Hint for a faint intermediate mass black hole in the Ursa Minor dwarf galaxy

We report the results of the analysis of an archive Chandra observation of the Ursa Minor spheroidal galaxy,. one of the closest Milky Way satellites, searching for signatures from the intermediate mass black hole possibly hosted in the center of the galaxy. We identified an X-ray source with a detection confidence as low as similar or equal to 2.5 sigma and with an estimated unabsorbed flux in the 0.5-7 key band of similar or equal to 4.9 x 10(-15) erg s(-1) cm(-2) and at a few arcseconds from the reported center of the galaxy. The source is spatially coincident with a radio object (having flux density of similar or equal to 7.1 mJy at 1.4 GHz) already observed in the NRAO VLA Sky Survey. In the accreting black hole scenario, depending on the used fundamental plane relation, one estimates an accretor mass of (2.9(-2.7)(+33.06)) x 10(6) M-circle dot or (11.7(-9.7)(+57.1)) x 10(6) M-circle dot. Relaxing the assumption for a flat radio spectrum, the minimum black hole mass would result in the range 5 x 10(4) M-circle dot - 5 x 10(5) M-circle dot, i.e. still consistent with an intermediate mass black hole scenario. The compact object seems to radiate at a very tiny fraction of the associated Eddington luminosity. (C) 2013 Elsevier B.V. All rights reserved.