New X-ray Outburst of ESO 243-49 HLX-1
ATel #6916; A. K.H. Kong (NTHU, Taiwan), R. Soria (ICRAR-Curtin), S. Farrell (Univ. Sydney)
on 14 Jan 2015; 07:55 UT
Credential Certification: Albert Kong (akong@phys.nthu.edu.tw)
Subjects: X-ray, Black Hole
Referred to by ATel #: 10289
We report on recent Swift/XRT observations of the intermediate-mass black hole candidate ESO 243-49 HLX-1 (Farrell et al. 2009). Swift/XRT has been performing regular monitoring observations of HLX-1 to catch the yearly recurrent X-ray outbursts. The last X-ray outburst occurred in 2013 early October (ATel #5439). On 2015-Jan-08, HLX-1 showed indication of X-ray excess against the background in a 1.3 ks XRT observation with a background-subtracted 0.3-10 keV count rate of 0.003 c/s. On 2015-Jan-13, HLX-1 is clearly seen with a count rate of 0.0079+/-0.0029 c/s. Seven out of eight detected X-ray photons come from below 1.5 keV. This count rate is consistent with the beginning of the last outburst in 2013 (ATel #5439). Assuming an absorbed power-law model with a photon index of 2.5 and N_H=4E20 cm^-2, HLX-1 has already reached Lx ~ 3E41 erg/s on Jan 13, and that if it follows the behaviour of previous outbursts, will become ~4 times as bright.
HLX-1 has been shown to have recurrent outbursts with an outburst interval changing from ~370 days to ~400 days (see e.g., Kong 2011, arXiv:1102.3212; Lasota et al. 2011; ATel #5439). If the X-ray excess on 2015-Jan-08 marks the beginning of a new outburst, the interval between the two outbursts is 463 days, suggesting that the outburst cycle is becoming longer.
Multiwavelength follow-up observations are strongly encouraged.
