Investigating the mass of the intermediate mass black hole candidate HLX-1 with the slimbh model

Abstract : In this paper we present a comprehensive study of the mass of the intermediate mass black hole candidate HLX-1 in the galaxy ESO 243-49. We analyse the continuum X-ray spectra collected by Swift, XMM-Newton, and Chandra with the slim disc model, slimbh, and estimate the black hole mass for the full range of inclination (inc = 0°−85°) and spin (a∗ = 0−0.998). The relativistic slimbh model is particularly suited to study high luminosity disc spectra as it incorporates the effects of advection, such as the shift of the inner disc edge towards smaller radii and the increasing height of the disc photosphere (including relativistic ray-tracing from its proper location rather than the mid-plane of the disc). We find for increasing values of inclination that a zero spin black hole has a mass range of 6300−50 900 M⊙ and a maximally spinning black hole has a mass between 16 900−191 700 M⊙. This is consistent with previous estimates and reinforces the idea that HLX-1 contains an intermediate mass black hole.