Detection of X-Ray Elongated Emission From an Ultraluminous X-Ray Source in the Interacting Pair of Galaxies NGC 5953/5954

Abstract

We present radio through X-ray results of a bright (> 10 40 ergs s −1 in the 0.5 to 8.0 keV band) ultraluminous X-ray source (ULX), CXOU J153434.9+151149, in the starburst, interacting pair of galaxies NGC 5953/5954. Chandra image of this ULX shows that it is elongated. From HST/WFPC2/F606W data we have detected a counterpart of the ULX system with M F 606W ∼ -7.1±0.7 mag. This optical counterpart may be either an O-type supergiant star or a young star cluster. From our Fabry-Perot interferometric observations, we have detected Hα and [NII] (λ6584Å) diffuse emission, with velocity gradients up to 60 km s −1 at the astrometric corrected Chandra position of the ULX. Different scenarios have been invoked as to explain the possible nature of CXOU J153434.9+151149.Based on the observed X-ray morphology of the ULX, we determine that the inclination angle to the elongated emission will be ∼53 o . Beaming with this geometry from a stellar-mass black hole system will be inadequate to explain the observed X-ray luminosity of this ULX. Finally, we suggest that mild-beaming from a binary black hole with mass more than 50M ⊙ associated with a young star cluster, is the most favorable scenario that describes the multiwavelength properties of this ULX. Future observations are highly essential to determine the nature of this rare object.

Irradiated, colour-temperature-corrected accretion discs in ultraluminous X-ray sources

“…Indeed, point-like optical counterparts have been identified for a number of ULXs (Goad et al 2002;Liu, Bregman & Seitzer 2002;Kaaret et al 2004;Liu, Bregman & Seitzer 2004;Kuntz et al 2005;Mucciarelli et al 2005;Soria et al 2005;Liu et al 2007;Grisé et al 2008Grisé et al , 2011Roberts, Levan & Goad 2008;Rosado, Ghosh & Fuentes-Carrera 2008;Gladstone et al 2013), many of which are blue in colour, and appear to be consistent with large early-type companions, although a minority of the potential counterparts in the sample of Gladstone et al (2013) have colours which rule out O-type stars. However, it may not be possible to trivially identify stellar counterparts to ULXs.…”

“…Irrespective of the precise nature of the central black hole and its accretion state, ULXs must have a large reservoir of mass to accrete from, in order to produce their observed X-ray luminosities. Indeed, point-like optical counterparts have been identified for a number of ULXs (Goad et al 2002;Liu et al 2002;Kaaret et al 2004;Liu et al 2004;Soria et al 2005;Kuntz et al 2005;Mucciarelli et al 2005;Liu et al 2007;Grisé et al 2008;Roberts et al 2008;Rosado et al 2008;Grisé et al 2011;Gladstone et al 2013), many of which are blue in colour, and appear to be consistent with large early-type companions; although a minority of the potential counterparts in the sample of Gladstone et al (2013) have colours which rule out O-type stars. However, it may not be possible to trivially identify stellar counterparts to ULXs.…”