Multiwavelength observations of the black hole transient Swift J1745-26 during the outburst decay
Kalemci, Emrah and Arabacı, Mehtap Ö. and Güver, Tolga and Russell, David M. and Tomsick, John A. and Wilms, Joern and Weidenspointtner, Georg and Kuulkers, Erik and Falanga, Maurizio and Dinçer, Tolga and Drave, Sebastian and Belloni, Tomaso and Coriat, Mickael and Lewis, Fraser and Munoz-Darias, Teo (2014) Multiwavelength observations of the black hole transient Swift J1745-26 during the outburst decay. Monthly Notices of the Royal Astronomical Society, 445 (2). pp. 1288-1298. ISSN 0035-8711 (Print) 1365-2966 (Online)
Official URL: http://dx.doi.org/10.1093/mnras/stu1851
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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