Swift observations show that H1743-322 is on its way to quiescence after the recent outburst

ATel #10751; Chichuan Jin (MPE, Germany), Gabriele Ponti (MPE, Germany), Tomaso Belloni (INAF/OAB, Italy), Barbara De Marco (NCAC, Poland), Arne Rau (MPE, Germany), Rob Fender (Oxford University, UK), Teo Munoz-Darias (IAC-Tenerife, Spain), Mickael Coriat (IRAP, France)
on 15 Sep 2017; 13:49 UT
Credential Certification: Chichuan Jin (chichuan@mpe.mpg.de)

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A new outburst of the black hole transient H1743-322 was reported in 2017-07-27 by Zhang et al. (ATel#10599) using Swift/BAT monitoring. This was also confirmed by the MAXI light curves. Then we used the Swift/XRT to monitor the source in order to follow its spectral state evolution during the outburst. This includes 14 observations in the XRT Window Timing (WT) mode between 2017-08-05 and 2017-09-06, for an average exposure time of ~1 ks per observation. The XRT spectra between 0.5-10 keV were well fitted by an absorbed power law model, with the Hydrogen column density (nH) being fixed at 2.4E+22 cm^-2 (Dunn et al. 2010). The last Swift/XRT observation of H1743-322 previous to our monitoring was carried out in 2016-04-08. This showed that the source had an unabsorbed 3-10 keV flux of F(3-10keV)=(1.03+/-0.05)*E-10 erg/s/cm2, with a 0.5-10 keV power law photon index of PI=1.35+/-0.11, and a hardness ratio (i.e. the unabsorbed flux ratio between 6-10 keV and 3-6 keV) of R_HR=1.09+/-0.07, together with the MAXI light curves, indicating that the source was returning to quiescence after the outburst reported in 2016-02-28 (Lin et al. ATel#8751). In 2017-08-05, Swift/XRT observation showed that the source had F(3-10keV)=(9.47+/-0.13)*E-10 erg/s/cm2 with PI=1.69+/-0.03 and R_HR=0.89+/-0.02, which was one order of magnitude brighter and softer than in the previous Swift/XRT observation in 2016-04-08, therefore confirming the new outburst (Zhang et al. ATel#10599). Then the source continued to show marginal flux increasing and spectral softening until 2017-08-16, when it reached F(3-10keV)=(9.94+/-0.22)*E-10 erg/s/cm2, PI=1.84+/-0.05 and R_HR=0.81+/-0.03, indicating the source to be still in the hard state. Then the source was found to decay rapidly until the last Swift/XRT observation in 2017-09-06, when it had F(3-10keV)=(1.33+/-0.06)*E-10 erg/s/cm2, PI=1.63+/-0.10 and R_HR=0.92+/-0.05, indicating a flux level similar to that observed in 2016-04-08. Therefore, it appears that H1743-322 is already on its way back to quiescence after the new outburst.

This is the hardness intensity diagram of the new outburst monitored by Swift/XRT, overlaid on the RXTE data published by Dunn et al. (2010).