Multiwavelength observations of the black hole transient Swift J1745-26 during the outburst decay

Kalemci, E.; Arabacı, M. Özbey; Güver, T.; Russell, D. M.; Tomsick, J. A.; Wilms, J.; Weidenspointner, G.; Kuulkers, E.; Falanga, M.; Dinçer, T.; Drave, S.; Belloni, T.; Coriat, M.; Lewis, F.; Muñoz-Darias, T.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 445, Issue 2, p.1288-1298

Advertised on:
12
2014
Number of authors
15
IAC number of authors
1
Citations
13
Refereed citations
12
Description
We characterized the broad-band X-ray spectra of Swift J1745-26 during the decay of the 2013 outburst using INTEGRAL ISGRI, JEM-X and Swift XRT. The X-ray evolution is compared to the evolution in optical and radio. We fit the X-ray spectra with phenomenological and Comptonization models. We discuss possible scenarios for the physical origin of an ˜50 d flare observed both in optical and X-rays ˜170 d after the peak of the outburst. We conclude that it is a result of enhanced mass accretion in response to an earlier heating event. We characterized the evolution in the hard-X-ray band and showed that for the joint ISGRI-XRT fits, the e-folding energy decreased from 350 to 130 keV, while the energy where the exponential cut-off starts increased from 75 to 112 keV as the decay progressed. We investigated the claim that high-energy cut-offs disappear with the compact jet turning on during outburst decays, and showed that spectra taken with HEXTE on RXTE provide insufficient quality to characterize cut-offs during the decay for typical hard-X-ray fluxes. Long INTEGRAL monitoring observations are required to understand the relation between the compact jet formation and hard-X-ray behaviour. We found that for the entire decay (including the flare), the X-ray spectra are consistent with thermal Comptonization, but a jet synchrotron origin cannot be ruled out.
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