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  • 1.
    Heckmann, Lea
    et al.
    Tech Univ Wien, Fac Phys, Vienna, Austria.;Max Planck Inst Phys & Astrophys, Munich, Germany..
    Iyer, Nirmal
    KTH, Skolan för teknikvetenskap (SCI), Fysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden..
    Kiss, Mózsi
    KTH, Skolan för teknikvetenskap (SCI), Fysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden..
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden..
    Xie, Fei
    KTH, Skolan för teknikvetenskap (SCI), Fysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, Stockholm, Sweden.;Osservatorio Astron Cagliari, INAF, Selargius, Italy..
    Gamma-ray burst localization strategies for the SPHiNX hard x-ray polarimeter2019Inngår i: JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS, ISSN 2329-4124, Vol. 5, nr 1, artikkel-id 018002Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    SPHiNX is a proposed gamma-ray burst (GRB) polarimeter mission operating in the energy range 50 to 600 keV with the aim of studying the prompt emission phase. The polarization sensitivity of SPHiNX reduces as the uncertainty on the GRB sky position increases. The stand-alone ability of the SPHiNX design to localize GRB positions is explored via Geant4 simulations. Localization at the level of a few degrees is possible using three different routines. This results in a large fraction (>80%) of observed GRBs having a negligible (<5%) reduction in polarization sensitivity due to the uncertainty in localization. 

  • 2.
    Kushwah, Rakhee
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Iyer, Nirmal
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Kiss, Mózsi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Stana, Theodor-Adrian
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    A Compton polarimeter using scintillators read out with MPPCs through Citiroc ASIC2019Inngår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 943, artikkel-id 162376Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In recent years, a number of purpose-built scintillator-based polarimeters have studied bright astronomical sources for the first time in the hard X-ray band (tens to hundreds of keV). The addition of polarimetry can help data interpretation by resolving model-dependent degeneracies. The typical instrument approach is that incident X-rays scatter off a plastic scintillator into an adjacent scintillator cell. In all missions to date, the scintillators are read out using traditional vacuum tube photo-multipliers (PMTs). The advent of solid-state PMTs (“silicon PM” or “MPPC”) is attractive for space-based instruments since the devices are compact, robust and require a low bias voltage. We have characterised the plastic scintillator, EJ-248M, optically coupled to a multi-pixel photon counter (MPPC) and read out with the Citiroc ASIC. A light-yield of 1.6 photoelectrons/keV has been obtained, with a low energy detection threshold of ≲5 keV at room temperature. We have also constructed an MPPC-based polarimeter-demonstrator in order to investigate the feasibility of such an approach for future instruments. Incident X-rays scatter from a plastic-scintillator bar to surrounding cerium-doped GAGG (Gadolinium Aluminium Gallium Garnet) scintillators yielding time-coincident signals in the scintillators. We have determined the polarimetric response of this set-up using both unpolarised and polarised ∼50 keV X-rays. We observe a clear asymmetry in the GAGG counting rates for the polarised beam. The low-energy detection threshold in the plastic scintillator can be further reduced using a coincidence technique. The demonstrated polarimeter design shows promise as a space-based Compton polarimeter and we discuss ways in which our polarimeter can be adapted for such a mission.

  • 3. Nandi, A.
    et al.
    Mandal, S.
    Sreehari, H.
    Radhika, D.
    Das, S.
    Chattopadhyay, I.
    Iyer, Nirmal
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Agrawal, V. K.
    Aktar, R.
    Accretion flow dynamics during 1999 outburst of XTE J1859+226—modeling of broadband spectra and constraining the source mass2018Inngår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 363, nr 5, artikkel-id 90Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine the dynamical behavior of accretion flow around XTE J1859+226 during the 1999 outburst by analyzing the entire outburst data (∼166 days) from RXTE Satellite. Towards this, we study the hysteresis behavior in the hardness intensity diagram (HID) based on the broadband (3–150 keV) spectral modeling, spectral signature of jet ejection and the evolution of Quasi-periodic Oscillation (QPO) frequencies using the two-component advective flow model around a black hole. We compute the flow parameters, namely Keplerian accretion rate (m˙ d), sub-Keplerian accretion rate (m˙ h), shock location (rs) and black hole mass (Mbh) from the spectral modeling and study their evolution along the q-diagram. Subsequently, the kinetic jet power is computed as Ljetobs∼3–6×1037ergs−1 during one of the observed radio flares which indicates that jet power corresponds to 8–16% mass outflow rate from the disc. This estimate of mass outflow rate is in close agreement with the change in total accretion rate (∼14%) required for spectral modeling before and during the flare. Finally, we provide a mass estimate of the source XTE J1859+226 based on the spectral modeling that lies in the range of 5.2–7.9 M⊙ with 90% confidence.

  • 4.
    Pearce, Mark
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Eliasson, Linda
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Iyer, Nirmal
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Kiss, Mózsi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Kushwah, Rakhee
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Larsson, Josefin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Lundman, Christoffer
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Mikhalev, Victor
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Stana, Theodor-Adrian
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Takahashi, H.
    Hiroshima Univ, Dept Phys Sci, Hiroshima 7398526, Japan..
    Xie, Fei
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Science prospects for SPHiNX - A small satellite GRB polarimetry mission2019Inngår i: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 104, s. 54-63Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Gamma-ray bursts (GRBs) are exceptionally bright electromagnetic events occurring daily on the sky. The prompt emission is dominated by X-/gamma-rays. Since their discovery over 50 years ago, GRBs are primarily studied through spectral and temporal measurements. The properties of the emission jets and underlying processes are not well understood. A promising way forward is the development of missions capable of characterising the linear polarisation of the high-energy emission. For this reason, the SPHiNX mission has been developed for a small-satellite platform. The polarisation properties of incident high-energy radiation (50-600 keV) are determined by reconstructing Compton scattering interactions in a segmented array of plastic and Gd3Al2Ga3O12(Ce) (GAGG(Ce)) scintillators. During a two-year mission, similar to 200 GRBs will be observed, with similar to 50 yielding measurements where the polarisation fraction is determined with a relative error <= 10%. This is a significant improvement compared to contemporary missions. This performance, combined with the ability to reconstruct GRB localisation and spectral properties, will allow discrimination between leading classes of emission models.

  • 5.
    Radhika, D.
    et al.
    Dayananda Sagar Univ, Dept Phys, Bangalore 560068, Karnataka, India..
    Sreehari, H.
    ISRO Satellite Ctr, Space Astron Grp, SSIF ISITE Campus,Outer Ring Rd, Bangalore 560037, Karnataka, India.;Indian Inst Sci, Bangalore 560012, Karnataka, India..
    Nandi, A.
    ISRO Satellite Ctr, Space Astron Grp, SSIF ISITE Campus,Outer Ring Rd, Bangalore 560037, Karnataka, India..
    Iyer, Nirmal
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Albanova Univ Ctr, KTH PAP, S-10691 Stockholm, Sweden..
    Mandal, S.
    Indian Inst Space Sci & Technol, Thiruvananthapuram, Kerala, India..
    Broad-band spectral evolution and temporal variability of IGR J17091-3624 during its 2016 outburst: SWIFT and NuSTAR results2018Inngår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 363, nr 9, artikkel-id 189Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the 2016 outburst of the transient Galactic Black Hole candidate IGR J17091-3624 based on the observation campaign carried out with SWIFT and NuSTAR. The outburst profile, as observed with SWIFT-XRT, shows a typical 'q'-shape in the Hardness Intensity Diagram (HID). Based on the spectral and temporal evolution of the different parameters, we are able to identify all the spectral states in the q-profile of HID and the Hardness-RMS diagram (HRD). Both XRT and NuSTAR observations show an evolution of low frequency Quasi periodic oscillations (QPOs) during the low hard and hard intermediate states of the outburst rising phase. We also find mHz QPOs along-with distinct coherent class variabilities (heartbeat oscillations) with different timescales, similar to the -class (observed in GRS 1915+105). Phenomenological modelling of the broad-band XRT and NuSTAR spectra also reveals the evolution of high energy cut-off and presence of reflection from ionized material during the rising phase of the outburst. Further, we conduct the modelling of X-ray spectra of SWIFT and NuSTAR in 0.5-79 keV to understand the accretion flow dynamics based on two component flow model. From this modelling, we constrain the mass of the source to be in the range of with 90% confidence, which is consistent with earlier findings.

  • 6.
    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). 

  • 7. 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.

  • 8.
    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.

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