Eccentricity of HLX-1

Abstract

I compare the outer radius of the accretion disc in the intermediate-mass black hole candidate HLX-1 as estimated from the UV/optical continuum, with the values estimated from its outburst decline timescales. I fit the Swift 2010 outburst decline lightcurve with an exponential decay, a knee and a linear decay. I find that the disk has an outer radius 10^{12} cm <~ R_{out} <~ 10^{13} cm, only an order of magnitude larger than typical accretion discs in the high/soft state of Galactic black holes. By contrast, the semimajor axis is ~ a few times 10^{14} cm. This discrepancy can be explained with a highly eccentric orbit. I estimate the tidal truncation radius and circularization radius around the black hole at periastron, and impose that they are similar to or smaller than the outer disk radius. I obtain that e >~ 0.95, that the radius of the donor star is <~ a few solar radii, and that the donor star is not at risk of tidal disruption. If the companion star fills its Roche lobe and impulsively transfers mass only around periastron, secular evolution of the orbit is expected to increase eccentricity and semimajor axis even further. I speculate that such extremely eccentric systems may have the same origin as the S stars in the Galactic centre.

6 pages, 170 KB, accepted by MNRAS

References in corpus (10)

• An online repository of Swift/XRT light curves of GRBs
• Radio Detections During Two State Transitions of the Intermediate Mass Black Hole HLX-1
• X-ray Variability and Hardness of ESO 243-49 HLX-1: Clear Evidence for Spectral State Transitions
• Interacting Binaries with Eccentric Orbits. Secular Orbital Evolution Due To Conservative Mass Transfer
• Interacting Binaries with Eccentric Orbits II. Secular Orbital Evolution Due To Non-Conservative Mass Transfer
• A Young Massive Stellar Population Around the Intermediate Mass Black Hole ESO 243-49 HLX-1
• Origin of the S Stars in the Galactic Center
• Optical counterpart of HLX-1 during the 2010 outburst
• Mass transfer during low mass X-ray transient decays
• A minor merger scenario for the ultraluminous X-ray source ESO 243-49 HLX-1

Cited by in corpus (13)

• Ultraluminous X-Ray Sources
• Ultraluminous X-ray sources
• The Close Stellar Companions to Intermediate Mass Black Holes
• Kinematics of the intermediate mass black hole candidate HLX-1
• Combined Analysis of Hubble and VLT Photometry of the Intermediate Mass Black Hole ESO 243-49 HLX-1
• Outbursts of the intermediate-mass black hole HLX-1: a wind instability scenario
• ESO 243-49 HLX-1: scaling of X-ray spectral properties and black hole mass determination
• Simulations of the tidal interaction and mass transfer of a star in an eccentric orbit around an intermediate-mass black hole: the case of HLX-1
• X-ray outbursts of ESO 243-49 HLX-1: comparison with Galactic low-mass X-ray binary transients
• Long-term X-ray Variability of Ultraluminous X-ray Sources
• Spectral index-mass accretion rate correlation and evaluation of black hole masses in AGNs 3C~454.3 and M87
• A disrupted bulgeless satellite galaxy as counterpart of the ultraluminous X-ray source ESO 243-49 HLX-1
• Accretion disk parameters in HLX-1