XMM-Newton observations of the INTEGRAL X-ray transient IGR J17544-2619

Abstract

On September 17, 2003 INTEGRAL discovered a bright transient source 3° from the Galactic Center, IGR J17544-2619. The field containing the transient was observed by XMM-Newton on March 17 and September 11 and 17, 2003. A bright source, at a position consistent with the INTEGRAL location, was detected by the European Photon Imaging Camera (EPIC) during both September observations with mean 0.5-10keV unabsorbed luminosities of 1.1 × 1035 and 5.7 × 1035 erg s-1 for an (assumed) distance of 8 kpc. The source was not detected in March 2003, with a 0.5-10keV luminosity of <3.8 × 1032 erg s-1. The September 11 and 17 EPIC spectra can be represented by a power-law model with photon indices of 2.25 = 0.15 and 1.42 = 0.09, respectively. Thus, the 0.5-10 keV spectrum hardens with increasing intensity. The low-energy absorption during both September observations is comparable to the interstellar value. The X-ray lightcurves for both September observations show energy dependent flaring which may be modeled by changes in either low-energy absorption or power-law index.