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Title: HIGH ENERGY SPECTRAL EVOLUTION OF V404 CYGNI DURING THE 2015 JUNE OUTBURST AS OBSERVED BY INTEGRAL

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 kT{sub e} ∼ 40 keV. The seed photon’s temperature is best fit by kT{sub 0} ∼ 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.
Authors:
; ; ;  [1] ; ;  [2]
  1. Istituto di Astrofisica e Planetologia Spaziali, INAF, Via Fosso del Cavaliere 100, I-00133 Roma (Italy)
  2. Université de Toulouse, UPS-OMP CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, F-31028 Toulouse cedex 4 (France)
Publication Date:
OSTI Identifier:
22518711
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 813; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BINARY STARS; BLACK HOLES; CORRELATIONS; GAMMA RADIATION; HARD X RADIATION; HARDNESS; JETS; KEV RANGE; LUMINOSITY; STAR ACCRETION; VARIATIONS