XMM-Newton Monitoring of the Most Luminous Off-Nuclear IMBH Candidate

Intermediate-mass black holes (IMBH, 10^2-10^5 solar mass) have been long sought after because they are predicted to exist in several important astrophysical processes and are also leading candidates for gravitational wave emission. The strongest IMBH candidates are hyperluminous off-nuclear X-ray sources (HLX) with Lx > 10^{41} erg/s, but very few candidates are found around this limit. We have identified a new HLX candidate with an estimated X-ray luminosity of 10^{43} erg/s at a distance about 2 Gpc. Thus it could be the most luminous and the most distant IMBH known and provide strong evidence for IMBH existence. We propose a follow-up observation of the source by XMM-Newton to monitor possible large spectral/flux change as seen in ESO 243-49 HLX-1