Outbursts of the intermediate-mass black hole HLX-1: a wind instability scenario

Understand

We model the intermediate-mass black hole HLX-1, using the Hubble Space Telescope, XMM-Newton and Swift.

• We quantify the relative contributions of a bluer component, function of X-ray irradiation, and a redder component, constant and likely coming from an old stellar population.
• We estimate a black hole mass of about (2^{+2}_{-1}) x 10^4 M_{sun}, a spin parameter a/M ~ 0.9 for moderately face-on view, and a peak outburst luminosity of about 0.3 times the Eddington luminosity.
• We discuss the discrepancy between the characteristic sizes inferred from the short X-ray timescale (R ~ a few 10^{11} cm) and from the optical emitter (R sqrt[cos theta] ~ 2.2 x 10^{13} cm).