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Iyer, Nirmal
Publications (4 of 4) Show all publications
Sreehari, H., Iyer, N., Radhika, D., Nandi, A. & Mandal, S. (2019). Constraining the mass of the black hole GX 339-4 using spectro-temporal analysis of multiple outbursts. Advances in Space Research, 63(3), 1374-1386
Open this publication in new window or tab >>Constraining the mass of the black hole GX 339-4 using spectro-temporal analysis of multiple outbursts
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2019 (English)In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 63, no 3, p. 1374-1386Article in journal (Refereed) Published
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). 

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2019
Keywords
Black hole candidate, Accretion discs, X ray outbursts
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-244527 (URN)10.1016/j.asr.2018.10.042 (DOI)000457951400020 ()2-s2.0-85056391444 (Scopus ID)
Note

QC 20190403

Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2019-04-04Bibliographically approved
Heckmann, L., Iyer, N., Kiss, M., Pearce, M. & Xie, F. (2019). Gamma-ray burst localization strategies for the SPHiNX hard x-ray polarimeter. JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS, 5(1), Article ID 018002.
Open this publication in new window or tab >>Gamma-ray burst localization strategies for the SPHiNX hard x-ray polarimeter
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2019 (English)In: JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS, ISSN 2329-4124, Vol. 5, no 1, article id 018002Article in journal (Refereed) Published
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. 

Place, publisher, year, edition, pages
SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2019
Keywords
polarimeters, x-rays, gamma ray bursts, Monte-Carlo simulations, analysis techniques
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-249826 (URN)10.1117/1.JATIS.5.1.018002 (DOI)000463885600012 ()2-s2.0-85062620103 (Scopus ID)
Note

QC 20190423

Available from: 2019-04-23 Created: 2019-04-23 Last updated: 2019-05-16Bibliographically approved
Pearce, M., Eliasson, L., Iyer, N., Kiss, M., Kushwah, R., Larsson, J., . . . Xie, F. (2019). Science prospects for SPHiNX - A small satellite GRB polarimetry mission. Astroparticle physics, 104, 54-63
Open this publication in new window or tab >>Science prospects for SPHiNX - A small satellite GRB polarimetry mission
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2019 (English)In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 104, p. 54-63Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Polarimetry, X-ray, Gamma-ray burst, Small satellite
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-238104 (URN)10.1016/j.astropartphys.2018.08.007 (DOI)000447479300004 ()2-s2.0-85052499332 (Scopus ID)
Note

QC 20190111

Available from: 2019-01-11 Created: 2019-01-11 Last updated: 2019-01-11Bibliographically approved
Radhika, D., Sreehari, H., Nandi, A., Iyer, N. & Mandal, S. (2018). Broad-band spectral evolution and temporal variability of IGR J17091-3624 during its 2016 outburst: SWIFT and NuSTAR results. Astrophysics and Space Science, 363(9), Article ID 189.
Open this publication in new window or tab >>Broad-band spectral evolution and temporal variability of IGR J17091-3624 during its 2016 outburst: SWIFT and NuSTAR results
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2018 (English)In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 363, no 9, article id 189Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Accretion, accretion disks, Black hole physics, X-rays: binaries, ISM: jets and outflows, Stars: individual: IGR J17091-3624
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-234580 (URN)10.1007/s10509-018-3411-1 (DOI)000442478500001 ()2-s2.0-85052240883 (Scopus ID)
Note

QC 20180917

Available from: 2018-09-17 Created: 2018-09-17 Last updated: 2018-09-17Bibliographically approved
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