Emrah Kalemci (Sabanci, Turkey), Mehtap Ozbey Arabaci (Ankara, Turkey), Tolga Guver (Istanbul, Turkey), David M. Russell (New York Abu Dhabi), John Tomsick (Berkeley), Joern Wilms (Erlangen-Nurnberg), Georg Weidenspointner (Hamburg, MPI Garching), Erik Kuulkers (ESAC Madrid), Maurizio Falanga (Bern), Tolga Dincer (Sabanci, Turkey), Sebastian Drave (Southampton), Tomaso Belloni (Brera), Mickael Coriat (Cape Town), Fraser Lewis (FT), Teo Munoz-Darias (Oxford)

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 a ~50 day flare observed both in optical and X- rays ~170 days 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 keV to 130 keV, while the energy where the exponential cut-off starts increased from 75 keV 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 behavior. 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.

Paper here