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  • 1. Abellán, F. J.
    et al.
    Indebetouw, R.
    Marcaide, J. M.
    Gabler, M.
    Fransson, C.
    Spyromilio, J.
    Burrows, D. N.
    Chevalier, R.
    Cigan, P.
    Gaensler, B. M.
    Gomez, H. L.
    Janka, H. -T
    Kirshner, R.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lundqvist, P.
    Matsuura, M.
    McCray, R.
    Ng, C. -Y
    Park, S.
    Roche, P.
    Staveley-Smith, L.
    Loon, J. T. V.
    Wheeler, J. C.
    Woosley, S. E.
    Very Deep inside the SN 1987A Core Ejecta: Molecular Structures Seen in 3D2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 842, no 2, article id L24Article in journal (Refereed)
    Abstract [en]

    Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outward through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Atacama Large Millimeter/submillimeter Array are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks ("nickel heating"). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained.

  • 2.
    Ahlgren, Björn
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oscar Klein Centre, Sweden.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oscar Klein Centre, Sweden.
    Nymark, Tanja
    KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Education and Communication in Engineering Science (ECE), Learning. Oscar Klein Centre, Sweden.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Pe'er, A.
    Confronting GRB prompt emission with a model for subphotospheric dissipation2015In: Monthly Notices of the Royal Astronomical Society: Letters, ISSN 1745-3925, Vol. 454, no 1, p. L31-L35Article in journal (Refereed)
    Abstract [en]

    The origin of the prompt emission in gamma-ray bursts (GRBs) is still an unsolved problem and several different mechanisms have been suggested. Here, we fit Fermi GRB data with a photospheric emission model which includes dissipation of the jet kinetic energy below the photosphere. The resulting spectra are dominated by Comptonization and contain no significant contribution from synchrotron radiation. In order to fit to the data, we span a physically motivated part of the model's parameter space and create DREAM (Dissipation with Radiative Emission as A table Model), a table model for XSPEC. We show that this model can describe different kinds of GRB spectra, including GRB 090618, representing a typical Band function spectrum, and GRB 100724B, illustrating a double peaked spectrum, previously fitted with a Band+blackbody model, suggesting they originate from a similar scenario. We suggest that the main difference between these two types of bursts is the optical depth at the dissipation site.

  • 3.
    Alp, Dennis
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics.
    Fransson, Claes
    Stockholm Univ, Dept Astron, Oskar Klein Ctr, AlbaNova, SE-10691 Stockholm, Sweden..
    Gabler, Michael
    Max Planck Inst Astrophys, Karl Schwarzschild Str 1, D-85748 Garching, Germany..
    Wongwathanarat, Annop
    Max Planck Inst Astrophys, Karl Schwarzschild Str 1, D-85748 Garching, Germany..
    Janka, Hans-Thomas
    Max Planck Inst Astrophys, Karl Schwarzschild Str 1, D-85748 Garching, Germany..
    X-Ray Absorption in Young Core-collapse Supernova Remnants2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 864, no 2, article id 175Article in journal (Refereed)
    Abstract [en]

    The material expelled by core-collapse supernova (SN) explosions absorbs X-rays from the central regions. We use SN models based on three-dimensional neutrino-driven explosions to estimate optical depths to the center of the explosion, compare different progenitor models, and investigate the effects of explosion asymmetries. The optical depths below 2 keV for progenitors with a remaining hydrogen envelope are expected to be high during the first century after the explosion due to photoabsorption. A typical optical depth is 100 t(4)(-2 )E(-2), where t(4) is the time since the explosion in units of 10,000 days (similar to 27 years) and E is the energy in units of keV. Compton scattering dominates above 50 keV, but the scattering depth is lower and reaches unity at similar to 1000 days at 1 MeV. The optical depths are approximately an order of magnitude lower for hydrogen-stripped progenitors. The metallicity of the SN ejecta is much higher than that in the interstellar medium, which enhances photoabsorption and makes absorption edges stronger. These results are applicable to young SN remnants in general, but we explore the effects on observations of SN 1987A and the compact object in Cas A in detail. For SN 1987A, the absorption is high and the X-ray upper limits of similar to 100 L-circle dot on a compact object are approximately an order of magnitude less constraining than previous estimates using other absorption models. The details are presented in an accompanying paper. For the central compact object in Cas A, we find no significant effects of our more detailed absorption model on the inferred surface temperature.

  • 4.
    Alp, Dennis
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics.
    Fransson, Claes
    Stockholm Univ, Dept Astron, Oskar Klein Ctr, AlbaNova, SE-10691 Stockholm, Sweden..
    Indebetouw, Remy
    Natl Radio Astron Observ, 520 Edgemont Rd, Charlottesville, VA 22903 USA.;Univ Virginia, 520 Edgemont Rd, Charlottesville, VA 22903 USA..
    Jerkstrand, Anders
    Max Planck Inst Astrophys, Karl Schwarzschild Str 1, D-85748 Garching, Germany..
    Ahola, Antero
    Univ Turku, Dept Phys & Astron, Tuorla Observ, Vaisalantie 20, FI-21500 Piikkio, Finland..
    Burrows, David
    Penn State Univ, Dept Astron & Astrophys, 525 Davey Lab, University Pk, PA 16802 USA..
    Challis, Peter
    Harvard Smithsonian Ctr Astrophys, 60 Garden St, Cambridge, MA 02138 USA..
    Cigan, Phil
    Cardiff Univ, Sch Phys & Astrophys, Queens Bldg, Cardiff CF24 3AA, S Glam, Wales..
    Cikota, Aleksandar
    European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Kirshner, Robert P.
    Harvard Smithsonian Ctr Astrophys, 60 Garden St, Cambridge, MA 02138 USA.;Gordon & Betty Moore Fdn, 1661 Page Mill Rd, Palo Alto, CA 94304 USA..
    van Loon, Jacco Th.
    Keele Univ, Lennard Jones Labs, Keele ST5 5BG, Staffs, England..
    Mattila, Seppo
    Univ Turku, Dept Phys & Astron, Tuorla Observ, Vaisalantie 20, FI-21500 Piikkio, Finland..
    Ng, C. -Y
    Park, Sangwook
    Univ Texas Arlington, Dept Phys, Box 19059,108 Sci Hall, Arlington, TX 76019 USA..
    Spyromilio, Jason
    European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Woosley, Stan
    Univ Calif Santa Cruz, Dept Astron & Astrophys, Santa Cruz, CA 95064 USA..
    Baes, Maarten
    Univ Ghent, Sterrenkundig Observ, Krijgslaan 281 S9, B-9000 Ghent, Belgium..
    Bouchet, Patrice
    Univ Paris Saclay, CEA, IRFU, F-91191 Gif Sur Yvette, France.;Univ Paris Diderot, CNRS, AIM, F-91191 Gif Sur Yvette, France..
    Chevalier, Roger
    Univ Virginia, Dept Astron, POB 400325, Charlottesville, VA 22904 USA..
    Frank, Kari A.
    Northwestern Univ, CIERA, 2145 Sheridan Rd, Evanston, IL 60208 USA..
    Gaensler, B. M.
    Dunlap Inst Astron & Astrophys, 50 St George St, Toronto, ON M5S 3H4, Canada..
    Gomez, Haley
    Cardiff Univ, Sch Phys & Astrophys, Queens Bldg, Cardiff CF24 3AA, S Glam, Wales..
    Janka, Hans-Thomas
    Max Planck Inst Astrophys, Karl Schwarzschild Str 1, D-85748 Garching, Germany..
    Leibundgut, Bruno
    European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Lundqvist, Peter
    Stockholm Univ, Dept Astron, Oskar Klein Ctr, AlbaNova, SE-10691 Stockholm, Sweden..
    Marcaide, Jon
    Univ Valencia, Dept Astron & Astrofis, Dr Moliner 50, E-46100 Burjassot, Spain..
    Matsuura, Mikako
    Cardiff Univ, Sch Phys & Astrophys, Queens Bldg, Cardiff CF24 3AA, S Glam, Wales..
    Sollerman, Jesper
    Stockholm Univ, Dept Astron, Oskar Klein Ctr, AlbaNova, SE-10691 Stockholm, Sweden..
    Sonneborn, George
    NASA, Goddard Space Flight Ctr, Lab Observat Cosmol, Code 665, Greenbelt, MD 20771 USA..
    Staveley-Smith, Lister
    Univ Western Australia, ICRAR, 35 Stirling Hwy, Crawley, WA 6009, Australia..
    Zanardo, Giovanna
    Univ Western Australia, ICRAR, 35 Stirling Hwy, Crawley, WA 6009, Australia..
    Gabler, Michael
    Max Planck Inst Astrophys, Karl Schwarzschild Str 1, D-85748 Garching, Germany..
    Taddia, Francesco
    Stockholm Univ, Dept Astron, Oskar Klein Ctr, AlbaNova, SE-10691 Stockholm, Sweden..
    Wheeler, J. Craig
    Univ Texas Austin, Dept Astron, RLM 15308, Austin, TX 78712 USA.;Univ Texas Austin, McDonald Observ, Austin, TX 78712 USA..
    The 30 Year Search for the Compact Object in SN 1987A2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 864, no 2, article id 174Article in journal (Refereed)
    Abstract [en]

    Despite more than 30 years of searching, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy (0.1 x 10(-26) erg s(-1) cm(-2) Hz(-1)) at 213 GHz, 1 L-circle dot (6 x 10(-29) erg s(-1) cm(-2) Hz(-1)) in the optical if our line of sight is free of ejecta dust, and 10(36) erg s(-1) (2 x 10(-30) erg s(-1) cm(-2) Hz(-1) ) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven SN explosion models. The allowed bolometric luminosity of the compact object is 22 L-circle dot if our line of sight is free of ejecta dust, or 138L(circle dot) if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star (NS) to <4-8 MK and do not exclude models, which typically are in the range 3-4 MK. For the simplest accretion model, the accretion rate for an efficiency 77 is limited to <10(-11) eta(-1) M-circle dot yr(-1), which excludes most predictions. For pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (B) for a given spin period (P) is B less than or similar to 10(14) P-2 G s(-2), which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting NS, which may appear as a region of higher-temperature ejecta dust emission.

  • 5. D'Ammando, F.
    et al.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Orienti, M.
    Raiteri, C. M.
    Angelakis, E.
    Carraminana, A.
    Carrasco, L.
    Drake, A. J.
    Fuhrmann, L.
    Giroletti, M.
    Hovatta, T.
    Max-Moerbeck, W.
    Porras, A.
    Readhead, A. C. S.
    Recillas, E.
    Richards, J. L.
    Multiwavelength observations of the gamma-ray-emitting narrow-line Seyfert 1 PMN J0948+0022 in 20112014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 438, no 4, p. 3521-3534Article in journal (Refereed)
    Abstract [en]

    We report on radio-to-gamma-ray observations during 2011 May-September of PMN J0948+0022, the first narrow-line Seyfert 1 (NLSy1) galaxy detected in gamma-rays by Fermi-Large Area Telescope. Strong variability was observed in gamma-rays, with two flaring periods peaking on 2011 June 20 and July 28. The variability observed in optical and near-infrared seems to have no counterpart in gamma-rays. This different behaviour could be related to a bending and inhomogeneous jet or a turbulent extreme multicell scenario. The radio spectra showed a variability pattern typical of relativistic jets. The XMM spectrum shows that the emission from the jet dominates above similar to 2 keV, while a soft X-ray excess is evident in the low-energy part of the X-ray spectrum. Models where the soft emission is partly produced by blurred reflection or Comptonization of the thermal disc emission provide good fits to the data. The X-ray spectral slope is similar to that found in radio-quiet NLSy1, suggesting that a standard accretion disc is present, as expected from the high accretion rate. Except for the soft X-ray excess, unusual in jet-dominated active galactic nuclei, PMN J0948+0022, shows all characteristics of the blazar class.

  • 6. D’Ammando, F.
    et al.
    Orienti, M.
    Finke, J.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Giroletti, M.
    Gamma-ray emitting narrow-line Seyfert 1 galaxies. New discoveries and open questions2014In: Proceedings of the International Astronomical Union, ISSN 1743-9213, E-ISSN 1743-9221, Vol. 9, no S304, p. 140-143Article in journal (Refereed)
    Abstract [en]

    The discovery of γ-ray emission from 5 radio-loud narrow-line Seyfert 1 galaxies revealed the presence of a possible emerging third class of AGNs with relativistic jets, in addition to blazars and radio galaxies. The existence of relativistic jets also in this subclass of Seyfert galaxies opened an unexplored research space for our knowledge of the radio-loud AGNs. Here, we discuss the radio-to-γ-rays properties of the γ-ray emitting narrow-line Seyfert 1 galaxies, also in comparison with the blazar scenario.

  • 7. D'Ammando, F.
    et al.
    Orienti, M.
    Finke, J.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Giroletti, M.
    Relativistic jets in narrow-line Seyfert 1 galaxies. New discoveries and open questions2013In: EPJ Web of Conferences: The Innermost Regions of Relativistic Jets and Their Magnetic Fields, EDP Sciences, 2013, p. 05006-Conference paper (Refereed)
    Abstract [en]

    Before the launch of the Fermi satellite only two classes of AGNs were known to produce relativistic jets and thus emit up to the γ-ray energy range: blazars and radio galaxies, both hosted in giant elliptical galaxies. The first four years of observations by the Large Area Telescope on board Fermi confirmed that these two are the most numerous classes of identified sources in the extragalactic γ-ray sky, but the discovery of γ-ray emission from 5 radio-loud narrow-line Seyfert 1 galaxies revealed the presence of a possible emerging third class of AGNs with relativistic jets. Considering that narrow-line Seyfert 1 galaxies seem to be typically hosted in spiral galaxy, this finding poses intriguing questions about the nature of these objects, the onset of production of relativistic jets, and the cosmological evolution of radio-loud AGN. Here, we discuss the radio-to-γ-rays properties of the γ-ray emitting narrow-line Seyfert 1 galaxies, also in comparison with the blazar scenario.

  • 8. D'Ammando, F.
    et al.
    Orienti, M.
    Finke, J.
    Raiteri, C. M.
    Hovatta, T.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Max-Moerbeck, W.
    Perkins, J.
    Readhead, A. C. S.
    Richards, J. L.
    Beilicke, M.
    Benbow, W.
    Berger, K.
    Bird, R.
    Bugaev, V.
    Cardenzana, J. V.
    Cerruti, M.
    Chen, X.
    Ciupik, L.
    Dickinson, H. J.
    Eisch, J. D.
    Errando, M.
    Falcone, A.
    Finley, J. P.
    Fleischhack, H.
    Fortin, P.
    Fortson, L.
    Furniss, A.
    Gerard, L.
    Gillanders, G. H.
    Griffiths, S. T.
    Grube, J.
    Gyuk, G.
    Håkansson, N.
    Holder, J.
    Humensky, T. B.
    Kar, P.
    Kertzman, M.
    Khassen, Y.
    Kieda, D.
    Krennrich, F.
    Kumar, S.
    Lang, M. J.
    Maier, G.
    McCann, A.
    Meagher, K.
    Moriarty, P.
    Mukherjee, R.
    Nieto, D.
    de Bhroithe, A. O'Faolain
    Ong, R. A.
    Otte, A. N.
    Pohl, M.
    Popkow, A.
    Prokoph, H.
    Pueschel, E.
    Quinn, J.
    Ragan, K.
    Reynolds, P. T.
    Richards, G. T.
    Roache, E.
    Rousselle, J.
    Santander, M.
    Sembroski, G. H.
    Smith, A. W.
    Staszak, D.
    Telezhinsky, I.
    Tucci, J. V.
    Tyler, J.
    Varlotta, A.
    Vassiliev, V. V.
    Wakely, S. P.
    Weinstein, A.
    Welsing, R.
    Williams, D. A.
    Zitzer, B.
    The most powerful flaring activity from the NLSyl PMN J0948+00222015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 446, no 3, p. 2456-2467Article in journal (Refereed)
    Abstract [en]

    We report on multifrequency observations performed during 2012 December-2013 August of the first narrow-line Seyfert 1 galaxy detected in gamma-rays, PMN J0948+0022 (z = 0.5846). A y -ray flare was observed by the Large Area Telescope on board Fermi during 2012 December-2013 January, reaching a daily peak flux in the 0.1-100 GeV energy range of (155 31) x 10 8 ph cm(-2) S-1 on 2013 January 1, corresponding to an apparent isotropic luminosity of similar to 1.5 x 1048 erg s(-1). The y -ray flaring period triggered Swift and Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations in addition to radio and optical monitoring by Owens Valley Radio Observatory, Monitoring Of Jets in Active galactic nuclei with VLBA Experiments, and Catalina Real-time Transient Survey. A strong flare was observed in optical, UV, and X-rays on 2012 December 30, quasi-simultaneously to the y -ray flare, reaching a record flux for this source from optical to y gamma-rays. VERITAS observations at very high energy (E > 100 GeV) during 2013 January 6-17 resulted in an upper limit of F>0.2 Trev < 4.0 x 10(-12) ph cm(-2) s(-1). We compared the spectral energy distribution (SED) of the flaring state in 2013 January with that of an intermediate state observed in 2011. The two SEDs, modelled as synchrotron emission and an external Compton scattering of seed photons from a dust torus, can be modelled by changing both the electron distribution parameters and the magnetic field.

  • 9. D'Ammando, F.
    et al.
    Orienti, M.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Giroletti, M.
    The first gamma-ray detection of the narrow-line Seyfert 1 FBQS J1644+26192015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 452, no 1, p. 520-524Article in journal (Refereed)
    Abstract [en]

    We report the discovery of gamma-ray emission from the narrow-line Seyfert 1 (NLSy1) galaxy FBQS J1644+2619 by the Large Area Telescope on board the Fermi satellite. The Third Fermi LAT Source catalogue reports an unidentified gamma-ray source, detected over the first four years of Fermi operation, 0 degrees.23 from the radio position of the NLSy1. Analysing 76 months of gamma-ray data (2008 August 4-2014 December 31) we are able to better constrain the localization of the gamma-ray source. The new position of the gamma-ray source is 0 degrees.05 from FBQS J1644+2619, suggesting a spatial association with the NLSy1. This is the sixth NLSy1 detected at high significance by Fermi-LAT so far. Notably, a significant increase of activity was observed in gamma-rays from FBQS J1644+2619 during 2012 July-October, and an increase of activity in the V band was detected by the Catalina Real-Time Sky Survey in the same period.

  • 10. D'Ammando, Filippo
    et al.
    Orienti, Monica
    Finke, Justin
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Giroletti, Marcello
    Raiteri, Claudia M.
    A Panchromatic View of Relativistic Jets in Narrow-Line Seyfert 1 Galaxies2016In: Galaxies, E-ISSN 2075-4434, Vol. 4, no 3, article id 11Article in journal (Refereed)
    Abstract [en]

    The discovery by the Large Area Telescope on board Fermi of variable -ray emission from radio-loud narrow-line Seyfert 1 (NLSy1) galaxies revealed the presence of a possible third class of Active Galactic Nuclei (AGN) with relativistic jets in addition to blazars and radio galaxies. Considering that NLSy1 are usually hosted in spiral galaxies, this finding poses intriguing questions about the nature of these objects and the formation of relativistic jets. We report on a systematic investigation of the -ray properties of a sample of radio-loud NLSy1, including the detection of new objects, using 7 years of Fermi-LAT data with the new Pass 8 event-level analysis. In addition we discuss the radio-to-very-high-energy properties of the -ray emitting NLSy1, their host galaxy, and black hole mass in the context of the blazar scenario and the unification of relativistic jets at different scales.

  • 11. France, Kevin
    et al.
    McCray, Richard
    Fransson, Claes
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Frank, Kari A.
    Burrows, David N.
    Challis, Peter
    Kirshner, Robert P.
    Chevalier, Roger A.
    Garnavich, Peter
    Heng, Kevin
    Lawrence, Stephen S.
    Lundqvist, Peter
    Smith, Nathan
    Sonneborn, George
    MAPPING high-velocity Hα and Lyα emission from supernova 1987A2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 801, no 1, article id L16Article in journal (Refereed)
    Abstract [en]

    We present new Hubble Space Telescope images of high-velocity H alpha and Ly alpha emission in the outer debris of SN 1987 A. The Ha images are dominated by emission from hydrogen atoms crossing the reverse shock (RS). For the first time we observe emission from the RS surface well above and below the equatorial. ring (ER), suggesting a bipolar or conical structure perpendicular to the ring plane. Using the H alpha imaging, we measure the mass flux of hydrogen atoms crossing the RS front, in the velocity intervals (-7500 < V-obs < -2800 km s(-1)) and (1000 < V-obs < 7500 km s(-1)), (M)(H) over dot = 1.2 x 10(-3) M-circle dot yr(-1). We also present the first Ly alpha imaging of the whole remnant and new Chandra X-ray observations. Comparing the spatial distribution of the Ly alpha and X-ray emission, we observe that the majority of the high-velocity Ly alpha emission originates interior to the ER. The observed Ly alpha/H alpha photon ratio, < R(L alpha/H alpha)> approximate to 17, is significantly higher than the theoretically predicted ratio of approximate to 5 for neutral atoms crossing the RS front. We attribute this excess to Ly alpha emission produced by X-ray heating of the outer debris. The spatial orientation of the Ly alpha and X-ray emission suggests that X-ray heating of the outer debris is the dominant Ly alpha production mechanism in SN 1987 A at this phase in its evolution.

  • 12. Fransson, Claes
    et al.
    Ergon, Mattias
    Challis, Peter J.
    Chevalier, Roger A.
    France, Kevin
    Kirshner, Robert P.
    Marion, G. H.
    Milisavljevic, Dan
    Smith, Nathan
    Bufano, Filomena
    Friedman, Andrew S.
    Kangas, Tuomas
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Mattila, Seppo
    Benetti, Stefano
    Chornock, Ryan
    Czekala, Ian
    Soderberg, Alicia
    Sollerman, Jesper
    High-density circumstellar interaction in the luminous type IIn SN 2010jl: The first 1100 days2014In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 797, no 2, p. 118-Article in journal (Refereed)
    Abstract [en]

    Hubble Space Telescope and ground-based observations of the Type IIn supernova (SN) 2010jl are analyzed, including photometry and spectroscopy in the ultraviolet, optical, and near-IR bands, 26-1128 days after first detection. At maximum, the bolometric luminosity was similar to 3 x 10(43) erg s(-1) and even at 850 days exceeds 10(42) erg s(-1). A near-IR excess, dominating after 400 days, probably originates in dust in the circumstellar medium (CSM). The total radiated energy is greater than or similar to 6.5x10(50) erg, excluding the dust component. The spectral lines can be separated into one broad component that is due to electron scattering and one narrow with expansion velocity similar to 100 km s(-1) from the CSM. The broad component is initially symmetric around zero velocity but becomes blueshifted after similar to 50 days, while remaining symmetric about a shifted centroid velocity. Dust absorption in the ejecta is unlikely to explain the line shifts, and we attribute the shift instead to acceleration by the SN radiation. From the optical lines and the X-ray and dust properties, there is strong evidence for large-scale asymmetries in the CSM. The ultraviolet lines indicate CNO processing in the progenitor, while the optical shows a number of narrow coronal lines excited by the X-rays. The bolometric light curve is consistent with a radiative shock in an r(-2) CSM with a mass-loss rate of M similar to 0.1 M(circle dot)yr(-1). The total mass lost is greater than or similar to 3 M-circle dot. These properties are consistent with the SN expanding into a CSM characteristic of a luminous blue variable progenitor with a bipolar geometry. The apparent absence of nuclear processing is attributed to a CSM that is still opaque to electron scattering.

  • 13. Fransson, Claes
    et al.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Migotto, Katia
    Pesce, Dominic
    Challis, Peter
    Chevalier, Roger A.
    France, Kevin
    Kirshner, Robert P.
    Leibundgut, Bruno
    Lundqvist, Peter
    McCray, Richard
    Spyromilio, Jason
    Taddia, Francesco
    Jerkstrand, Anders
    Mattila, Seppo
    Smith, Nathan
    Sollerman, Jesper
    Wheeler, J. Craig
    Crotts, Arlin
    Garnavich, Peter
    Heng, Kevin
    Lawrence, Stephen S.
    Panagia, Nino
    Pun, Chun S. J.
    Sonneborn, George
    Sugerman, Ben
    THE DESTRUCTION OF THE CIRCUMSTELLAR RING OF SN 1987A2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 806, no 1, article id L19Article in journal (Refereed)
    Abstract [en]

    We present imaging and spectroscopic observations with Hubble Space Telescope and Very Large Telescope of the ring of SN 1987A from 1994 to 2014. After an almost exponential increase of the shocked emission from the hotspots up to day similar to 8000 (similar to 2009), both this and the unshocked emission are now fading. From the radial positions of the hotspots we see an acceleration of these up to 500-1000 km s(-1), consistent with the highest spectroscopic shock velocities from the radiative shocks. In the most recent observations (2013 and 2014), we find several new hotspots outside the inner ring, excited by either X-rays from the shocks or by direct shock interaction. All of these observations indicate that the interaction with the supernova ejecta is now gradually dissolving the hotspots. We predict, based on the observed decay, that the inner ring will be destroyed by similar to 2025.

  • 14. Fransson, Claes
    et al.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Spyromilio, Jason
    Chevalier, Roger
    Gröningsson, Per
    Jerkstrand, Anders
    Leibundgut, Bruno
    McCray, Richard
    Challis, Peter
    Kirshner, Robert P.
    Kjaer, Karina
    Lundqvist, Peter
    Sollerman, Jesper
    Late spectral evolution of the ejecta and reverse shock in SN 1987a2013In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 768, no 1, p. 88-Article in journal (Refereed)
    Abstract [en]

    We present observations with the Very Large Telescope and Hubble Space Telescope (HST) of the broad emission lines from the inner ejecta and reverse shock of SN 1987A from 1999 February until 2012 January (days 4381-9100 after explosion). We detect broad lines from H alpha, H beta, Mg I], Na I, [O I], [Ca II], and a feature at similar to 9220 angstrom. We identify the latter line with Mg II lambda lambda 9218, 9244, which is most likely pumped by Ly alpha fluorescence. H alpha and H beta both have a centrally peaked component extending to similar to 4500 km s(-1) and a very broad component extending to greater than or similar to 11,000 km s(-1), while the other lines have only the central component. The low-velocity component comes from unshocked ejecta, heated mainly by X-rays from the circumstellar environment, whereas the very broad component comes from faster ejecta passing through the reverse shock, created by the collision with the circumstellar ring. The flux in H alpha from the reverse shock has increased by a factor of four to six from 2000 to 2007. After that there is a tendency of flattening of the light curve, similar to what may be seen in the optical lines from the shocked ring. The core component seen in H alpha, [Ca II], and Mg II has experienced a similar increase, which is consistent with that found from HST photometry. The energy deposition of the external X-rays is calculated using explosion models for SN 1987A and we predict that the outer parts of the unshocked ejecta will continue to brighten because of this. The external X-ray illumination also explains the edge-brightened morphology of the ejecta seen in the HST images. We finally discuss evidence for dust in the ejecta from line asymmetries.

  • 15. Fransson, Claes
    et al.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Spyromilio, Jason
    Leibundgut, Bruno
    McCray, Richard
    Jerkstrand, Anders
    DISCOVERY OF MOLECULAR HYDROGEN IN SN 1987A2016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 821, no 1, article id L5Article in journal (Refereed)
    Abstract [en]

    Both CO and SiO have been observed at early and late phases in SN 1987A. H-2 was predicted to form at roughly the same time as these molecules, but was not detected at early epochs. Here, we report the detection of NIR lines from H-2 at 2.12 and 2.40 mu m in VLT/SINFONI spectra obtained between days 6489 and 10,120. The emission is concentrated to the core of the SN in contrast to Ha and approximately coincides with the [Si I]/[Fe II] emission detected previously in the ejecta. Different excitation mechanisms and power sources of the emission are discussed. From the nearly constant H-2 luminosities, we favor excitation resulting from the Ti-44 decay.

  • 16. Galper, A M
    et al.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zverev, V. G.
    et al.,
    Space gamma-observatory GAMMA-400 current status and perspectives2015In: FUNDAMENTAL RESEARCH IN PARTICLE PHYSICS AND COSMOPHYSICS, Elsevier, 2015, p. 177-182Conference paper (Refereed)
    Abstract [en]

    GAMMA-400 gamma-ray telescope is designed to measure fluxes of gamma-rays and the electron-positron cosmic ray component possibly generated in annihilation or decay of dark matter particles; to search for and study in detail discrete gamma-ray sources, to examine the energy spectra of Galactic and extragalactic diffuse gamma-rays, to study gamma-ray bursts and gamma-rays from the active Sun. GAMMA-400 consists of plastic scintillation anticoincidence top and lateral detectors, converter-tracker, plastic scintillation detectors for the time-of-flight system (TOF), two-part calorimeter (CC1 and CC2), plastic scintillation lateral detectors of calorimeter, plastic scintillation detectors of calorimeter, and neutron detector. The converter-tracker consists of 13 layers of double (x, y) silicon strip coordinate detectors (pitch of 0.08 mm). The first three and final one layers are without tungsten while the middle nine layers are interleaved with nine tungsten conversion foils. The thickness of CC1 and CC2 is 2 X-0 (0.1 lambda(0)) and 23 X-0 (1.1 lambda(0)) respectively (where X-0 is radiation length and lambda(0) is nuclear interaction one). The total calorimeter thickness is 25 X-0 or 1.2 lambda(0) for vertical incident particles registration and 54 X-0 or 2.5 lambda(0) for laterally incident ones. The energy range for gamma-rays and electrons (positrons) registration in the main aperture is from similar to 0.1 GeV to similar to 3.0 TeV. The gamma-ray telescope main aperture angular and energy resolutions are respectively similar to 0.01 degrees and similar to 1% for 10(2) GeV gamma-quanta, the proton rejection factor is similar to 5x10(5). The first three strip layers without tungsten provide the registration of gamma-rays down to similar to 20 MeV in the main aperture. Also this aperture allows investigating high energy light nuclei fluxes characteristics. Electrons, positrons, light nuclei and gamma-quanta will also register from the lateral directions due to special aperture configuration. Lateral aperture energy resolution is the same as for main aperture for electrons, positrons, light nuclei and gamma-quanta in energy range E>1.0 GeV. But using lateral aperture it is possible to detect low-energy gammas in the ranges 0.2 - 10 MeV and 10 MeV -1.0 GeV with energy resolution 8% - 2% and 2% correspondingly accordingly to GAMMA-400 "Technical Project" stage results. Angular resolution in the lateral aperture provides only for low-energy gamma-quanta from non-stationary events (GRB, solar flares and so on) due segments of CC2 count rate analysis. GAMMA-400 gamma-ray telescope will be installed onboard the Russian Space Observatory GAMMA-400. The lifetime of the space observatory will be at least seven years. The launch of the space observatory is scheduled for the early 2020s.

  • 17. Iyyani, S
    et al.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Axelsson, Magnus
    KTH, School of Engineering Sciences (SCI), Physics.
    Burgess, J. M.
    Guiriec, S.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lundman, Christoffer
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Moretti, Elena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    McGlynn, S.
    Nymark, Tanja
    KTH, School of Engineering Sciences (SCI), Physics.
    Rosquist, K.
    Variable jet properties in GRB 110721A: time resolved observations of the jet photosphere2013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 433, no 4, p. 2739-2748Article in journal (Refereed)
    Abstract [en]

    Fermi Gamma-ray Space Telescope observations of GRB 110721A have revealed two emission components from the relativistic jet: emission from the photosphere, peaking at similar to 100 keV, and a non-thermal component, which peaks at similar to 1000 keV. We use the photospheric component to calculate the properties of the relativistic outflow. We find a strong evolution in the flow properties: the Lorentz factor decreases with time during the bursts from G similar to 1000 to similar to 150 (assuming a redshift z = 2; the values are only weakly dependent on unknown efficiency parameters). Such a decrease is contrary to the expectations from the internal shocks and the isolated magnetar birth models. Moreover, the position of the flow nozzle measured from the central engine, r(0), increases by more than two orders of magnitude. Assuming a moderately magnetized outflow we estimate that r(0) varies from 10(6) to similar to 10(9) cm during the burst. We suggest that the maximal value reflects the size of the progenitor core. Finally, we show that these jet properties naturally explain the observed broken power-law decay of the temperature which has been reported as a characteristic for gamma-ray burst pulses.

  • 18.
    Iyyani, Shabnam
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ahlgren, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Burgess, J. Michael
    Larsson, Josefin
    Pe'er, A.
    Lundman, Christopher
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Axelsson, M.
    McGlynn, S.
    Extremely narrow spectrum of GRB110920A: further evidence for localized, subphotospheric dissipation2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 450, no 2, p. 1651-1663Article in journal (Refereed)
    Abstract [en]

    Much evidence points towards that the photosphere in the relativistic outflow in GRBs plays an important role in shaping the observed MeV spectrum. However, it is unclear whether the spectrum is fully produced by the photosphere or whether a substantial part of the spectrum is added by processes far above the photosphere. Here we make a detailed study of the. ray emission from single pulse GRB110920A which has a spectrum that becomes extremely narrow towards the end of the burst. We show that the emission can be interpreted as Comptonization of thermal photons by cold electrons in an unmagnetized outflow at an optical depth of tau similar to 20. The electrons receive their energy by a local dissipation occurring close to the saturation radius. The main spectral component of GRB110920A and its evolution is thus, in this interpretation, fully explained by the emission from the photosphere including localized dissipation at high optical depths.

  • 19.
    Larsson, Josefin
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    D'Ammando, F.
    Univ Bologna, Dipartimento Fis & Astron, Via Gobetti 93-2, I-40129 Bologna, Italy.;Ist Radio Astron Bologna, INAF, Via P Gobetti 101, I-40129 Bologna, Italy..
    Falocco, Serena
    KTH, School of Engineering Sciences (SCI), Physics.
    Giroletti, M.
    Ist Radio Astron Bologna, INAF, Via P Gobetti 101, I-40129 Bologna, Italy..
    Orienti, M.
    Ist Radio Astron Bologna, INAF, Via P Gobetti 101, I-40129 Bologna, Italy..
    Piconcelli, E.
    Osserv Astron Roma, INAF, Via Frascati 33, I-00040 Rome, Italy..
    Righini, S.
    Ist Radio Astron Bologna, INAF, Via P Gobetti 101, I-40129 Bologna, Italy..
    FBQS J1644+2619: multiwavelength properties and its place in the class of gamma-ray emitting Narrow Line Seyfert 1s2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 476, no 1, p. 43-55Article in journal (Refereed)
    Abstract [en]

    A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to be gamma-ray emitters. Understanding the properties of these sources is of interest since the majority of NLSy1s are very different from typical blazars. Here, we present a multifrequency analysis of FBQS J1644+2619, one of the most recently discovered gamma-ray emitting NLSy1s. We analyse an similar to 80 ks XMM-Newton observation obtained in 2017, as well as quasi-simultaneous multi-wavelength observations covering the radio-gamma-ray range. The spectral energy distribution of the source is similar to the other gamma-ray NLSy1s, confirming its blazar-like nature. The X-ray spectrum is characterized by a hard photon index (Gamma = 1.66) above 2 keV and a soft excess at lower energies. The hard photon index provides clear evidence that inverse Compton emission from the jet dominates the spectrum, while the soft excess can be explained by a contribution from the underlying Seyfert emission. This contribution can be fitted by reflection of emission from the base of the jet, as well as by Comptonization in a warm, optically thick corona. We discuss our results in the context of the other gamma-ray NLSy1s and note that the majority of them have similar X-ray spectra, with properties intermediate between blazars and radio-quiet NLSy1s.

  • 20.
    Larsson, Josefin
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Fransson, C.
    Spyromilio, J.
    Leibundgut, B.
    Challis, P.
    Chevalier, R. A.
    France, K.
    Jerkstrand, A.
    Kirshner, R. P.
    Lundqvist, P.
    Matsuura, M.
    McCray, R.
    Smith, N.
    Sollerman, J.
    Garnavich, P.
    Heng, K.
    Lawrence, S.
    Mattila, S.
    Migotto, K.
    Sonneborn, G.
    Taddia, F.
    Wheeler, J. C.
    THREE-DIMENSIONAL DISTRIBUTION OF EJECTA IN SUPERNOVA 1987A AT 10,000 DAYS2016In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 833, no 2, article id 147Article in journal (Refereed)
    Abstract [en]

    Due to its proximity, SN. 1987A offers a unique opportunity to directly observe the geometry of a stellar explosion as it unfolds. Here we present spectral and imaging observations of SN. 1987A obtained similar to 10,000 days after the explosion with HST/STIS and VLT/SINFONI at optical and near-infrared wavelengths. These observations allow us to produce the most detailed 3D map of Ha to date, the first 3D maps for [Ca II] lambda lambda 7292, 7324, [O I] lambda lambda 6300, 6364, and Mg. II lambda lambda 9218, 9244, as well as new maps for [Si I]+[Fe II] 1.644 mu m and He I 2.058 mu m. A comparison with previous observations shows that the [Si I]+[Fe II] flux and morphology have not changed significantly during the past ten years, providing evidence that this line is powered by Ti-44. The time evolution of Ha shows that it is predominantly powered by X-rays from the ring, in agreement with previous findings. All lines that have sufficient signal show a similar large-scale 3D structure, with a north-south asymmetry that resembles a broken dipole. This structure correlates with early observations of asymmetries, showing that there is a global asymmetry that extends from the inner core to the outer envelope. On smaller scales, the two brightest lines, Ha and [Si I]+[Fe II] 1.644 mu m, show substructures at the level of similar to 200-1000 km s(-1) and clear differences in their 3D geometries. We discuss these results in the context of explosion models and the properties of dust in the ejecta.

  • 21.
    Larsson, Josefin
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Fransson, Claes
    Kjaer, Karina
    Jerkstrand, Anders
    Kirshner, Robert P.
    Leibundgut, Bruno
    Lundqvist, Peter
    Mattila, Seppo
    McCray, Richard
    Sollerman, Jesper
    Spyromilio, Jason
    Wheeler, J. Craig
    The morphology of the ejecta in supernova 1987a: A study over time and wavelength2013In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 768, no 1, p. 89-Article in journal (Refereed)
    Abstract [en]

    We present a study of the morphology of the ejecta in Supernova 1987A based on images and spectra from the Hubble Space Telescope (HST) as well as integral field spectroscopy from VLT/SINFONI. The HST observations were obtained between 1994 and 2011 and primarily probe the outer H-rich zones of the ejecta. The SINFONI observations were obtained in 2005 and 2011 and instead probe the [Si I]+[Fe II] emission from the inner regions. We find a strong temporal evolution of the morphology in the HST images, from a roughly elliptical shape before similar to 5000 days, to a more irregular, edge-brightened morphology with a "hole" in the middle thereafter. This transition is a natural consequence of the change in the dominant energy source powering the ejecta, from radioactive decay before similar to 5000 days to X-ray input from the circumstellar interaction thereafter. The [Si I]+[Fe II] images display a more uniform morphology, which may be due to a remaining significant contribution from radioactivity in the inner ejecta and the higher abundance of these elements in the core. Both the Ha and the [Si I]+[Fe II] line profiles show that the ejecta are distributed fairly close to the plane of the inner circumstellar ring, which is assumed to define the rotational axis of the progenitor star. The Ha emission extends to higher velocities than [Si I]+[Fe II], as expected from theoretical models. There is no clear symmetry axis for all the emission. Instead, we find that the emission is concentrated to clumps and that the emission is distributed somewhat closer to the ring in the north than in the south. This north-south asymmetry may be partially explained by dust absorption. We compare our results with explosion models and find some qualitative agreement, but note that the observations show a higher degree of large-scale asymmetry.

  • 22.
    Larsson, Josefin
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Racusin, J. L.
    Burgess, J. Michael
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Evidence for jet launching close to the black hole in GRB 101219b: A Fermi grb dominated by thermal emission2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 800, no 2, article id L34Article in journal (Refereed)
    Abstract [en]

    We present observations by the Fermi Gamma-Ray Space Telescope Gamma-Ray Burst Monitor (GBM) of the nearby (z = 0.55) GRB 101219B. This burst is a long GRB, with an associated supernova and with a blackbody (BB) component detected in the early afterglow observed by the Swift X-ray Telescope (XRT). Here we show that the prompt gamma-ray emission has a BB spectrum, making this the second such burst observed by Fermi GBM. The properties of the BB, together with the redshift and our estimate of the radiative efficiency makes it possible to calculate the absolute values of the properties of the outflow. We obtain an initial Lorentz factor G = 138 +/- 8, a photospheric radius r(phot) = 4.4 +/- 1.9 x 10(11) cm, and a launch radius r(0) = 2.7 +/- 1.6 x 10(7) cm. The latter value is close to the black hole and suggests that the jet has a relatively unobstructed path through the star. There is no smooth connection between the BB components seen by GBM and XRT, ruling out the scenario that the late emission is due to high-latitude effects. In the interpretation that the XRT BB is prompt emission due to late central engine activity, the jet either has to be very wide or have a clumpy structure where the emission originates from a small patch. Other explanations for this component, such as emission from a cocoon surrounding the jet, are also possible.

  • 23. Leonov, A. A.
    et al.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zverev, V. G.
    et al.,
    Separation of electrons and protons in the GAMMA-400 gamma-ray telescope2015In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 56, no 7, p. 1538-1545Article in journal (Refereed)
    Abstract [en]

    The GAMMA-400 telescope will measure the fluxes of gamma rays and cosmic-ray electrons and positrons in the energy range from 100 MeV to several TeV. These measurements will allow it to achieve the following scientific objectives: search for signatures of dark matter, investigation of gamma-ray point-like and extended sources, study of the energy spectrum of the Galactic and extragalactic diffuse emission, study of gamma-ray bursts and gamma-ray emission from the active Sun, together with high-precision measurements of the high-energy electrons and positrons spectra, protons and nuclei up to the knee. The bulk of cosmic rays are protons and helium nuclei, whereas the lepton component in the total flux is similar to 10(-3) at high energy. In the present paper, the simulated capability of the GAMMA-400 telescope to distinguish electrons and positrons from protons in cosmic rays is addressed. The individual contribution to the proton rejection from each detector system of GAMMA-400 is studied separately. The use of the combined information from all detectors allows us to reach a proton rejection of the order of similar to 4 x 10(5) for vertical incident particles and similar to 3 x 10(5) for particles with initial inclination of 30 degrees in the electron energy range from 50 GeV to 1 TeV. (C) 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.

  • 24.
    Nandi, Sumana
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jamrozy, M.
    Roy, R.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Saikia, D. J.
    Baes, M.
    Singh, M.
    Tale of J1328+2752: a misaligned double-double radio galaxy hosted by a binary black hole?2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 467, no 1, p. L56-L60Article in journal (Refereed)
    Abstract [en]

    We present a radio and optical study of the double-double radio galaxy J1328+2752 based on new low-frequency Giant Metrewave Radio Telescope observations and Sloan Digital Sky Survey (SDSS) data. The radio data were used to investigate the morphology and to perform a spectral index analysis. In this source, we find that the inner double is misaligned by similar to 30 degrees from the axis of the outer diffuse structure. The SDSS spectrum shows that the central component has double-peaked line profiles with different emission strengths. The average velocity offset of the two components is 235 +/- 10.5 kms(-1). The misaligned radio morphology along with the double-peaked emission lines indicate that this source is a potential candidate binary supermassive black hole. This study further supports mergers as a possible explanation for repeated jet activity in radio sources.

  • 25. Pe'er, Asaf
    et al.
    Barlow, Hugh
    O'Mahony, Shane
    Margutti, Raffaella
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oskar Klein Ctr Cosmoparticle Phys, Sweden.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oskar Klein Ctr Cosmoparticle Phys, Sweden.
    Lazzati, Davide
    Livio, Mario
    HYDRODYNAMIC PROPERTIES of GAMMA-RAY BURST OUTFLOWS DEDUCED from the THERMAL COMPONENT2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 813, no 2, article id 127Article in journal (Refereed)
    Abstract [en]

    We study the properties of a significant thermal emission component that was identified in 47 gamma-ray bursts observed by different instruments. Within the framework of the "fireball" model, we deduce the values of the Lorentz factor Gamma, and the acceleration radius, r(0), for these bursts. We find that all the values of Gamma in our sample are in the range 10(2) <= Gamma <= 10(3), with <Gamma > = 370. We find a very weak dependence of Gamma on the acceleration radius r0, Gamma proportional to r(0)(alpha) with alpha - -0.10 +/- 0.09 at the sigma - 2.1 confidence level. The values of r(0) span a wide range, 10(6.5) <= r(0) <= 10(9.5) cm, with a mean value of < r(0)> similar to 10(8) cm. This is higher than the gravitational radius of a 10 M-circle dot black hole by a factor of approximate to 30. We argue that this result provides indirect evidence for jet propagation inside a massive star, and suggests the existence of recollimation shocks that take place close to this radius.

  • 26. Preece, R.
    et al.
    Burgess, J. Michael
    University of Alabama in Huntsville, United States.
    von Kienlin, A.
    Bhat, P. N.
    Briggs, M. S.
    Byrne, D.
    Chaplin, V.
    Cleveland, W.
    Collazzi, A. C.
    Connaughton, V.
    Diekmann, A.
    Fitzpatrick, G.
    Foley, S.
    Gibby, M.
    Giles, M.
    Goldstein, A.
    Greiner, J.
    Gruber, D.
    Jenke, P.
    Kippen, R. M.
    Kouveliotou, C.
    McBreen, S.
    Meegan, C.
    Paciesas, W. S.
    Pelassa, V.
    Tierney, D.
    van der Horst, A. J.
    Wilson-Hodge, C.
    Xiong, S.
    Younes, G.
    Yu, H. -F
    Ackermann, M.
    Ajello, M.
    Axelsson, Magnus
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Baldini, L.
    Barbiellini, G.
    Baring, M. G.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Bonamente, E.
    Bregeon, J.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Cominsky, L. R.
    Conrad, J.
    D'Ammando, F.
    de Angelis, A.
    de Palma, F.
    Dermer, C. D.
    Desiante, R.
    Digel, S. W.
    Di Venere, L.
    Drell, P. S.
    Drlica-Wagner, A.
    Favuzzi, C.
    Franckowiak, A.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gehrels, N.
    Germani, S.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Godfrey, G.
    Granot, J.
    Grenier, I. A.
    Guiriec, S.
    Hadasch, D.
    Hanabata, Y.
    Harding, A. K.
    Hayashida, M.
    Iyyani, S.
    Jogler, T.
    Joannesson, G.
    Kawano, T.
    Knoedlseder, J.
    Kocevski, D.
    Kuss, M.
    Lande, J.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Larsson, S.
    Latronico, L.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Mayer, M.
    Mazziotta, M. N.
    Michelson, P. F.
    Mizuno, T.
    Monzani, M. E.
    Moretti, Elena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Morselli, A.
    Murgia, S.
    Nemmen, R.
    Nuss, E.
    Nymark, Tanja
    KTH, School of Engineering Sciences (SCI), Physics.
    Ohno, M.
    Ohsugi, T.
    Okumura, A.
    Omodei, N.
    Orienti, M.
    Paneque, D.
    Perkins, J. S.
    Pesce-Rollins, M.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Racusin, J. L.
    Raino, S.
    Rando, R.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Ritz, S.
    Roth, M.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sartori, A.
    Scargle, J. D.
    Schulz, A.
    Sgro, C.
    Siskind, E. J.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Tajima, H.
    Takahashi, H.
    Thayer, J. G.
    Thayer, J. B.
    Tibaldo, L.
    Tinivella, M.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Vianello, G.
    Vitale, V.
    Werner, M.
    Winer, B. L.
    Wood, K. S.
    Zhu, S.
    The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks2014In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 343, no 6166, p. 51-54Article in journal (Refereed)
    Abstract [en]

    Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 seconds is possibly the brightest well-isolated pulse observed to date. A fine time resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. However, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. It is difficult for any of the existing models to account for all of the observed spectral and temporal behaviors simultaneously.

  • 27. Soffitta, Paolo
    et al.
    Barcons, Xavier
    Bellazzini, Ronaldo
    Braga, Joao
    Costa, Enrico
    Fraser, George W.
    Gburek, Szymon
    Huovelin, Juhani
    Matt, Giorgio
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Poutanen, Juri
    Reglero, Victor
    Santangelo, Andrea
    Sunyaev, Rashid A.
    Tagliaferri, Gianpiero
    Weisskopf, Martin
    Aloisio, Roberto
    Amato, Elena
    Attina, Primo
    Axelsson, Magnus
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    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, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kaaret, Philip
    Karas, Vladimir
    Kuss, Michael
    Lai, Dong
    La Rosa, Giovanni
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Larsson, Stefan
    Latronico, Luca
    Maggio, Antonio
    Maia, Jorge
    Marin, Frederic
    Massai, Marco Maria
    Mineo, Teresa
    Minuti, Massimo
    Moretti, Elena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    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, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    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 explorer2013In: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 36, no 3, p. 523-567Article in journal (Refereed)
    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.

  • 28. Sofitta, P
    et al.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Axelsson, M.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Chauvin, Maxime
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Burgess, Michael
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kiss, Moszi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Xie, F
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zoghbi, A.
    et al.,
    XIPE the X-ray Imaging Polarimetry Explorer2016In: Proceedings of SPIE, SPIE - International Society for Optical Engineering, 2016, Vol. 9905, article id UNSP 990515Conference paper (Refereed)
    Abstract [en]

    XIPE, the X-ray Imaging Polarimetry Explorer, is a mission dedicated to X-ray Astronomy. At the time of writing XIPE is in a competitive phase A as fourth medium size mission of ESA (M4). It promises to reopen the polarimetry window in high energy Astrophysics after more than 4 decades thanks to a detector that efficiently exploits the photoelectric effect and to X-ray optics with large effective area. XIPE uniqueness is time-spectrally-spatially- resolved X-ray polarimetry as a breakthrough in high energy astrophysics and fundamental physics. Indeed the payload consists of three Gas Pixel Detectors at the focus of three X-ray optics with a total effective area larger than one XMM mirror but with a low weight. The payload is compatible with the fairing of the Vega launcher. XIPE is designed as an observatory for X- ray astronomers with 75% of the time dedicated to a Guest Observer competitive program and it is organized as a consortium across Europe with main contributions from Italy, Germany, Spain, United Kingdom, Poland, Sweden.

  • 29. 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, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    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, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Popov, A. V.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    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, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Kheymits, M. D.
    Yurkin, Y. T.
    The GAMMA-400 experiment: Status and prospects2015In: Bulletin of the Russian Academy of Sciences: Physics, ISSN 1062-8738, Vol. 79, no 3, p. 417-420Article in journal (Refereed)
    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.

  • 30. Topchiev, N. P.
    et al.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden.
    Zverev, V. G.
    et al.,
    The GAMMA-400 gamma-ray telescope for precision gamma-ray emission investigations2016In: INTERNATIONAL CONFERENCE ON PARTICLE PHYSICS AND ASTROPHYSICS (ICPPA-2015), PTS 1-4, Institute of Physics (IOP), 2016Conference paper (Refereed)
    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.

  • 31.
    Valan, Vlasta
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ahlgren, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Thermal components in the early X-ray afterglows of GRBs: likely cocoon emission and constraints on the progenitorsManuscript (preprint) (Other academic)
  • 32.
    Valan, Vlasta
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ahlgren, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Thermal components in the early X-ray afterglows of GRBs: likely cocoon emission and constraints on the progenitorsManuscript (preprint) (Other academic)
  • 33.
    Valan, Vlasta
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre, AlbaNova, SE-106-91 Stockholm, Sweden.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre, AlbaNova, SE-106-91 Stockholm, Sweden.
    Ahlgren, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre, AlbaNova, SE-106-91 Stockholm, Sweden.
    Thermal components in the early X-ray afterglows of GRBs: likely cocoon emission and constraints on the progenitors2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 474, no 2, p. 2401-2418Article in journal (Refereed)
    Abstract [en]

    The early X-ray afterglows of gamma-ray bursts (GRBs) are usually well described by absorbed power laws. However, in some cases, additional thermal components have been identified. The origin of this emission is debated, with proposed explanations including supernova shock breakout, emission from a cocoon surrounding the jet, as well as emission from the jet itself. A larger sample of detections is needed in order to place constraints on these different models. Here, we present a time-resolved spectral analysis of 74 GRBs observed by Swift X-ray Telescope in a search for thermal components. We report six detections in our sample, and also confirm an additional three cases that were previously reported in the literature. The majority of these bursts have a narrow range of blackbody radii around similar to 2 x 10(12) cm, despite having a large range of luminosities (L-peak similar to 10(47)-10(51) erg s(-1)). This points to an origin connected to the progenitor stars, and we suggest that emission from a cocoon breaking out from a thick wind may explain the observations. For two of the bursts in the sample, an explanation in terms of late prompt emission from the jet is instead more likely. We also find that these thermal components are preferentially detected when the X-ray luminosity is low, which suggests that they may be hidden by bright afterglows in the majority of GRBs.

1 - 33 of 33
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