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Detection of a new X-ray transient in a globular cluster in M31

ATel #1296; F. Haberl (Max-Planck-Institut fuer extraterrestrische Physik, MPE), M. Henze (MPE), W. Pietsch (MPE)
on 21 Nov 2007; 15:08 UT
Credential Certification: Frank Haberl (fwh@mpe.mpg.de)

Subjects: X-ray, Black Hole, Globular Cluster, Nova, Neutron Star, Transient

Referred to by ATel #: 1306, 1328, 1334

On behalf of the XMM-Newton/Chandra M31 nova monitoring collaboration (see http://www.mpe.mpg.de/~m31novae/xray/ao6/index.php ) we report the discovery of a new X-ray transient in a 20 ks observation starting on 2007-11-07.64 UT. The source was detected at a large off-axis angle in the Chandra HRC-I at coordinates RA(J2000) 00:43:45.17, Dec(J2000) +41:06:09.0, with centroid position errors of 0.5" and 0.4", respectively (subject to the standard bore-sight correction).

We detected 426+/-43 cts which corresponds to a vignetting-corrected 0.2 - 10 keV flux of 6e-13 erg/cm2/s assuming an absorbed power-law spectrum (NH 6e20 cm-2, photon index 1.7). The absorbed luminosity in this band is 9e37 erg/s (for a distance of 780 kpc to M31). The position of the source coincides with the M31 globular cluster Bol 194 (see e.g. Galleti et al. 2006, A&A 456, 985). In the following 20 ks observation of the HRC monitoring campaign starting on 2007-11-17.76 UT the source was again detected with similar brightness close to the edge of the field of view.

Due to the current lack of X-ray spectral information the nature of the transient can not be uniquely constrained. The X-rays may originate in a black hole or neutron star low mass X-ray binary or from an optical nova in the globular cluster (similar to M31N 2007-06b; Pietsch et al. 2007, ATel #1294).