Swift Follow-up of 4U 1630-47 in Outburst

ATel #15575; Jiachen Jiang (Cambridge), John Tomsick (UCB), Honghui Liu (Fudan Uni.), Andrew Fabian (Cambridge), Riley Connors (Caltech), Javier Garcia (Caltech), Jeremy Hare (Goddard)
on 27 Aug 2022; 17:01 UT
Credential Certification: Jiachen Jiang (jj447@cam.ac.uk)

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4U 1630-47 is a recurrent X-ray transient first discovered by Uhuru. Although some details of the binary system remain uncertain, its X-ray spectral and timing behaviours suggest a black hole candidate as the nature of the compact accretor. This object recently started a new outburst on 28 July 2022 as alerted by MAXI (ref). The MAXI monitoring program shows that the X-ray intensity (2-20 keV) reached the peak on 21 Aug 2022 at 0.8 cts/cm2/s and has been decaying since then. The daily average MAXI count rate is 0.66 cts/cm2/s on 24 Aug. The X-ray hardness defined as the MAXI count rate ratio between the 4-10 and 2-4 keV bands increased from 0.93 on 21 Aug to 1.18 on 24 Aug. We requested the first Swift observation of 4U 1630-472 during this outburst on 25 Aug. The XRT was operated in the Window Timing mode and received an average count rate of 29 cts/s. The XRT spectrum is best described by an absorbed disk blackbody model (diskbb). The line-of-sight column density is 7.72+/-0.14e22 cm-2. The inner temperature of the disk blackbody is 1.51+/-0.03 keV and the normalization parameter is 110+/-10. The 0.5-10 keV absorbed (unabsorbed) flux of this object is 4.03e-9 (1.14e-8) erg/cm2/s. We thank the Swift PI Brad Cenko for approving this ToO request. Ref: http://maxi.riken.jp/alert/novae/9788849996/9788849996.htm.

4U 1630-47 MAXI page