Confirmation of IGR J01363+6610 as a Be X-ray Binary with very low quiescent X-ray luminosity

Abstract

The field containing the candidate High Mass X-ray Binary IGR J01363+6610 was observed by XMM-Newton on 2009 July 31 for 28 ks. A Be star was previously suggested as the possible counterpart of the INTEGRAL source, and although Chandra, during a 2007 observation, did not detect an X-ray source at the position of the Be star, we find a variable source (XMMU J013549.5+661243) with an average X-ray flux of 2 × 10-13 erg cm -2 s -1 (0.2-12 keV, unabsorbed) at this position with XMM-Newton. The spectrum of this source is consistent with a hard power law with a photon index of T = 1.4 ± 0.3 and a column density of NH = (1.5 +0.7-0.5) × 1022cm -2 (90% confidence errors). These results, along with our optical investigation of other X-ray sources in the field, make the association with the Be star very likely, and the 2 kpc distance estimate for the Be star indicates an X-ray luminosity of 9.1 × 1031 erg s-1. This is lower than typical for a Be X-ray binary, and the upper limit on the luminosity was even lower (<1.4 × 1031 ergs-1 assuming the same spectral model) during the Chandra observation. We discuss possible implications of the very low quiescent luminosity for the physical properties of IGR J01363+6610. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.