X-Ray Outbursts of ESO 243-49 HLX-1: Comparison with Galactic Low-mass X-Ray Binary Transients
Abstract
We studied the outburst properties of the hyper-luminous X-ray source ESO 243-49 HLX-1, using the full set of Swift monitoring observations. We quantified the increase in the waiting time, recurrence time, and e-folding rise timescale along the outburst sequence, and the corresponding decrease in outburst duration, total radiated energy, and e-folding decay timescale, which confirms previous findings. HLX-1 spends less and less time in outburst and more and more time in quiescence, but its peak luminosity remains approximately constant. We compared the HLX-1 outburst properties with those of bright Galactic low-mass X-ray binary transients (LMXBTs). Our spectral analysis strengthens the similarity between state transitions in HLX-1 and those in Galactic LMXBTs. We also found that HLX-1 follows the nearly linear correlations between the hard-to-soft state transition luminosity and the peak luminosity, and between the rate of change of X-ray luminosity during the rise phase and the peak luminosity, which indicates that the occurrence of the hard-to-soft state transition of HLX-1 is similar to those of Galactic LMXBTs during outbursts. We found that HLX-1 does not follow the correlations between total radiated energy and peak luminosity, and between total radiated energy and e-folding rise/decay timescales we had previously identified in Galactic LMXBTs. HLX-1 would follow those correlations if the distance were several hundreds of kiloparsecs. However, invoking a much closer distance for HLX-1 is not a viable solution to this problem, as it introduces other, more serious inconsistencies with the observations.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2015
- DOI:
- 10.1088/0004-637X/811/1/23
- arXiv:
- arXiv:1508.03155
- Bibcode:
- 2015ApJ...811...23Y
- Keywords:
-
- accretion;
- accretion disks;
- black hole physics;
- X-rays: binaries;
- X-rays: individual: HLX-1;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 13 papges, 12 figures, accepted for publication in ApJ, proof corrections applied