Published January 1, 2014
| Version v1
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Multiwavelength observations of the black hole transient Swift J1745-26 during the outburst decay
Creators
- 1. Sabanci Univ, Fac Engn & Nat Sci, TR-34956 Istanbul, Turkey
- 2. Middle E Tech Univ, Dept Phys, TR-06530 Ankara, Turkey
- 3. Istanbul Univ, Astron & Space Sci Dept, TR-34119 Istanbul, Turkey
- 4. Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
- 5. Univ Erlangen Nurnberg, Dr Karl Remeis Sternwarte & Erlangen Ctr Astropar, D-96049 Bamberg, Germany
- 6. European Space Agcy, European Space Astron Ctr, E-28691 Madrid, Spain
- 7. ISSI, CH-3012 Bern, Switzerland
- 8. Univ Southampton, Sch Phys & Astron, Fac Phys Sci & Engn, Southampton SO17 1BJ, Hants, England
- 9. INAF Osservatorio Astron Brera, I-23807 Merate, Italy
- 10. Univ Cape Town, Dept Astron, ZA-7701 Rondebosch, South Africa
- 11. Univ Oxford, Dept Phys, Oxford OX1 3RH, England
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 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.
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