New X-ray Outburst of ESO 243-49 HLX-1
ATel #4332; A. K.H. Kong (NTHU/Caltech)
on 24 Aug 2012; 00:25 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Albert Kong (akong@phys.nthu.edu.tw)
Subjects: X-ray, Black Hole, Transient
Following the initial alert of a possible re-brightening of the intermediate-mass black hole candidate ESO243-49 HLX-1 (Godet et al. 2012, ATel #4327), we analyzed the most updated Swift XRT data taken on 2012 August 23 between 15:22:51 and 15:38:54 UT. The XRT observation was taken in the photon counting mode with an exposure of 943 sec. HLX-1 is clearly detected with 17 X-ray photons in the 0.3-10 keV band. This is a factor of 3 increase comparing to the previous observation taken on 2012 August 21 (ATel #4327). We therefore confirm that HLX-1 has begun a new outburst. The previous outburst started in 2011 mid-August (ATel #3564, #3569) implying that the interval between the two outbursts is about 375 days. This is consistent with the expected recurrent period (Kong 2011, arXiv:1102.3212; Lasota et al. 2011).
The new Swift data also show that 16 out of 17 X-ray photons are from the 0.3-1.5 keV indicating that the source is soft, a typical behavior of a black hole binary in outburst. We analyzed the X-ray spectrum with unbinned data and C-statistic. With an absorbed power-law with a fixed N_H=4e20 cm^-2, the best-fit photon index is 3.6+/-0.8 (90% confidence) and the unabsorbed 0.3-10 keV luminosity is 1e42 erg/s assuming a distance of 95 Mpc. We also fit the spectrum with an absorbed disk blackbody (diskbb in XSPEC) model, the best fit temperature is 0.21(+0.08, -0.05) keV and the unabsorbed 0.3-10 keV luminosity is 8e41 erg/s. In spite of the low photon statistic, the result is roughly consistent with previous outbursts (see Servillat et al. 2011).
Multiwavelength follow-up observations are strongly encouraged.
