Repeated Short-term Spectral Softening in the Low/Hard State of the Galactic Black-Hole Candidate Swift J1753.5-0127

Abstract

We report MAXI and Swift observations of short-term spectral softenings of the galactic black-hole X-ray binary Swift J1753.5-0127 in the low/hard state. These softening events are characterized by a simultaneous increase of soft X-rays (2-4 keV) and a decrease of hard X-rays (15-50 keV) lasting for a few tens of days. The X-ray energy spectra during the softening periods can be reproduced with a model consisting of a multi-color disk blackbody and its Comptonized component. The fraction of the Comptonized component decreased from 0.30 to 0.15 when the spectrum became softer; meanwhile the inner disk temperature (Tin) increased from 0.2 to 0.45 keV. These results imply that the softening events are triggered by a short-term increase of the mass accretion rate. During the observed spectral softening events, the disk flux (F) and Tin did not obey the relation: F is proportional to Tin^4, suggesting that the inner disk radius does not reach the innermost stable circular orbit.

arXiv comment11 pages, 10 figures, PASJ, accepted

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Cited by in corpus (12)

• WATCHDOG: A Comprehensive All-Sky Database of Galactic Black Hole X-ray Binaries
• The gas-to-extinction ratio and the gas distribution in the Galaxy
• The INTEGRAL view on Black Hole X-ray Binaries
• A low-luminosity soft state in the short period black hole X-ray binary Swift J1753.5-0127
• Expanding hot flow in the black hole binary SWIFT J1753.5-0127: evidence from optical timing
• No evidence for a low-mass black hole in Swift J1753.5-0127
• Disk-Jet quenching of the Galactic Black Hole Swift J1753.5-0127
• The origin of seed photons for Comptonization in the black hole binary Swift J1753.5-0127
• The origin of UV/optical emission in the black hole low-mass X-ray binary Swift J1753.5-0127
• Long term variability of Swift J1753.5-0127]{Long term variability of Swift J1753.5-0127: X-ray spectral-temporal correlations during state transitions
• Swift/BAT and MAXI/GSC Broadband Transient Monitor
• Broad-band spectral study of LMXB black hole candidate 4U 1957+11 with NuSTAR