We re-assess the XMM-Newton and Swift observations of HLX1, to examine the evidence for its identification as an intermediate-mass black hole. We show that the X-ray spectral and timing properties are equally consistent with an intermediate-mass black hole in a high state, or with a foreground neutron star with a luminosity of about a few times 10^{32} erg/s ~ 10^{-6} L_{Edd}, located at a distance of about 1.5 to 3 kpc. Contrary to previously published results, we find that the X-ray spectral change between the two XMM-Newton observations of 2004 and 2008 (going from power-law dominated to thermal dominated) is not associated with a change in the X-ray luminosity. The thermal component becomes more dominant (and hotter) during the 2009 outburst seen by Swift, but in a way that is consistent with either scenario.
@article{arxiv.1008.3382,
title = {X-ray study of HLX1: intermediate-mass black hole or foreground neutron star?},
author = {Roberto Soria and Luca Zampieri and Silvia Zane and Kinwah Wu},
journal= {arXiv preprint arXiv:1008.3382},
year = {2015}
}
Comments
10 pages, accepted by MNRAS. Corrected LZ's affiliation and updated 1 reference