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

Kalemci E., Arabaci M. O., Guver T., Russell D. M., Tomsick J. A., Wilms J., ...More

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, vol.445, no.2, pp.1288-1298, 2014 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 445 Issue: 2
  • Publication Date: 2014
  • Doi Number: 10.1093/mnras/stu1851
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.1288-1298
  • Keywords: stars: black holes, stars: individual: Swift J174510.8-2624, X-rays: binaries, X-RAY-EMISSION, BROAD-BAND SPECTRUM, CANDIDATE XTE J1550-564, COMPACT JET, GX 339-4, SYNCHROTRON EMISSION, STATE TRANSITIONS, RADIO-EMISSION, CYGNUS X-1, ACCRETION
  • Istanbul University Affiliated: Yes


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 similar to 50 d flare observed both in optical and X-rays similar to 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.