Discovery of a second outbursting hyperluminous X-ray source

Abstract

We report on six Chandra and one HST/WFC3 observation of CXO J122518.6+144545, discovered by Jonker et al. (2010) as a candidate hyperluminous X-ray source (HLX), X-ray bright supernova or recoiling supermassive black hole at $L_X=2.2\times 10^{41}$ erg/s (if associated with the galaxy at 182 Mpc). We detect a new outburst of the source in a Chandra image obtained on Nov 20, 2014 and show that the X-ray count rate varies by a factor $>60$. New HST/WFC3 observations obtained in 2014 show that the optical counterpart is still visible at $g^{\prime }=27.1\pm 0.1$, $1\pm 0.1$ magnitude fainter than in the discovery HST/ACS observation from 2003. This optical variability strongly suggests that the optical and X-ray source are related. Furthermore, these properties strongly favour an HLX nature of the source over the alternative scenarios. We therefore conclude that CXO J122518.6+144545 is most likely an outbursting HLX. It is only the second such object to be discovered, after HLX-1 in ESO 243-49. Its high X-ray luminosity makes it a strong candidate to host an intermediate mass black hole.

5 pages, 1 table, 1 figure, accepted for publication in MNRAS Letters

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Cited by in corpus (8)

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• NIR Counterparts to ULXs (III): Completing the photometric survey and selected spectroscopic results
• Discovery of the Candidate Off-nuclear Ultrasoft Hyper-luminous X-ray Source 3XMM J141711.1+522541
• Discovery of a transient ultraluminous X-ray source in the elliptical galaxy M86
• Characterisation of a candidate dual AGN
• Prospects for Revealing Intermediate-Mass Black Holes in NGC 1399 using SKA
• A likely inverse-Compton emission from the Type IIb SN 2013df