XMM - Newton observations of the INTEGRAL X - ray transient IGR J 17544 − 2619

On 2003 September 17 INTEGRAL discovered a bright transient source 3◦ from the Galactic Center, IGRJ17544−2619. The field containing the transient was observed by XMM-Newton on 2003 March 17 and September 11 and 17. 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 0.5–10 keV unabsorbed luminosities of 1.1×10 and 5.7×10 erg s for an (assumed) distance of 8 kpc. The source was not detected in 2003 March with a 0.5–10 keV luminosity of <3.8×10 erg s. 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±0.17, 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.