High Energy Spectral Evolution of V404 Cygni during the 2015 June Outburst as Observed by INTEGRAL
Date Issued
2015
Author(s)
•
•
•
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Roques, Jean-Pierre
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Jourdain, Elisabeth
Description
The Italian authors acknowledge ASI/INAF agreement No. 2013-025-R.0 and thank M. Federici for the setup and maintenance of the INTEGRAL archive and analysis S/W at IAPS. The INTEGRAL /SPI project has been completed under the responsibility and leadership of CNES. We are grateful to ASI, CEA, CNES, DLR, ESA, INTA, NASA, and OSTC for support. We also thank the anonymous referee for precious suggestions.
Abstract
The black hole binary GS 2023+338 exhibited an unprecedently bright outburst in 2015 June. On 2015 June 17, the high energy instruments on board INTEGRAL detected an extremely variable emission during both bright and low luminosity phases, with dramatic variations of the hardness ratio on timescales of approximately seconds. The analysis of the IBIS and SPI data reveals the presence of hard spectra in the brightest phases, compatible with thermal Comptonization with a temperature of kTe ̃ 40 keV. The seed photon’s temperature is best fit by kT0 ̃ 7 keV, which is too high to be compatible with blackbody emission from the disk. This result is consistent with the seed photons being provided by a different source, which we hypothesize to be a synchrotron driven component in the jet. During the brightest phase of flares, the hardness shows a complex pattern of correlation with flux, with the maximum energy released in the range of 40-100 keV. The hard-X-ray variability for E > 50 keV is correlated with flux variations in the softer band, showing that the overall source variability cannot originate entirely from absorption, but at least part of it is due to the central accreting source. INTEGRAL is an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA.
Volume
813
Issue
1
Start page
L21
Issn Identifier
2041-8205
Ads BibCode
2015ApJ...813L..21N
Rights
open.access
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