Rozanska, Agata
    Rubini, Alda
    Rudawy, Pawel
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Salvati, Marco
    de Santiago, Valdivino Alexandre, Jr.
    Sazonov, Sergey
    Sgro, Carmelo
    Silver, Eric
    Spandre, Gloria
    Spiga, Daniele
    Stella, Luigi
    Tamagawa, Toru
    Tamborra, Francesco
    Tavecchio, Fabrizio
    Dias, Teresa Teixeira
    van Adelsberg, Matthew
    Wu, Kinwah
    Zane, Silvia
    XIPE: the X-ray imaging polarimetry explorer2013Inngår i: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 36, nr 3, s. 523-567Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017. The proposal was, unfortunately, not selected. To be compliant with this schedule, we designed the payload mostly with existing items. The XIPE proposal takes advantage of the completed phase A of POLARIX for an ASI small mission program that was cancelled, but is different in many aspects: the detectors, the presence of a solar flare polarimeter and photometer and the use of a light platform derived by a mass production for a cluster of satellites. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus. Two additional GPDs filled with a 3-bar Ar-DME mixture always face the Sun to detect polarization from solar flares. The Minimum Detectable Polarization of a 1 mCrab source reaches 14 % in the 2-10 keV band in 10(5) s for pointed observations, and 0.6 % for an X10 class solar flare in the 15-35 keV energy band. The imaging capability is 24 arcsec Half Energy Width (HEW) in a Field of View of 14.7 arcmin x 14.7 arcmin. The spectral resolution is 20 % at 6 keV and the time resolution is 8 mu s. The imaging capabilities of the JET-X optics and of the GPD have been demonstrated by a recent calibration campaign at PANTER X-ray test facility of the Max-Planck-Institut fur extraterrestrische Physik (MPE, Germany). XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil). The data policy is organized with a Core Program that comprises three months of Science Verification Phase and 25 % of net observing time in the following 2 years. A competitive Guest Observer program covers the remaining 75 % of the net observing time.

  • 805.
    Soler, J. D.
    et al.
    Max Planck Inst Astron, Konigstuhl 17, D-69117 Heidelberg, Germany..
    Bracco, Andrea
    KTH. Univ Paris Diderot, CNRS, Lab AIM,Paris Saclay, CEA,IRFU,SAp, F-91191 Gif Sur Yvette, France..
    Pon, A.
    Univ Western Ontario, Dept Phys & Astron, 1151 Richmond St, London, ON N6A 3K7, Canada..
    The magnetic environment of the Orion-Eridanus superbubble as revealed by Planck2018Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 609, artikkel-id L3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using the 353-GHz polarization observations by the Planck satellite we characterize the magnetic field in the Orion-Eridanus super-bubble, a nearby expanding structure that spans more than 1600 square degrees in the sky. We identify a region of both low dispersion of polarization orientations and high polarization fraction associated with the outer wall of the superbubble identified in the most recent models of the large-scale shape of the region. We use the Davis-Chandrasekhar-Fermi method to derive plane-of-the-sky magnetic field strengths of tens of mu G toward the southern edge of the bubble. The comparison of these values with existing Zeeman splitting observations of HI in emission suggests that the large-scale magnetic field in the region was primarily shaped by the expanding superbubble.

  • 806. Solomon, Adam R.
    et al.
    Akrami, Yashar
    Koivisto, Tomi S.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Linear growth of structure in massive bigravity2014Inngår i: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2014, nr 10, s. 066-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ghost-free theory of massive gravity with two dynamical metrics has been shown to produce viable cosmological expansion, where the late-time acceleration of the Universe is due to the finite range of the gravitational interaction rather than a nonzero cosmological constant. Here the cosmological perturbations are studied in this theory. The full perturbation equations are presented in a general gauge and analyzed, focusing on subhorizon scales in the quasistatic limit during the matter-dominated era. An evolution equation for the matter inhomogeneities and the parameters quantifying the deviations from general relativistic structure formation are expressed in terms of five functions whose forms are determined directly by the coupling parameters in the theory. The evolution equation has a similar structure to Horndeski-type scalar-tensor theories, exhibiting a modified growth rate and scale-dependence at intermediate wavenumbers. Predictions of the theory are confronted with observational data on both background expansion and large-scale structure, although care must be taken to ensure a model is stable. It is found that while the stable models tit the data well, they feature deviations from the standard cosmology that could be detected or ruled out by near-future experiments.

  • 807.
    Soucek, J.
    et al.
    Acad Sci Czech Republic, Inst Atmospher Phys, Prague, Czech Republic..
    Åhlén, Lennart
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Bale, S.
    UCB, Space Sci Lab, Berkeley, CA USA..
    Bonnell, J.
    UCB, Space Sci Lab, Berkeley, CA USA..
    Boudin, N.
    ESA ESTEC, Noordwijk, Netherlands..
    Brienza, D.
    IAPS, Rome, Italy..
    Carr, C.
    Imperial Coll, London, England..
    Cipriani, F.
    ESA ESTEC, Noordwijk, Netherlands..
    Escoubet, C. P.
    ESA ESTEC, Noordwijk, Netherlands..
    Fazakerley, A.
    UCL, Mullard Space Sci Lab, Dorking, Surrey, England..
    Gehler, M.
    ESA ESTEC, Noordwijk, Netherlands..
    Genot, V.
    IRAP, Toulouse, France..
    Hilgers, A.
    ESA ESTEC, Noordwijk, Netherlands..
    Hanock, B.
    UCL, Mullard Space Sci Lab, Dorking, Surrey, England..
    Jannet, G.
    LPC2E, Orleans, France..
    Junge, A.
    ESA ESTEC, Noordwijk, Netherlands..
    Khotyaintsev, Yuri
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    De Keyser, J.
    BIRA IASB, Brussels, Belgium..
    Kucharek, H.
    Univ New Hampshire, Durham, NH 03824 USA..
    Lan, R.
    Acad Sci Czech Republic, Inst Atmospher Phys, Prague, Czech Republic..
    Lavraud, B.
    IRAP, Toulouse, France..
    Leblanc, F.
    Plasma Phys Lab, Paris, France..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Mansour, M.
    Plasma Phys Lab, Paris, France..
    Marcucci, M. F.
    IAPS, Rome, Italy..
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Nemecek, Z.
    Charles Univ Prague, Prague, Czech Republic..
    Owen, C.
    UCL, Mullard Space Sci Lab, Dorking, Surrey, England..
    Phal, Y.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Retino, A.
    Plasma Phys Lab, Paris, France..
    Rodgers, D.
    ESA ESTEC, Noordwijk, Netherlands..
    Safrankova, J.
    Charles Univ Prague, Prague, Czech Republic..
    Sahraoui, F.
    Plasma Phys Lab, Paris, France..
    Vainio, R.
    Univ Turku, Turku, Finland..
    Wimmer-Schweingruber, R.
    Univ Kiel, Kiel, Germany..
    Steinhagen, J.
    Univ Kiel, Kiel, Germany..
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Wielders, A.
    ESA ESTEC, Noordwijk, Netherlands..
    Zaslavsky, A.
    Observ Paris, LESIA, Ifeudon, France..
    EMC Aspects Of Turbulence Heating Observer (THOR) Spacecraft2016Inngår i: Proceedings Of 2016 Esa Workshop On Aerospace Emc (Aerospace Emc), Institute of Electrical and Electronics Engineers (IEEE), 2016, artikkel-id 7504544Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Turbulence Heating ObserveR (THOR) is a spacecraft mission dedicated to the study of plasma turbulence in near-Earth space. The mission is currently under study for implementation as a part of ESA Cosmic Vision program. THOR will involve a single spinning spacecraft equipped with state of the art instruments capable of sensitive measurements of electromagnetic fields and plasma particles. The sensitive electric and magnetic field measurements require that the spacecraft-generated emissions are restricted and strictly controlled; therefore a comprehensive EMC program has been put in place already during the study phase. The THOR study team and a dedicated EMC working group are formulating the mission EMC requirements already in the earliest phase of the project to avoid later delays and cost increases related to EMC. This article introduces the THOR mission and reviews the current state of its EMC requirements.

  • 808. Sparvoli, R
    et al.
    Carlson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Lund, Jens
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Lundquist, Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Orsi, Silvio
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Stochaj, S. J.
    al., et
    Space qualification tests of the PAMELA instrument2006Inngår i: ASTROPHYSICS / [ed] Battiston, R; Shea, MA; Rakowski, C; Chatterjee, S, 2006, Vol. 37, nr 10, s. 1841-1847Konferansepaper (Fagfellevurdert)
    Abstract [en]

    PAMELA is a satellite-borne experiment which will measure the antiparticle component of cosmic rays over an extended energy range and with unprecedented accuracy. The apparatus consists of a permanent magnetic spectrometer equipped with a double-sided silicon microstrip tracking system and surrounded by a scintillator anticoincidence system. A silicon-tungsten imaging calorimeter, complemented by a scintillator shower tail catcher, and a transition radiation detector perform the particle identification task. Fast scintillators are used for Time-of-Flight measurements and to provide the primary trigger. A neutron detector is finally provided to extend the range of particle measurements to the TeV region. PAMELA will fly on-board of the Resurs-DKI satellite, which will be put into a semi-polar orbit in 2005 by a Soyuz rocket. We give a brief review of the scientific issues of the mission and report about the status of the experiment few months before the launch.

  • 809.
    Sreehari, H.
    et al.
    URSC, Space Astron Grp, ISITE Campus,Outer Ring Rd, Bangalore 560037, Karnataka, India.;Indian Inst Sci, Bangalore 560012, Karnataka, India..
    Iyer, Nirmal
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Radhika, D.
    Dayananda Sagar Univ, Dept Phys, Bangalore 560068, Karnataka, India..
    Nandi, Anuj
    URSC, Space Astron Grp, ISITE Campus,Outer Ring Rd, Bangalore 560037, Karnataka, India..
    Mandal, Samir
    Indian Inst Space Sci & Technol, Trivandrum 695547, Kerala, India..
    Constraining the mass of the black hole GX 339-4 using spectro-temporal analysis of multiple outbursts2019Inngår i: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 63, nr 3, s. 1374-1386Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We carried out spectro-temporal analysis of the archived data from multiple outbursts spanning over the last two decades from the black hole X-ray binary GX 339-4. In this paper, the mass of the compact object in the X-ray binary system GX 339-4 is constrained based on three indirect methods. The first method uses broadband spectral modelling with a two component flow structure of the accretion around the black hole. The broadband data are obtained from RXTE (Rossi X-ray Timing Explorer) in the range 3.0 to 150.0 keV and from Swift and NuSTAR (Nuclear Spectroscopic Telescope Array) simultaneously in the range 0.5 to 79.0 keV. In the second method, we model the time evolution of Quasi-periodic Oscillation (QPO) frequencies, considering it to be the result of an oscillating shock that radially propagates towards or away from the compact object. The third method is based on scaling a mass dependent parameter from an empirical model of the photon index (Gamma) - QPO (v) correlation. We compare the results at 90 percent confidence from the three methods and summarize the mass estimate of the central object to be in the range 8.28-11.89M(circle dot). 

  • 810. Sreehari, H.
    et al.
    Nandi, Anuj
    Radhika, D.
    Iyer, Nirmal
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Mandal, Samir
    Observational aspects of outbursting black hole sources: Evolution of spectro-temporal features and X-ray variability2018Inngår i: Journal of astrophysics and astronomy, ISSN 0250-6335, E-ISSN 0973-7758, Vol. 39, nr 1, artikkel-id 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on our attempt to understand the outbursting profile of Galactic Black Hole sources, keeping in mind the evolution of temporal and spectral features during the outburst. We present results of evolution of quasi-periodic oscillations, spectral states and possible connection with jet ejections during the outburst phase. Further, we attempt to connect the observedX-ray variabilities (i.e., 'class'/'structured' variabilities, similar to GRS 1915+105) with spectral states of black hole sources. Towards these studies, we consider three black hole sources that have undergone single (XTE J1859+226), a few (IGR J17091-3624) and many (GX 339-4) outbursts since the start of RXTE era. Finally, we model the broadband energy spectra (3-150 keV) of different spectral states using RXTE and NuSTAR observations. Results are discussed in the context of two-component advective flow model, while constraining the mass of the three black hole sources.

  • 811.
    Sreehari, H.
    et al.
    UR Rao Satellite Ctr, Space Astron Grp, ISITE Campus,Outer Ring Rd, Bangalore 560037, Karnataka, India.;Indian Inst Sci, Dept Phys, Bangalore 560012, Karnataka, India..
    Ravishankar, B. T.
    UR Rao Satellite Ctr, Space Astron Grp, ISITE Campus,Outer Ring Rd, Bangalore 560037, Karnataka, India.;Indian Inst Space Sci & Technol, Dept Earth & Space Sci, Thiruvananthapuram 695547, Kerala, India..
    Iyer, Nirmal
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Agrawal, V. K.
    UR Rao Satellite Ctr, Space Astron Grp, ISITE Campus,Outer Ring Rd, Bangalore 560037, Karnataka, India..
    Katoch, Tilak B.
    Tata Inst Fundamental Res, Dept Astron & Astrophys, Homi Bhabha Rd, Mumbai 400005, Maharashtra, India..
    Mandal, Samir
    Indian Inst Space Sci & Technol, Dept Earth & Space Sci, Thiruvananthapuram 695547, Kerala, India..
    Nandi, Anuj
    UR Rao Satellite Ctr, Space Astron Grp, ISITE Campus,Outer Ring Rd, Bangalore 560037, Karnataka, India..
    AstroSat view of MAXI J1535-571: broad-band spectro-temporal features2019Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 487, nr 1, s. 928-941Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the results of Target of Opportunity (ToO) observations made with AstroSat of the newly discovered black hole binary MAXI J1535-571. We detect prominent C-type quasi-periodic oscillations (QPOs) of frequencies varying from 1.85 to 2.88 Hz, along with distinct harmonics in all the AstroSat observations. We note that while the fundamental QPO is seen in the 3-50 keV energy band, the harmonic is not significant above similar to 35 keV. The AstroSat observations were made in the hard intermediate state, as seen from state transitions observed by MAXI and Swift. We attempt spectral modelling of the broad-band data (0.7-80 keV) provided by AstroSat using phenomenological and physical models. The spectral modelling using nthComp gives a photon index in the range 2.18-2.37 and electron temperature ranging from 21 to 63 keV. The seed photon temperature is within 0.19 to 0.29 keV. The high flux in 0.3-80 keV band corresponds to a luminosity varying from 0.7 to 1.07 L-Edd assuming the source to be at a distance of 8 kpc and hosting a black hole with a mass of 6 M-circle dot. The physical model based on the two-component accretion flow gives disc accretion rates as high as similar to 1 (m) over dot(Edd) and halo rate similar to 0.2 (m) over dot(Edd), respectively. The near-Eddington accretion rate seems to be the main reason for the unprecedented high flux observed from this source. The two-component spectral fitting of AstroSat data also provides an estimate of a black hole mass between 5.14 and 7.83 M-circle dot.

  • 812. Sridhar, S.
    et al.
    Singh, Nishant K.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Raman Res Inst, Karnataka, India.
    Large-scale dynamo action due to alpha fluctuations in a linear shear flow2014Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 445, nr 4, s. 3770-3787Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a model of large-scale dynamo action in a shear flow that has stochastic, zero-mean fluctuations of the a parameter. This is based on a minimal extension of the Kraichnan Moffatt model, to include a background linear shear and Galilean-invariant alpha-statistics. Using the firstorder smoothing approximation we derive a linear integro-differential equation for the largescale magnetic field, which is non-perturbative in the shearing rate S, and the alpha-correlation time r. The white-noise case, tau(alpha) = 0, is solved exactly, and it is concluded that the necessary condition for dynamo action is identical to the Kraichnan Moffatt model without shear; this is because white-noise does not allow for memory effects, whereas shear needs time to act. To explore memory effects we reduce the integro-differential equation to a partial differential equation, valid for slowly varying fields when is small but non-zero. Seeking exponential modal solutions, we solve the modal dispersion relation and obtain an explicit expression for the growth rate as a function of the six independent parameters of the problem. A non-zero r, gives rise to new physical scales, and dynamo action is completely different from the white-noise case; e.g. even weak a fluctuations can give rise to a dynamo. We argue that, at any wavenumber, both Moffatt drift and Shear always contribute to increasing the growth rate. Two examples are presented: (a) a Moffatt drift dynamo in the absence of shear and (b) a Shear dynamo in the absence of Moffatt drift.

  • 813.
    Stawarz, J. E.
    et al.
    Imperial Coll London, Dept Phys, London, England..
    Eastwood, J. P.
    Imperial Coll London, Dept Phys, London, England..
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Gingell, I. L.
    Imperial Coll London, Dept Phys, London, England..
    Shay, M. A.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Ergun, R. E.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA.;Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Le Contel, O.
    Univ Paris Sud, Lab Phys Plasmas, CNRS, Ecole Polytech,Sorbonne Univ,Observ Paris, Paris, France..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Argall, M. R.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Fischer, D.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Franci, L.
    Queen Mary Univ London, Sch Phys & Astron, London, England..
    Properties of the Turbulence Associated with Electron-only Magnetic Reconnection in Earth's Magnetosheath2019Inngår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 877, nr 2, artikkel-id L37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Turbulent plasmas generate intense current structures, which have long been suggested as magnetic reconnection sites. Recent Magnetospheric Multiscale observations in Earth's magnetosheath revealed a novel form of reconnection where the dynamics only couple to electrons, without ion involvement. It was suggested that such dynamics were driven by magnetosheath turbulence. In this study, the fluctuations are examined to determine the properties of the turbulence and if a signature of reconnection is present in the turbulence statistics. The study reveals statistical properties consistent with plasma turbulence with a correlation length of similar to 10 ion inertial lengths. When reconnection is more prevalent, a steepening of the magnetic spectrum occurs at the length scale of the reconnecting current sheets. The statistics of intense currents suggest the prevalence of electron-scale current sheets favorable for electron reconnection. The results support the hypothesis that electron reconnection is driven by turbulence and highlight diagnostics that may provide insight into reconnection in other turbulent plasmas.

  • 814. Stozhkov, Y. I.
    et al.
    Basili, A.
    Bencardino, R.
    Casolino, M.
    de Pascale, M. P.
    Furano, G.
    Menicucci, A.
    Minori, M.
    Morselli, A.
    Picozza, P.
    Sparvoli, R.
    Wischnewski, R.
    Bakaldin, A.
    Galper, A. M.
    Koldashov, S. V.
    Korotkov, M. G.
    Mikhailov, V. V.
    Voronov, S. A.
    Yurkin, Y. T.
    Adriani, O.
    Bonechi, L.
    Bongi, M.
    Papini, P.
    Ricciarini, S. B.
    Spillantini, P.
    Straulino, S.
    Taccetti, F.
    Vannuccini, E.
    Castellini, G.
    Boezio, M.
    Bonvicini, M.
    Mocchiutti, E.
    Schiavon, P.
    Vacchi, A.
    Zampa, G.
    Zampa, N.
    Carlson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund, Jens
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lundquist, Johan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Orsi, Silvio
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Barbarino, G. C.
    Campana, D.
    Osteria, G.
    Rossi, G.
    Russo, S.
    Boscherini, M.
    Mennh, W.
    Simonh, M.
    Bongiorno, L.
    Ricci, M.
    Ambriola, M.
    Bellotti, R.
    Cafagna, F.
    Circella, M.
    de Marzo, C.
    Giglietto, N.
    Mirizzi, N.
    Romita, M.
    Spinelli, P.
    Bogomolov, E.
    Krutkov, S.
    Vasiljev, G.
    Bazilevskaya, G. A.
    Kvashnin, A. N.
    Logachev, V. I.
    Makhmutov, V. S.
    Maksumov, O. S.
    Mitchell, J. W.
    Streitmatter, R. E.
    Stochaj, S. J.
    About Separation of Hadron and Electromagnetic Cascades in the Pamela Calorimeter2005Inngår i: International Journal of Modern Physics A, ISSN 0217-751X, E-ISSN 1793-656X, Vol. 20, nr 29, s. 6745-6748Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Results of calibration of the PAMELA instrument at the CERN facilities are discussed. In September, 2003, the calibration of the Neutron Detector together with the Calorimeter was performed with the CERN beams of electrons and protons with energies of 20-180 GeV. The implementation of the Neutron Detector increases a rejection factor of hadrons from electrons about ten times. The results of calibration are in agreement with calculations.

  • 815. Straube, Ulrich
    et al.
    Berger, Thomas
    Reitz, Guenther
    Facius, Rainer
    Fuglesang, Christer
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Reiter, Thomas
    Damann, Volker
    Tognini, Michel
    Operational radiation protection for astronauts and cosmonauts and correlated activities of ESA Medical Operations2010Inngår i: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030, Vol. 66, nr 7-8, s. 963-973Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Since the early times of human spaceflight radiation has been, besides the influence of microgravity on the human body, recognized as a main health concern to astronauts and cosmonauts. The radiation environment that the crew experiences during spaceflight differs significantly to that found on earth due to particles of greater potential for biological damage. Highly energetic charged particles, such as protons, helium nuclei ("alpha particles") and heavier ions up to iron, originating from several sources, as well as protons and electrons trapped in the Earth's radiation belts, are the main contributors. The exposure that the crew receives during a spaceflight significantly exceeds exposures routinely received by terrestrial radiation workers. The European Space Agency's (ESA) Astronaut Center (EAC) in Cologne, Germany, is home of the European Astronaut Corps. Part of the EAC is the Crew Medical Support Office (CMSO or HSF-AM) responsible for ensuring the health and well-being of the European Astronauts. A sequence of activities is conducted to protect astronauts and cosmonauts health, including those aiming to mitigate adverse effects of space radiation. All health related activities are part of a multinational Medical Operations (MedOps) concept, which is executed by the different Space Agencies participating in the human spaceflight program of the International Space Station (ISS). This article will give an introduction to the current measures used for radiation monitoring and protection of astronauts and cosmonauts. The operational guidelines that shall ensure proper implementation and execution of those radiation protection measures will be addressed. Operational hardware for passive and active radiation monitoring and for personal dosimetry, as well as the operational procedures that are applied, are described.

  • 816. Subramanian, Kandaswamy
    et al.
    Brandenburg, Axel
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Traces of large-scale dynamo action in the kinematic stage2014Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 445, nr 3, s. 2930-2940Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using direct numerical simulations (DNS), we verify that in the kinematic regime, a turbulent helical dynamo grows in such a way that the magnetic energy spectrum remains to high-precision shape-invariant, i.e. at each wavenumber k the spectrum grows with the same growth rate. Signatures of large-scale dynamo action can be identified through the excess of magnetic energy at small k, of one of the two oppositely polarized constituents. Also a suitably defined planar average of the magnetic field can be chosen such that its rms value isolates the strength of the mean field. However, these different means of analysis suggest that the strength of the large-scale field diminishes with increasing magnetic Reynolds number Re-M like Re(M)(-1/2)for intermediate values and like Re-M(-3/4) for larger ones. Both an analysis from the Kazantsev model including helicity and the DNS show that this arises due to the magnetic energy spectrum still peaking at resistive scales, even when helicity is present. As expected, the amplitude of the large-scale field increases with increasing fractional helicity, enabling us to determine the onset of large-scale dynamo action and distinguishing it from that of the small-scale dynamo. Our DNS show that, contrary to earlier results for smaller scale separation (only 1.5 instead of now 4), the small-scale dynamo can still be excited at magnetic Prandtl numbers of 0.1 and only moderate values of the magnetic Reynolds numbers (similar to 160).

  • 817.
    Sukhachov, Pavlo O.
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Rakov, Mykhailo V.
    Syst Univers Braunschweig, Institut Mathemat Phys, Mendelssohnstrasse 3, DE-38106 Braunschweig, Germany.;Kyiv Natl Taras Shevchenko Univ, Fac Phys, 64/13 Volodymyrska st., Kiev UA-01601, Kiev, Ukraine..
    Teslyk, Olena M.
    Kyiv Natl Taras Shevchenko Univ, Fac Phys, 64/13 Volodymyrska st., Kiev UA-01601, Kiev, Ukraine..
    Gorbar, Eduard V.
    Kyiv Natl Taras Shevchenko Univ, Fac Phys, 64/13 Volodymyrska st., Kiev UA-01601, Kiev, Ukraine.;Bogolyubov Inst Theoret Phys, Kiev UA-03680, Kiev, Ukraine..
    Fermi Arcs and DC Transport in Nanowires of Dirac and Weyl Semimetals2020Inngår i: Annalen der Physik, ISSN 0003-3804, E-ISSN 1521-3889, Vol. 532, nr 2, artikkel-id 1900449Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The transport properties and electron states in cylinder nanowires of Dirac and Weyl semimetals are studied paying special attention to the structure and properties of the surface Fermi arcs. The latter make the electric charge and current density distributions in nanowires strongly nonuniform as the majority of the charge density is accumulated at the surface. It is found that a Weyl semimetal wire also supports a magnetization current localized mainly at the surface because of the Fermi arcs contribution. By using the Kubo linear response approach, the direct current (DC) conductivity is calculated and it is found that its spatial profile is nontrivial. By explicitly separating the contributions of the surface and bulk states, it is shown that when the electric chemical potential and/or the radius of the wire is small, the electron transport is determined primarily by the Fermi arcs and the electrical conductivity is much higher at the surface than in the bulk. Due to the rise of the surface-bulk transition rate, the relative contribution of the surface states to the total conductivity gradually diminishes as the chemical potential increases. In addition, the DC conductivity at the surface demonstrates noticeable peaks when the Fermi level crosses energies of the surface states.

  • 818. Suleimanov, V. F.
    et al.
    Kajava, J. J. E.
    Molkov, S. V.
    Nättilä, J.
    Lutovinov, A. A.
    Werner, K.
    Poutanen, Juri
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Basic parameters of the helium-accreting X-ray bursting neutron star in 4U 1820-302017Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 472, nr 4, s. 3905-3913, artikkel-id stx2234Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ultracompact low-mass X-ray binary 4U 1820-30 situated in the globular cluster NGC 6624 has an orbital period of only ≈11.4 min, which likely implies a white dwarf companion. The observed X-ray bursts demonstrate a photospheric radius expansion phase and therefore are believed to reach the Eddington luminosity, allowing us to estimate the mass and the radius of the neutron star (NS) in this binary. Here, we re-analyse all Rossi X-ray Timing Explorer observations of the system and confirm that almost all the bursts took place during the hard persistent state of the system. This allows us to use the recently developed direct cooling tail method to estimate the NS mass and radius. However, because of the very short, about a second, duration of the cooling tail phases that can be described by the theoretical atmosphere models, the obtained constraints on the NS radius are not very strict. Assuming a pure helium NS atmosphere, we found that the NS radius is in the range 10-12 km, if the NS mass is below 1.7 MO˙, and in a wider range of 8-12 km for a higher 1.7-2.0 Mo˙ NS mass. The method also constrains the distance to the system to be 6.5 ± 0.5 kpc, which is consistent with the distance to the cluster. For the solar composition atmosphere, the NS parameters are in strong contradiction with the generally accepted range of possible NS masses and radii.

  • 819. Suleimanov, V. F.
    et al.
    Klochkov, D.
    Poutanen, Juri
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. University of Turku, Finland.
    Werner, K.
    Probing the possibility of hotspots on the central neutron star in HESSJ1731-3472017Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 600, artikkel-id A43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The X-ray spectra of the neutron stars located in the centers of supernova remnants Cas A and HESS J1731-347 are well fit with carbon atmosphere models. These fits yield plausible neutron star sizes for the known or estimated distances to these supernova remnants. The evidence in favor of the presence of a pure carbon envelope at the neutron star surface is rather indirect and is based on the assumption that the emission is generated uniformly by the entire stellar surface. Although this assumption is supported by the absence of pulsations, the observational upper limit on the pulsed fraction is not very stringent. In an attempt to quantify this evidence, we investigate the possibility that the observed spectrum of the neutron star in HESS J1731-347 is a combination of the spectra produced in a hydrogen atmosphere of the hotspots and of the cooler remaining part of the neutron star surface. The lack of pulsations in this case has to be explained either by a sufficiently small angle between the neutron star spin axis and the line of sight, or by a sufficiently small angular distance between the hotspots and the neutron star rotation poles. As the observed flux from a non-uniformly emitting neutron star depends on the angular distribution of the radiation emerging from the atmosphere, we have computed two new grids of pure carbon and pure hydrogen atmosphere model spectra accounting for Compton scattering. Using new hydrogen models, we have evaluated the probability of a geometry that leads to a pulsed fraction below the observed upper limit to be about 8.2%. Such a geometry thus seems to be rather improbable but cannot be excluded at this stage.

  • 820.
    Suleimanov, V. F.
    et al.
    Univ Tubingen, Kepler Ctr Astro & Particle Phys, Inst Astron & Astrophys, Sand 1, D-72076 Tubingen, Germany.;Kazan Volga Reg Fed Univ, Astron Dept, Kremlyovskaya Str 18, Kazan 420008, Russia.;Russian Acad Sci, Space Res Inst, Profsoyuznaya Str 84-32, Moscow 117997, Russia..
    Poutanen, Juri
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Russian Acad Sci, Space Res Inst, Profsoyuznaya Str 84-32, Moscow 117997, Russia.;Univ Turku, Dept Phys & Astron, Tuorla Observ, Turku 20014, Finland.;Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden..
    Werner, K.
    Univ Tubingen, Kepler Ctr Astro & Particle Phys, Inst Astron & Astrophys, Sand 1, D-72076 Tubingen, Germany..
    Accretion heated atmospheres of X-ray bursting neutron stars2018Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 619, artikkel-id A114Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Some thermonuclear (type I) X-ray bursts at the neutron star surfaces in low-mass X-ray binaries take place during hard persistent states of the systems. Spectral evolution of these bursts is well described by the atmosphere model of a passively cooling neutron star when the burst luminosity is high enough. The observed spectral evolution deviates from the model predictions when the burst luminosity drops below a critical value of 20-70% of the maximum luminosity. The amplitude of the deviations and the critical luminosity correlate with the persistent luminosity, which leads us to suggest that these deviations are induced by the additional heating of the accreted particles. We present a method for computation of the neutron star atmosphere models heated by accreted particles assuming that their energy is released via Coulomb interactions with electrons. We computed the temperature structures and the emergent spectra of the atmospheres of various chemical compositions and investigate the dependence of the results on the velocity of accreted particles, their temperature and the penetration angle. We show that the heated atmosphere develops two different regions. The upper one is the hot (20-100 keV) corona-like surface layer cooled by Compton scattering, and the deeper, almost isothermal optically thick region with a temperature of a few keV. The emergent spectra correspondingly have two components: a blackbody with the temperature close to that of the isothermal region and a hard Comptonized component (a power law with an exponential decay). Their relative contribution depends on the ratio of the energy dissipation rate of the accreted particles to the intrinsic flux from the neutron star surface. These spectra deviate strongly from those of undisturbed, passively cooling neutron star atmospheres, with the main differences being the presence of a high-energy tail and a strong excess in the low-energy part of the spectrum. They also lack the iron absorption edge, which is visible in the spectra of undisturbed low-luminosity atmospheres with solar chemical composition. Using the computed spectra, we obtained the dependences of the dilution and color-correction factors as functions of relative luminosities for pure helium and solar abundance atmospheres. We show that the helium model atmosphere heated by accretion corresponding to 5% of the Eddington luminosity describes well the late stages of the X-ray bursts in 4U 1820-30.

  • 821. Suleimanov, Valery F.
    et al.
    Poutanen, Juri
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Univ Turku, Finland.
    Nattila, Joonas
    Kajava, Jari J. E.
    Revnivtsev, Mikhail G.
    Werner, Klaus
    The direct cooling tail method for X-ray burst analysis to constrain neutron star masses and radii2017Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 466, nr 1, s. 906-913Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Determining neutron star (NS) radii and masses can help to understand the properties of matter at supra-nuclear densities. Thermal emission during thermonuclear X-ray bursts from NSs in low-mass X-ray binaries provides a unique opportunity to study NS parameters, because of the high fluxes, large luminosity variations and the related changes in the spectral properties. The standard cooling tail method uses hot NS atmosphere models to convert the observed spectral evolution during cooling stages of X-ray bursts to the Eddington flux F-Edd and the stellar angular size Omega. These are then translated to the constraints on the NS massMand radius R. Here we present the improved, direct cooling tail method that generalizes the standard approach. First, we adjust the cooling tail method to account for the bolometric correction to the flux. Then, we fit the observed dependence of the blackbody normalization on flux with a theoretical model directly on theM-R plane by interpolating theoretical dependences to a given gravity, hence ensuring only weakly informative priors for M and R instead of FEdd and Omega. The direct cooling method is demonstrated using a photospheric radius expansion burst from SAX J1810.8-2609, which has happened when the system was in the hard state. Comparing to the standard cooling tail method, the confidence regions are shifted by 1 sigma towards larger radii, giving R = 11.5-13.0 km at M = 1.3-1.8M(circle dot) for this NS.

  • 822. Sullivan, J. M.
    et al.
    Ivchenko, Nickolay V.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Lockwood, M.
    Grydeland, T.
    Blixt, E. M.
    Lanchester, B. S.
    Phase calibration of the EISCAT Svalbard Radar interferometer using optical satellite signatures2006Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 24, nr 9, s. 2419-2427Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The link between natural ion-line enhancements in radar spectra and auroral activity has been the subject of recent studies but conclusions have been limited by the spatial and temporal resolution previously available. The next challenge is to use shorter sub-second integration times in combination with interferometric programmes to resolve spatial structure within the main radar beam, and so relate enhanced filaments to individual auroral rays. This paper presents initial studies of a technique, using optical and spectral satellite signatures, to calibrate the received phase of a signal with the position of the scattering source along the interferometric baseline of the EISCAT Svalbard Radar. It is shown that a consistent relationship can be found only if the satellite passage through the phase fringes is adjusted from the passage predicted by optical tracking. This required adjustment is interpreted as being due to the vector between the theoretical focusing points of the two antennae, i.e. the true radar baseline, differing from the baseline obtained by survey between the antenna foot points. A method to obtain a measurement of the true interferometric baseline using multiple satellite passes is outlined.

  • 823.
    Sundberg, Torbjörn
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Boardsen, S. A.
    Slavin, J. A.
    Blomberg, Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Korth, H.
    The Kelvin-Helmholtz instability at Mercury: An assessment2010Inngår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 58, nr 11, s. 1434-1441Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Kelvin-Helmholtz instability is believed to be an important means for the transfer of energy, plasma, and momentum from the solar wind into planetary magnetospheres, with in situ measurements reported from Earth, Saturn, and Venus. During the first MESSENGER flyby of Mercury, three periodic rotations were observed in the magnetic field data possibly related to a Kelvin-Helmholtz wave on the dusk side magnetopause. We present an analysis of the event, along with comparisons to previous Kelvin-Helmholtz observations and an investigation of what influence finite ion gyro radius effects, believed to be of importance in the Hermean magnetosphere, may have on the instability. The wave signature does not correspond to that of typical Kelvin-Helmholtz events, and the magnetopause direction does not show any signs of major deviation from the unperturbed case. There is thus no indication of any high amplitude surface waves. On the other hand, the wave period corresponds to that expected for a Kelvin-Helmholtz wave, and as the dusk side is shown to be more stable than the dawn side, we judge the observed waves not to be fully developed Kelvin-Helmholtz waves, but they may be an initial perturbation that could cause Kelvin-Helmholtz waves further down the tail. (C) 2010 Elsevier Ltd. All rights reserved.

  • 824.
    Sundell, Peter
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Mortsell, Edvard
    Stockholm Univ, Oskar Klein Ctr Cosmoparticle Phys, AlbaNova Univ Ctr, SE-10691 Stockholm, Sweden.;Stockholm Univ, Dept Phys, AlbaNova Univ Ctr, SE-10691 Stockholm, Sweden..
    Vilja, Iiro
    Univ Turku, Dept Phys & Astron, Turku Ctr Quantum Phys, FIN-20014 Turku, Finland..
    Can a void mimic the Lambda in Lambda CDM?2015Inngår i: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, nr 8, artikkel-id 037Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate Lematre-Tolman-Bondi (LTB) models, whose early time evolution and bang time are homogeneous and the distance-redshift relation and local Hubble parameter are inherited from the Lambda CDM model. We show that the obtained LTB models and the Lambda CDM model predict different relative local expansion rates and that the Hubble functions of the models diverge increasingly with redshift. The LTB models show tension between low redshift baryon acoustic oscillation and supernova observations and including Lyman-alpha forest or cosmic microwave background observations only accentuates the better fit of the Lambda CDM model compared to the LTB model. The result indicates that additional degrees of freedom are needed to explain the observations, for example by renouncing spherical symmetry, homogeneous bang time, negligible effects of pressure, or the early time homogeneity assumption.

  • 825. Takahashi, H.
    et al.
    Matsuoka, M.
    Umeki, Y.
    Yoshida, H.
    Tanaka, T.
    Mizuno, T.
    Fukazawa, Y.
    Kamae, T.
    Madejski, G.
    Tajima, H.
    Kiss, Mózsi Bank
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Klamra, Wlodzimierz
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Bettolo, Cecilia Marini
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Rydström, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Kurita, K.
    Kanai, Y.
    Arimoto, M.
    Ueno, M.
    Kataoka, J.
    Kawai, N.
    Axelsson, Magnus
    Stockholm University.
    Hjalmarsdotter, L.
    Bogaert, G.
    Gunji, S.
    Katsuta, J.
    Takahashi, T.
    Varner, G.
    Yuasa, T.
    The Polarized Gamma-Ray Observer, PoGOLite2010Inngår i: Transactions of the Japanese Society for Artificial Intelligence, Aerospace Technology Japan, Vol. 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Polarized Gamma-ray Observer, PoGOLite, is a balloon experiment with the capability of detecting 10% polarization from a 200 mCrab celestial object in the energy-range 25–80 keV. During a beam test at KEK-PF in 2008, 19 detector units and one anti-coincidence detector were assembled, and a 50 keV X-ray beam with a polarization degree of ∼90% was irradiated at the center unit. Signals from all 20 units were fed into flight-version electronics consisting of six circuit boards (four waveform digitizer boards, one digital I/O board and one router board) and one microprocessor (SpaceCube), which communicate using a SpaceWire interface. One digitizer board, which can associate up to 8 detectors, outputs a trigger signal. The digital I/O board handles the trigger and returns a data acquisition request if there is no veto signal (upper or pulse-shape discriminators) from any detector unit. This data acquisition system worked well, and the modulation factor was successfully measured to be ∼34%. These results confirmed the capabilities of the data-acquisition system for a “pathfinder” flight planned in 2010.

  • 826. Takahashi, H.
    et al.
    Matsuoka, M.
    Umeki, Y.
    Yoshida, H.
    Tanaka, T.
    Mizuno, T.
    Fukazawa, Y.
    Kamae, T.
    Madejski, G.
    Tajima, H.
    Kiss, Mózsi Bank
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Klamra, Wlodzimierz
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Marini Bettolo, Cecilia
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Rydstrom, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Kurita, K.
    Kanai, Y.
    Arimoto, M.
    Ueno, M.
    Kataoka, J.
    Kawai, N.
    Axelsson, M.
    Hjalmarsdotter, L.
    Bogaert, G.
    Gunji, S.
    Takahashi, T.
    Varner, G.
    Yuasa, T.
    Beam test results of the polarized gamma-ray observer, PoGOLite2008Inngår i: 2008 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE (2008 NSS/MIC), VOLS 1-9, 2008, s. 732-736Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Polarized Gamma-ray Observer, PoGOLite, is a balloon experiment with the capability of detecting 10% polarization from a 200 mCrab celestial object in the energy range 25 #x2013;80 keV. During a beam test at KEK-PF in February 2008, 20 detector units were assembled, and a 50 keV X-ray beam with a polarization degree of #x223C;90% was irradiated at the center unit. Signals from all 20 units were fed into flightversion electronics consisting of six circuit boards (four waveform digitizer boards, one digital I/O board and one router board) and one microprocessor (SpaceCube), which communicate using a SpaceWire interface. One digitizer board, which can associate up to 8 PDCs, outputs a trigger signal. The digital I/O board handles the trigger and returns a data acquisition request if there is no veto signal (upper or pulse-shape discriminators) from any detector unit. This data acquisition system worked well, and the modulation factor was successfully measured to be #x223C;34%. These results confirmed the capabilities of both detector and data-acquisition system for a pathfinder flight planned in 2010.

  • 827. Takahashi, H.
    et al.
    Yonetani, M.
    Matsuoka, M.
    Mizuno, T.
    Fukazawa, Y.
    Yanagida, T.
    Fujimoto, Y.
    Yokota, Y.
    Yoshikawa, A.
    Kawaguchi, N.
    Ishizu, S.
    Fukuda, K.
    Suyama, T.
    Watanabe, K.
    Tajima, H.
    Kanai, Y.
    Kawai, N.
    Kataoka, J.
    Katsuta, J.
    Takahashi, T.
    Gunji, S.
    Axelsson, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Jackson, Miranda
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Kiss, Mózsi Bank
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Klamra, Wlodzimierz
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Kole, Merlin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Mallol, Parera Pau
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Rydström, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Olofsson, G.
    Floren, H.
    Kamae, T.
    Madejski, G.
    Varner, G.
    A thermal-neutron detector with a phoswich system of LiCaAlF6 and BGO crystal scintillators onboard PoGOLite2010Inngår i: 2010 IEEE Nuclear Science Symposium, Medical Imaging Conference, NSS/MIC 2010 and 17th International Workshop on Room-Temperature Semiconductor X-ray and Gamma-ray Detectors, RTSD 2010, 2010, s. 32-37Konferansepaper (Fagfellevurdert)
    Abstract [en]

    To measure the flux of atmospheric neutrons and study the neutron contribution to the background of the main detector of the PoGOLite (Polarized Gamma-ray Observer) balloon-borne experiment, a thermal-neutron detector with a phoswich system of LiCaAlF6 (Eu) and BGO crystal scintillators is developed. The performance to separate thermal-neutron events from those of gamma-rays and charged particles is validated with 252Cf on ground. The detector is attached to the PoGOLite instrument and is launched in 2011 from the Esrange facility in the North of Sweden. Although the emission wavelength of the LiCaAlF6 (Ce) is 300 nm and overlaps with the absorption wavelength of the BGO, the phoswich capability of the LiCaAlF6 (Ce) with the BGO is also confirmed with installing a waveform shifter.

  • 828. Tanaka, T.
    et al.
    Arimoto, M.
    Axelsson, Magnus
    Stockholm University.
    Bjornsson, C. -I
    Bogaert, G.
    Carlson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Cooney, M.
    Craig, W.
    Engdegård, Olle
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Fukazawa, Y.
    Gunji, S.
    Hjalmarsdotter, L.
    Kamae, T.
    Kanai, Y.
    Kataoka, J.
    Katsuta, J.
    Kawai, N.
    Kazejev, Jaroslav
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Kiss, Mozsi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Klamra, Wlodzimierz
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Larsson, Stefan
    Madejski, G.
    Bettolo, Cecilia Marini
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Mizuno, T.
    Ng, J.
    Nomachi, M.
    Odaka, H.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ruckman, L.
    Ryde, F.
    Tajima, H.
    Takahashi, H.
    Takahashi, T.
    Thurston, T.
    Ueno, M.
    Varner, G.
    Ylinen, T.
    Yoshida, H.
    Yuasa, T.
    Data acquisition system for the PoGOLite astronomical hard X-ray polarimeter2007Inngår i: 2007 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE RECORD, VOLS 1-11, 2007, Vol. 1, s. 445-449Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The PoGOLite is a new balloon-borne instrument to measure the polarization of hard X-rays / soft gamma-rays in the 25-80 keV energy range for the first time. In order to detect the polarization, PoGOLite measures the azimuthal angle asymmetry of Compton scattering and the subsequent photo- absorption in an array of detectors. This array consists of 217 well-type phoswich detector cells (PDCs) surrounded by a side anti-coincidence shield (SAS) composed of 54 segments of BGO crystals. At balloon altitude, the intensity of backgrounds due to cosmic-ray charged particles, atmospheric gamma-rays and neutrons is extremely high, typically a few hundred Hz per unit. Hence the data acquisition (DAQ) system of PoGOLite is required to handle more than 270 signals simultaneously, and detect weak signals from astrophysical objects (lOOmCrab, 1.5 cs-1 in 25-80 keV ) under such a severe environment. We have developed a new DAQ system consisting of front-end electronics, waveform digitizer, field programmable gate array (FPGA) and a microprocessor. In this system, all output signals of PDC / SAS are fed into individual charge-sensitive amplifier and then digitized to 12 bit accuracy at 24MSa/s by pipelined analog to digital converters. A DAQ board for the PDC records waveforms which will be examined in an off-line analysis to distinguish signals from the background events and measure the energy spectrum and polarization of targets. A board for the SAS records hit pattern to be used for background rejection. It also continuously records a pulse-height analysis (PHA) histogram to monitor incident background flux. These basic functions of the DAQ system were verified in a series of beam tests.

  • 829. Tatischeff, V.
    et al.
    De Angelis, A.
    Tavani, M.
    Grenier, I.
    Oberlack, U.
    Hanlon, L.
    Walter, R.
    Argan, A.
    Von Ballmoos, P.
    Bulgarelli, A.
    Donnarumma, I.
    Hernanz, M.
    Kuvvetli, I.
    Mallamaci, M.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zdziarski, A.
    Aboudan, A.
    Ajello, M.
    Ambrosi, G.
    Bernard, D.
    Bernardini, E.
    Bonvicini, V.
    Brogna, A.
    Branchesi, M.
    Budtz-Jorgensen, C.
    Bykov, A.
    Campana, R.
    Cardillo, M.
    Marisaldi, Mario
    KTH.
    Zoglauer, A.
    et al,
    The e-ASTROGAM gamma-ray space observatory for the multimessenger astronomy of the 2030s2018Inngår i: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2018, artikkel-id 10699Konferansepaper (Fagfellevurdert)
    Abstract [en]

    e-ASTROGAM is a concept for a breakthrough observatory space mission carrying a γ-ray telescope dedicated to the study of the non-thermal Universe in the photon energy range from 0.15 MeV to 3 GeV. The lower energy limit can be pushed down to energies as low as 30 keV for gamma-ray burst detection with the calorimeter. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with remarkable polarimetric capability. Thanks to its performance in the MeV-GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous and current generation instruments, e-ASTROGAM will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will be a major player of the multiwavelength, multimessenger time-domain astronomy of the 2030s, and provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LISA, LIGO, Virgo, KAGRA, the Einstein Telescope and the Cosmic Explorer, IceCube-Gen2 and KM3NeT, SKA, ALMA, JWST, E-ELT, LSST, Athena, and the Cherenkov Telescope Array.

  • 830. Tavani, M.
    et al.
    Giuliani, A.
    Chen, A. W.
    Argan, A.
    Barbiellini, G.
    Bulgarelli, A.
    Caraveo, P.
    Cattaneo, P. W.
    Cocco, V.
    Contessi, T.
    D’Ammando, F.
    Costa, E.
    De Paris, G.
    Del Monte, E.
    Di Cocco, G.
    Donnarumma, I.
    Evangelista, Y.
    Ferrari, A.
    Feroci, M.
    Fuschino, F.
    Galli, M.
    Gianotti, F.
    Labanti, C.
    Lapshov, I.
    Lazzarotto, F.
    Lipari, P.
    Longo, F.
    Marisaldi, M.
    Mastropietro, M.
    Mereghetti, S.
    Morelli, E.
    Moretti, Elena
    University and INFN of Trieste.
    Morselli, A.
    Pacciani, L.
    Pellizzoni, A.
    Perotti, F.
    Piano, G.
    Picozza, P.
    Pilia, M.
    Pucella, G.
    Prest, M.
    Rapisarda, M.
    Rappoldi, A.
    Scalise, E.
    Rubini, A.
    Sabatini, S.
    Striani, E.
    Soffitta, P.
    Trifoglio, M.
    Trois, A.
    Vallazza, E.
    Vercellone, S.
    Vittorini, V.
    Zambra, A.
    Zanello, D.
    Pittori, C.
    Verrecchia, F.
    Santolamazza, P.
    Giommi, P.
    Colafrancesco, S.
    Antonelli, L. A.
    Salotti, L.
    Direct Evidence for Hadronic Cosmic-Ray Acceleration in the Supernova Remnant IC 4432010Inngår i: The Astrophysical Journal. Letters, ISSN 2041-8205, Vol. 710, nr 2, s. L151-L155Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The supernova remnant (SNR) IC 443 is an intermediate-age remnant well known for its radio, optical, X-ray, and gamma-ray energy emissions. In this Letter, we study the gamma-ray emission above 100 MeV from IC 443 as obtained by the AGILE satellite. A distinct pattern of diffuse emission in the energy range 100 MeV-3 GeV is detected across the SNR with its prominent maximum (source "A") localized in the northeastern shell with a flux F = (47 +/- 10) x 10(-8) photons cm(-2) s(-1) above 100 MeV. This location is the site of the strongest shock interaction between the SNR blast wave and the dense circumstellar medium. Source "A" is not coincident with the TeV source located 0.4. away and associated with a dense molecular cloud complex in the SNR central region. From our observations, and from the lack of detectable diffuse TeV emission from its northeastern rim, we demonstrate that electrons cannot be the main emitters of gamma rays in the range 0.1-10 GeV at the site of the strongest SNR shock. The intensity, spectral characteristics, and location of the most prominent gamma-ray emission together with the absence of cospatial detectable TeV emission are consistent only with a hadronic model of cosmic-ray acceleration in the SNR. A high-density molecular cloud (cloud "E") provides a remarkable "target" for nucleonic interactions of accelerated hadrons; our results show enhanced gamma-ray production near the molecular cloud/shocked shell interaction site. IC 443 provides the first unambiguous evidence of cosmic-ray acceleration by SNRs.

  • 831. Tavani, M.
    et al.
    Sabatini, S.
    Pian, E.
    Bulgarelli, A.
    Caraveo, P.
    Viotti, R. F.
    Corcoran, M. F.
    Giuliani, A.
    Pittori, C.
    Verrecchia, F.
    Vercellone, S.
    Mereghetti, S.
    Argan, A.
    Barbiellini, G.
    Boffelli, F.
    Cattaneo, P. W.
    Chen, A. W.
    Cocco, V.
    D’Ammando, F.
    Costa, E.
    DeParis, G.
    Del Monte, E.
    Di Cocco, G.
    Donnarumma, I.
    Evangelista, Y.
    Ferrari, A.
    Feroci, M.
    Fiorini, M.
    Froysland, T.
    Fuschino, F.
    Galli, M.
    Gianotti, F.
    Labanti, C.
    Lapshov, I.
    Lazzarotto, F.
    Lipari, P.
    Longo, F.
    Marisaldi, M.
    Mastropietro, M.
    Morelli, E.
    Moretti, Elena
    University and INFN of Trieste.
    Morselli, A.
    Pacciani, L.
    Pellizzoni, A.
    Perotti, F.
    Piano, G.
    Picozza, P.
    Pilia, M.
    Porrovecchio, G.
    Pucella, G.
    Prest, M.
    Rapisarda, M.
    Rappoldi, A.
    Rubini, A.
    Soffitta, P.
    Trifoglio, M.
    Trois, A.
    Vallazza, E.
    Vittorini, V.
    Zambra, A.
    Zanello, D.
    Santolamazza, P.
    Giommi, P.
    Colafrancesco, S.
    Antonelli, L. A.
    Salotti, L.
    Detection of Gamma-Ray Emission from the Eta-Carinae Region2009Inngår i: ASTROPHYSICAL JOURNAL LETTERS, ISSN 2041-8205, Vol. 698, nr 2, s. L142-L146Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the results of extensive observations by the gamma-ray AGILE satellite of the Galactic region hosting the Carina nebula and the remarkable colliding wind binary Eta Carinae (eta Car) during the period 2007 July-2009 January. We detect a gamma-ray source (1AGL J1043-5931) consistent with the position of eta Car. If 1AGL J1043-5931 is associated with the Car system, our data provide the long sought first detection above 100 MeV of a colliding wind binary. The average gamma-ray flux above 100 MeV and integrated over the preperiastron period 2007 July-2008 October is F(gamma) = (37 +/- 5) x 10(-8) ph cm(-2) s(-1) corresponding to an average gamma-ray luminosity of L(gamma) = 3.4 x 10(34) erg s(-1) for a distance of 2.3 kpc. We also report a two-day gamma-ray flaring episode of 1AGL J1043-5931 on 2008 October 11-13 possibly related to a transient acceleration and radiation episode of the strongly variable shock in the system.

  • 832.
    Tenkanen, Tommi
    et al.
    Johns Hopkins Univ, Dept Phys & Astron, 3400 N Charles St, Baltimore, MD 21218 USA..
    Visinelli, Luca
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Uppsala Univ, Dept Phys & Astron, Lagerhyddsvagen 1, S-75120 Uppsala, Sweden.;Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.;Univ Amsterdam, Gravitat Astroparticle Phys Amsterdam GRAPPA, Inst Theoret Phys Amsterdam, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands.;Univ Amsterdam, Delta Inst Theoret Phys, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands..
    Axion dark matter from Higgs inflation with an intermediate H-*2019Inngår i: JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, nr 8, artikkel-id 033Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to accommodate the QCD axion as the dark matter (DM) in a model in which the Peccei-Quinn (PQ) symmetry is broken before the end of inflation, a relatively low scale of inflation has to be invoked in order to avoid bounds from DM isocurvature fluctuations, H-* less than or similar to O(10(9)) GeV. We construct a simple model in which the Standard Model Higgs field is non-minimally coupled to Palatini gravity and acts as the inflaton, leading to a scale of inflation H-* similar to 10(8) GeV. When the energy scale at which the PQ symmetry breaks is much larger than the scale of inflation, we find that in this scenario the required axion mass for which the axion constitutes all DM is m(0) less than or similar to 0.05 mu eV for a quartic Higgs self-coupling lambda phi= 0.1, which correspond to the PQ breaking scale v(sigma) greater than or similar to 10(14) GeV and tensor-to-scalar ratio r similar to 10(-12). Future experiments sensitive to the relevant QCD axion mass scale can therefore shed light on the physics of the Universe before the end of inflation.

  • 833. Tierney, D
    et al.
    McBreen, S
    Preece, R D
    Fitzpatrick, G
    Foley, S
    Guiriec, S
    Bissaldi, E
    Briggs, M S
    Burgess, James Michael
    University of Alabama in Huntsville, United States.
    Connaughton, V
    Goldstein, A
    Greiner, J
    Gruber, D
    Kouveliotou, C
    McGlynn, S
    Paciesas, W S
    Pelassa, V
    Von Kienlin, A
    Anomalies in low-energy gamma-ray burst spectra with the Fermi Gamma-ray Burst Monitor2013Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 550Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context: A Band function has become the standard spectral function used to describe the prompt emission spectra of gamma-ray bursts (GRBs). However, deviations from this function have previously been observed in GRBs detected by BATSE and in individual GRBs from the Fermi era.

    Aims: We present a systematic and rigorous search for spectral deviations from a Band function at low energies in a sample of the first two years of high fluence, long bursts detected by the Fermi Gamma-ray Burst Monitor (GBM). The sample contains 45 bursts with a fluence greater than 2 × 10-5 erg/cm2 (10-1000 keV).

    Methods: An extrapolated fit method is used to search for low-energy spectral anomalies, whereby a Band function is fit above a variable low-energy threshold and then the best fit function is extrapolated to lower energy data. Deviations are quantified by examining residuals derived from the extrapolated function and the data and their significance is determined via comprehensive simulations which account for the instrument response. This method was employed for both time-integrated burst spectra and time-resolved bins defined by a signal-to-noise ratio of 25σ and 50σ.

    Results: Significant deviations are evident in 3 bursts (GRB 081215A, GRB 090424 and GRB 090902B) in the time-integrated sample (~7%) and 5 bursts (GRB 090323, GRB 090424, GRB 090820, GRB 090902B and GRB 090926A) in the time-resolved sample (~11%).

    Conclusions: The advantage of the systematic, blind search analysis is that it can demonstrate the requirement for an additional spectral component without any prior knowledge of the nature of that extra component. Deviations are found in a large fraction of high fluence GRBs; fainter GRBs may not have sufficient statistics for deviations to be found using this method.

  • 834.
    Tomac, Maximillian
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Rizzi, Arthur
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Jirasek, A.
    Computational Fluid Dynamics Predictions of Control-Surface Effects for F-16XL Aircraft2017Inngår i: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 54, nr 2, s. 395-408Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Computational fluid dynamics methods play an increasingly important role in aircraft design and development. Some examples are conditions that cannot be tested before a flight test. To rely on these methods, it is essential that they are assessed and evaluated with a state-of-the-art wind tunnel test and/or in-flight data. In a previous project, Cranked-Arrow Wing Aerodynamics Project International, it was reported that all computational fluid dynamics methods failed to some degree in the transonic regime where shock-vortex interaction phenomena were present. Detailed analysis of surface pressure distribution showed that computational fluid dynamics was not able replicate the correct flowfield and produce acceptable results. This paper aims to restudy those transonic flight conditions for which computational fluid dynamics underperforms and to try to determine or shed light on the extent to which surface effects contribute to the computational fluid dynamics predictions.

  • 835. Topchiev, N. P.
    et al.
    Galper, A. M.
    Bonvicini, V.
    Adriani, O.
    Aptekar, R. L.
    Arkhangelskaja, I. V.
    Arkhangelskiy, A. I.
    Bergstrom, L.
    Berti, E.
    Bigongiari, G.
    Bobkov, S. G.
    Bogomolov, E. A.
    Boezio, M.
    Bongi, M.
    Bonechi, S.
    Bottai, S.
    Boyarchuk, K. A.
    Vacchi, A.
    Vannuccini, E.
    Vasilyev, G. I.
    Castellini, G.
    Cattaneo, P. W.
    Cumani, P.
    Dedenko, G. L.
    Dogiel, V. A.
    De Donato, C.
    Hnatyk, B. I.
    Gorbunov, M. S.
    Gusakov, Y. V.
    Zampa, N.
    Zverev, V. G.
    Zirakashvili, V. N.
    Kadilin, V. V.
    Kaplin, V. A.
    Kaplun, A. A.
    Korepanov, V. E.
    Larsson, Josefin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Leonov, A. A.
    Loginov, V. A.
    Longo, F.
    Maestro, P.
    Marrocchesi, P. S.
    Mikhailov, V. V.
    Mocchiutti, E.
    Moiseev, A. A.
    Mori, N.
    Moskalenko, I. V.
    Naumov, P. Y.
    Papini, P.
    Picozza, P.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Popov, A. V.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Rappoldi, A.
    Ricciarini, S.
    Runtso, M. F.
    Serdin, O. V.
    Sparvoli, R.
    Spillantini, P.
    Suchkov, S. I.
    Tavani, M.
    Taraskin, A. A.
    Tiberio, A.
    Tyurin, E. M.
    Ulanov, M. V.
    Fuglesang, Christer
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Kheymits, M. D.
    Yurkin, Y. T.
    The GAMMA-400 experiment: Status and prospects2015Inngår i: Bulletin of the Russian Academy of Sciences: Physics, ISSN 1062-8738, Vol. 79, nr 3, s. 417-420Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The development of the GAMMA-400 γ-ray telescope continues. The GAMMA-400 is designed to measure fluxes of γ-rays and the electron-positron cosmic-ray component possibly associated with annihilation or decay of dark matter particles; and to search for and study in detail discrete γ-ray sources, to measure the energy spectra of Galactic and extragalactic diffuse γ-rays, and to study γ-ray bursts and γ-rays from the active Sun. The energy range for measuring γ-rays and electrons (positrons) is from 100 MeV to 3000 GeV. For 100-GeV γ-rays, the γ-ray telescope has an angular resolution of ∼0.01°, an energy resolution of ∼1%, and a proton rejection factor of ∼5 × 105. The GAMMA-400 will be installed onboard the Russian Space Observatory.

  • 836. Topchiev, N. P.
    et al.
    Larsson, Josefin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden.
    Zverev, V. G.
    et al.,
    The GAMMA-400 gamma-ray telescope for precision gamma-ray emission investigations2016Inngår i: INTERNATIONAL CONFERENCE ON PARTICLE PHYSICS AND ASTROPHYSICS (ICPPA-2015), PTS 1-4, Institute of Physics (IOP), 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The GAMMA-400 gamma-ray telescope with excellent angular and energy resolutions is designed to search for signatures of dark matter in the fluxes of gamma-ray emission and electrons + positrons. Precision investigations of gamma-ray emission from Galactic Center, Crab, Vela, Cygnus, Geminga, and other regions will be performed, as well as diffuse gamma-ray emission, along with measurements of high-energy electron + positron and nuclei fluxes. Furthermore, it will study gamma-ray bursts and gamma-ray emission from the Sun during periods of solar activity. The GAMMA-400 energy range is expected to be from similar to 20 MeV up to TeV energies for gamma rays, up to 10 TeV for electrons + positrons, and up to 10(15) eV for cosmic-ray nuclei. For 100-GeV gamma rays, the GAMMA-400 angular resolution is similar to 0.01 degrees and energy resolution is similar to 1%; the proton rejection factor is similar to 5x10(5). GAMMA-400 will be installed onboard the Russian space observatory.

  • 837. Topchiev, N. P.
    et al.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden.
    Zverev, V. G.
    et al.,
    Perspectives of the GAMMA-400 space observatory for high-energy gamma rays and cosmic rays measurements2016Inngår i: INTERNATIONAL CONFERENCE ON PARTICLE PHYSICS AND ASTROPHYSICS (ICPPA-2015), PTS 1-4, Institute of Physics (IOP), 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The GAMMA-400 gamma-ray telescope is intended to measure the fluxes of gamma-rays and cosmic-ray electrons and positrons in the energy range from 100 MeV to several TeV. Such measurements concern the following scientific tasks: investigation of point sources of gamma-rays, studies of the energy spectra of Galactic and extragalactic diffuse emission, studies of gamma-ray bursts and gamma-ray emission from the Sun, as well as high precision measurements of spectra of high-energy electrons and positrons. Also the GAMMA-400 instrument provides the possibility for protons and nuclei measurements up to knee. But the main goal for the GAMMA-400 mission is to perform a sensitive search for signatures of dark matter particles in high-energy gamma-ray emission. To fulfill these measurements the GAMMA-400 gamma-ray telescope possesses unique physical characteristics in comparison with previous and present experiments. The major advantage of the GAMMA-400 instrument is excellent angular and energy resolution for gamma-rays above 10 GeV. The GAMMA-400 experiment will be installed onboard of the Navigator space platform, manufactured by the NPO Lavochkin Association. The expected orbit will be a highly elliptical orbit (with apogee 300.000 km and perigee 500 km) with 7 days orbital period. An important profit of such an orbit is the fact that the full sky coverage will always be available for gamma ray astronomy.

  • 838.
    Tremblin, Pascal
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. University of Exeter, United Kingdom .
    Anderson, L. D.
    Didelon, P.
    Raga, Alejandro C.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Minier, V.
    Ntormousi, E.
    Pettitt, A.
    Pinto, C.
    Samal, M. R.
    Schneider, N.
    Zavagno, A.
    Age, size, and position of H II regions in the Galaxy Expansion of ionized gas in turbulent molecular clouds2014Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 568, s. A4-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aims. This work aims to improve the current understanding of the interaction between H II regions and turbulent molecular clouds. We propose a new method to determine the age of a large sample of OB associations by investigating the development of their associated H II regions in the surrounding turbulent medium. Methods. Using analytical solutions, one-dimensional (ID), and three-dimensional (3D) simulations, we constrained the expansion of the ionized bubble depending on the turbulence level of the parent molecular cloud. A grid of 1D simulations was then computed in order to build isochrone curves for Hit regions in a pressure size diagram. This grid of models allowed us to date a large sample of OB associations that we obtained from the Hit Region Discovery Survey (HRDS). Results. Analytical solutions and numerical simulations showed that the expansion of H II regions is slowed down by the turbulence up to the point where the pressure of the ionized gas is in a quasi-equilibrium with the turbulent ram pressure. Based on this result, we built a grid of ID models of the expansion of Hit regions in a profile based on Larson's laws. We take the 3D turbulence into account with an effective ID temperature profile. The ages estimated by the isochrones of this grid agree well with literature values of well known regions such as Rosette, RCW 36, RCW 79, and M 16. We thus propose that this method can be used to find ages of young OB associations through the Galaxy and also in nearby extra-galactic sources.

  • 839. Troja, E
    et al.
    Piro, L
    Vasileiou, V
    Omodei, N
    Burgess, James Michael
    University of Alabama in Huntsville, United States.
    Swift and Fermi observations of X-ray flares: the case of Late Internal Shock2015Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 803, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Simultaneous Swift and Fermi observations of gamma-ray bursts (GRBs) offer a unique broadband view of their afterglow emission, spanning more than 10 decades in energy. We present the sample of X-ray flares observed by both Swift and Fermi during the first three years of Fermi operations. While bright in the X-ray band, X-ray flares are often undetected at lower (optical), and higher (MeV to GeV) energies. We show that this disfavors synchrotron self-Compton processes as the origin of the observed X-ray emission. We compare the broadband properties of X-ray flares with the standard late internal shock model, and find that in this scenario, X-ray flares can be produced by a late-time relativistic (Γ > 50) outflow at radii R ∼ 1013-1014 cm. This conclusion holds only if the variability timescale is significantly shorter than the observed flare duration, and implies that X-ray flares can directly probe the activity of the GRB central engine.

  • 840. Tsygankov, S. S.
    et al.
    Doroshenko, V.
    Lutovinov, A. A.
    Mushtukov, A. A.
    Poutanen, Juri
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    SMC X-3: The closest ultraluminous X-ray source powered by a neutron star with non-dipole magnetic field2017Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, artikkel-id A39Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aims. The magnetic field of accreting neutron stars determines their overall behavior including the maximum possible luminosity. Some models require an above-average magnetic field strength (≥ 1013 G) in order to explain super-Eddington mass accretion rate in the recently discovered class of pulsating ultraluminous X-ray sources (ULX). The peak luminosity of SMC X-3 during its major outburst in 2016-2017 reached ~2.5 × 1039 erg s-1 comparable to that in ULXs thus making this source the nearest ULX-pulsar. Determination of the magnetic field of SMC X-3 is the main goal of this paper. Methods. SMC X-3 belongs to the class of transient X-ray pulsars with Be optical companions, and exhibited a giant outburst in July 2016-March 2017. The source has been observed over the entire outburst with the Swift/XRT and Fermi/GBM telescopes, as well as the NuSTAR observatory. Collected data allowed us to estimate the magnetic field strength of the neutron star in SMC X-3 using several independent methods. Results. Spin evolution of the source during and between the outbursts, and the luminosity of the transition to the so-called propeller regime in the range of (0.3-7) × 1035 erg s-1 imply a relatively weak dipole field of (1-5) × 1012 G. On the other hand, there is also evidence for a much stronger field in the immediate vicinity of the neutron star surface. In particular, transition from super- to sub-critical accretion regime associated with the cease of the accretion column and very high peak luminosity favor a field that is an order of magnitude stronger. This discrepancy makes SMC X-3 a good candidate for possessing significant non-dipolar components of the field, and an intermediate source between classical X-ray pulsars and accreting magnetars which may constitute an appreciable fraction of ULX population.

  • 841. Tsygankov, S. S.
    et al.
    Lutovinov, A. A.
    Doroshenko, V.
    Mushtukov, A. A.
    Suleimanov, V.
    Poutanen, Juri
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Propeller effect in two brightest transient X-ray pulsars: 4U 0115+63 and v 0332+532016Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 593, artikkel-id A16Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aims. We present the results of the monitoring programmes performed with the Swift/XRT telescope and aimed specifically to detect an abrupt decrease of the observed flux associated with a transition to the propeller regime in two well-known X-ray pulsars 4U 0115+63 and V 0332+53. Methods. Both sources form binary systems with Be optical companions and undergo so-called giant outbursts every 3-4 years. The current observational campaigns were performed with the Swift/XRT telescope in the soft X-ray band (0.5-10 keV) during the declining phases of the outbursts exhibited by both sources in 2015. Results. The transitions to the propeller regime were detected at the threshold luminosities of (1.4 ± 0.4) × 1036 erg s-1 and (2.0 ± 0.4) × 1036 erg s-1 for 4U 0115+63 and V 0332+53, respectively. Spectra of the sources are shown to be significantly softer during the low state. In both sources, the accretion at rates close to the aforementioned threshold values briefly resumes during the periastron passage following the transition into the propeller regime. The strength of the dipole component of the magnetic field required to inhibit the accretion agrees well with estimates based on the position of the cyclotron lines in their spectra, thus excluding presence of a strong multipole component of the magnetic field in the vicinity of the neutron star.

  • 842. Tsygankov, S. S.
    et al.
    Mushtukov, A. A.
    Suleimanov, V. F.
    Doroshenko, V.
    Abolmasov, P. K.
    Lutovinov, A. A.
    Poutanen, Juri
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. University of Turku, Finland.
    Stable accretion from a cold disc in highly magnetized neutron stars2017Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 608, artikkel-id A17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aims. The aim of this paper is to investigate the transition of a strongly magnetized neutron star into the accretion regime with very low accretion rate.& para;& para;Methods. For this purpose, we monitored the Be-transient X-ray pulsar GRO J1008-57 throughout a full orbital cycle. The current observational campaign was performed with the Swift/XRT telescope in the soft X-ray band (0.5-10 keV) between two subsequent Type I outbursts in January and September 2016.& para;& para;Results. The expected transition to the propeller regime was not observed. However, transitions between different regimes of accretion were detected. In particular, after an outburst, the source entered a stable accretion state characterised by an accretion rate of similar to 10(14)-10(15) g s(-1). We associate this state with accretion from a cold (low-ionised) disc of temperature below similar to 6500 K. We argue that a transition to this accretion regime should be observed in all X-ray pulsars that have a certain combination of the rotation frequency and magnetic field strength. The proposed model of accretion from a cold disc is able to explain several puzzling observational properties of X-ray pulsars.

  • 843. Tsygankov, Sergey S.
    et al.
    Lutovinov, Alexander A.
    Krivonos, Roman A.
    Molkov, Sergey V.
    Jenke, Peter J.
    Finger, Mark H.
    Poutanen, Juri
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. University of Turku, Finland.
    NuSTAR discovery of a cyclotron absorption line in the transient X-ray pulsar 2S 1553-5422016Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 457, nr 1, s. 258-266Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the results of a spectral and timing analysis of the poorly studied transient X-ray pulsar 2S 1553-542 using data collected with the NuSTAR and Chandra observatories and the Fermi/GBM instrument during an outburst in 2015. The properties of the source at high energies (>30 keV) are studied for the first time and the sky position has been essentially improved. The source broad-band spectrum has a quite complicated shape and can be reasonably described by a composite model with two continuum components - a blackbody emission with the temperature about 1 keV at low energies and a power law with an exponential cut-off at high energies. Additionally, an absorption feature at similar to 23.5 keV is discovered both in phase-averaged and phase-resolved spectra and interpreted as the cyclotron resonance scattering feature corresponding to the magnetic field strength of the neutron star B similar to 3 x 10(12) G. Based on the Fermi/ GBM data, the orbital parameters of the system were substantially improved, which allowed us to determine the spin period of the neutron star P = 9.27880(3) s and a local spin-up. (P) over dot similar or equal to -7.5 x 10(-10) s s(-1) due to the mass accretion during the NuSTAR observations. Assuming accretion from the disc and using standard torque models, we estimated the distance to the system as d = 20 +/- 4 kpc.

  • 844. Usoskin, I. G.
    et al.
    Kovaltsov, G. A.
    Adriani, O.
    Barbarino, G. C.
    Bazilevskaya, G. A.
    Bellotti, R.
    Boezio, M.
    Bogomolov, E. A.
    Bongi, M.
    Bonvicini, V.
    Bottai, S.
    Bruno, A.
    Cafagna, F.
    Campana, D.
    Carbone, R.
    Carlson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Casolino, M.
    Castellini, G.
    De Donato, C.
    De Santis, C.
    De Simone, N.
    Di Felice, V.
    Format, V.
    Galper, A. M.
    Karelin, A. V.
    Koldashov, S. V.
    Koldobskiy, S.
    Krutkov, S. Y.
    Kvashnin, A. N.
    Leonov, A.
    Malakhov, V.
    Marcelli, L.
    Martucci, M.
    Mayorov, A. G.
    Menn, W.
    Merge, M.
    Mikhailov, V. V.
    Mocchiutti, E.
    Monaco, A.
    Mori, N.
    Munini, R.
    Osteria, G.
    Palma, F.
    Panico, B.
    Papini, P.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Picozza, P.
    Pizzolotto, C.
    Ricci, M.
    Ricciarini, S. B.
    Rossetto, Laura
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sarkar, R.
    Scotti, V.
    Simon, M.
    Sparvoli, R.
    Spillantini, P.
    Stozhkov, Y. I.
    Vacchi, A.
    Vannuccini, E.
    Vasilye, G. I.
    Voronov, S. A.
    Yurkin, Y. T.
    Zampa, G.
    Zampa, N.
    Zverev, V. G.
    Force-field parameterization of the galactic cosmic ray spectrum: Validation for Forbush decreases2015Inngår i: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 55, nr 12, s. 2940-2945Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A useful parametrization of the energy spectrum of galactic cosmic rays (GCR) near Earth is offered by the so-called force-field model which describes the shape of the entire spectrum with a single parameter, the modulation potential. While the usefulness of the force-field approximation has been confirmed for regular periods of solar modulation, it was not tested explicitly for disturbed periods, when GCR are locally modulated by strong interplanetary transients. Here we use direct measurements of protons and alpha-particles performed by the PAMELA space-borne instrument during December 2006, including a major Forbush decrease, in order to directly test the validity of the force-field parameterization. We conclude that (1) The force-field parametrization works very well in describing the energy spectra of protons and alpha-particles directly measured by PAMELA outside the Earths atmosphere; (2) The energy spectrum of GCR can be well parameterized by the force-field model also during a strong Forbush decrease; (3) The estimate of the GCR modulation parameter, obtained using data from the world-wide neutron monitor network, is in good agreement with the spectra directly measured by PAMELA during the studied interval. This result is obtained on the basis of a single event analysis, more events need to be analyzed.

  • 845.
    Vagnozzi, Sunny
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Oskar Klein Ctr Cosmoparticle Phys, Dept Phys, Alballova Univ Ctr, Roslagstullsbacken 21A, SE-10691 Stockholm, SwedenStockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.;Univ Cambridge, Kavh Inst Cosmol KICC, Madingley Rd, Cambridge CB3 0HA, England.;Univ Cambridge, Inst Astron, Madingley Rd, Cambridge CB3 0HA, England..
    Visinelli, Luca
    Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.;Uppsala Univ, Dept Phys & Astron, Lagerhyddsvagen 1, S-75120 Uppsala, Sweden.;Univ Amsterdam, Gravitat Astroparticle Phys Amsterdam GRAPPA, Inst Theoret Phys Amsterdam, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands.;Univ Amsterdam, Delta Inst Theoret Phys, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands..
    Hunting for extra dimensions in the shadow of M872019Inngår i: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 100, nr 2, artikkel-id 024020Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Event Horizon Telescope has recently provided the first image of the dark shadow around the supermassive black hole M87*. The observation of a highly circular shadow provides strong limits on deviations of M87*'s quadrupole moment from the Kerr value. We show that the absence of such a deviation can be used to constrain the physics of extra dimensions of spacetime. Focusing on the Randall-Sundrum AdS(5) brane-world scenario, we show that the observation of M87*'s dark shadow sets the limit l less than or similar to 170 AU, where l is the AdS(5) curvature radius. This limit is among the first quantitative constraints on exotic physics obtained from the extraordinary first ever image of the dark shadow of a black hole.

  • 846.
    Valan, Vlasta
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Thermal components in the early X-ray afterglow of gamma-ray bursts2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Gamma-ray bursts (GRBs) are still puzzling scientists even 40 years after their discovery. Questions concerning the nature of the progenitors, the connection with supernovae and the origin of the high-energy emission are still lacking clear answers. Today, it is known that there are two populations of GRBs: short and long. It is also known that long GRBs are connected to supernovae (SNe). The emission observed from GRBs can be divided into two phases: the prompt emission and the afterglow. This thesis presents spectral analysis of the early X-ray afterglow of GRBs observed by the {\it Swift} satellite. For the majority of GRBs the early X-ray afterglows are well described by an absorbed power-law model. However, there exists a number of cases where this power-law component fails in fully describing the observed spectra and an additional blackbody component is needed. In the paper at the end of this thesis, a time-resolved spectral analysis of 74 GRBs observed by the X-ray telescope on board {\it Swift} is presented. Each spectrum is fitted with a power-law and a power-law plus blackbody model. The significance of the added thermal component is then assessed using Monte Carlo simulations. Six new cases of GRBs with thermal components in their spectra are presented, alongside three previously reported cases. The results show that a cocoon surrounding the jet is the most likely explanation for the thermal emission observed in the majority of GRBs. In addition, the observed narrow span in radii points to these GRBs being produced in similar environments.

    Fulltekst (pdf)
    fulltext
  • 847.
    Valan, Vlasta
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Larsson, Josefin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ahlgren, Björn
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Thermal components in the early X-ray afterglows of GRBs: likely cocoon emission and constraints on the progenitorsManuskript (preprint) (Annet vitenskapelig)
  • 848.
    Valan, Vlasta
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Larsson, Josefin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ahlgren, Björn
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Thermal components in the early X-ray afterglows of GRBs: likely cocoon emission and constraints on the progenitorsManuskript (preprint) (Annet vitenskapelig)
    Fulltekst (pdf)
    fulltext
  • 849.
    Vallini, Livia
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Pallottini, A.
    Ferrara, A.
    Gallerani, S.
    Sobacchi, E.
    Behrens, C.
    CO line emission from galaxies in the Epoch of Reionization2018Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 473, nr 1, s. 271-285Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the CO line luminosity (L-CO), the shape of the CO spectral line energy distribution (SLED), and the value of the CO-to-H-2 conversion factor in galaxies in the Epoch of Reionization (EoR). For this aim, we construct a model that simultaneously takes into account the radiative transfer and the clumpy structure of giant molecular clouds (GMCs) where the CO lines are excited. We then use it to post-process state-of-the-art zoomed, high resolution (30 pc), cosmological simulation of a main-sequence (M-* approximate to 10(10) M-circle dot, SFR approximate to 100M(circle dot) yr(-1)) galaxy, 'Althaea', at z approximate to 6. We find that the CO emission traces the inner molecular disc (r approximate to 0.5 kpc) of Althaea with the peak of the CO surface brightness co-located with that of the [C-II] 158 mu m emission. Its LCO(1-0) = 10(4.85) L-circle dot is comparable to that observed in local galaxies with similar stellar mass. The high (Sigma(gas) approximate to 220M(circle dot) pc(-2)) gas surface density in Althaea, its large Mach number (M approximate to 30) and the warm kinetic temperature (T-k approximate to 45 K) of GMCs yield a CO SLED peaked at the CO(7-6) transition, i.e. at relatively high-J and a CO-to-H-2 conversion factor alpha(CO) approximate to 1.5M(circle dot) (K km s(-1) pc(2))(-1) lower than that of the Milky Way. The Atacama Large Millimeter/submillimeter Array observing time required to detect (resolve) at 5 sigma the CO(7-6) line from galaxies similar to Althaea is approximate to 13 h (approximate to 38 h).

  • 850. Valtonen, Mauri
    et al.
    Nurmi, Pasi
    Zheng, Jia-Qing
    Cucinotta, Francis A.
    Wilson, John W.
    Horneck, Gerda
    Lindegren, Lennart
    Melosh, Jay
    Rickman, Hans
    Mileikowsky, Curt
    KTH, Skolan för teknikvetenskap (SCI).
    NATURAL TRANSFER OF VIABLE MICROBES IN SPACE FROM PLANETS IN EXTRA-SOLAR SYSTEMS TO A PLANET IN OUR SOLAR SYSTEM AND VICE VERSA2009Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 690, nr 1, s. 210-215Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate whether it is possible that viable microbes could have been transported to the Earth from planets in extra-solar systems by means of natural vehicles such as ejecta expelled by comets or asteroid impacts on such planets. The probabilities of close encounters with other solar systems are taken into account as well as the limitations of bacterial survival times inside ejecta in space, caused by radiation and DNA decay. The conclusion is that no potentially DNA/RNA life-carrying ejecta from another solar system in the general Galactic star field landed on the Earth before life already existed on the Earth, even if the microbial survival time in space is as long as tens of millions of years. However, if the Sun formed initially as a part of a star cluster, as is commonly assumed, we cannot rule out the possibility of transfer of life from one of the sister systems to us. Likewise, there is a possibility that some extra-solar planets carry life that originated in our solar system. It will be of great interest to identify the members of the Sun's birth cluster of stars and study them for evidence of planets and life on the planets. The former step may be accomplished by the GAIA mission, the latter step by the SIM and DARWIN missions. Therefore it may not be too long until we have experimental knowledge to answer the question of whether the natural transfer of life from one solar system to another has actually taken place.

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