bright ULX or a recoiling super-massive black hole in CXO J122518.6+144545

In this Paper we report the discovery of CXO J122518.6+144545; a peculiar X-ray source with a position 3.6±0.2′ ′ off-nuclear from an SDSS DR7 z=0.0447 galaxy. The 3.6′ ′ offset corresponds to 3.2 kpc at the distance of the galaxy. The 0.3–8 keV X-ray flux of this source is 5×10−14 erg cm−2 s−1 and its 0.3–8 keV luminosity is 2.2×1041 erg s−1 (2.7×1041 erg s−1; 0.5–10 keV) assuming the source belongs to the associated galaxy. We find a candidate optical counterpart in archival HST/ACS g′– band observations of the field containing the galaxy obtained on June 16, 2003. The observed magnitude of g ′ = 26.4±0.1 corresponds to an absolute magnitude of −10.1. We discuss the possible nature of the X-ray source and its associated candidate optical counterpart and conclude that the source is either a very blue type IIn supernova, a ULX with a very bright optical counterpart or a recoiling super-massive black hole