XMMU J004243.6+412519 - a new X-ray transient in M 31 seen with XMM-Newton
ATel #3890; M. Henze, W. Pietsch, F. Haberl (all MPE) and the XMM-Newton/Chandra M 31 nova monitoring collaboration
on 26 Jan 2012; 16:54 UT
Credential Certification: Martin Henze (mhenze@mpe.mpg.de)
Subjects: X-ray, Transient
On behalf of the XMM-Newton/Chandra M 31 nova monitoring collaboration (see http://www.mpe.mpg.de/~m31novae/xray/ao10/index.php ) we report the discovery of a new bright X-ray transient in M 31 in a 20 ks XMM-Newton EPIC observation which started on 2012-01-15.62 UT. The source position is R.A.(J2000) = 00:42:43.59, Dec.(J2000) = +41:25:19.3 (1 sigma error of 2.4 arcsec), using the catalogue of Kaaret (2002, ApJ, 578, 114) as an astrometric reference. No X-ray source was known previously within 30 arcsec of the new transient, which is designated XMMU J004243.6+412519.
The EPIC pn light curve of the source indicates variability by about a factor of two on time scales of 100 s, but no periodicity could be found. For the X-ray spectrum of XMMU J004243.6+412519 the best fit (reduced chi-squared of 0.99) is achieved using an absorbed powerlaw with absorption column density of (3.8+/-0.4)e21 cm-2 and a powerlaw index of 2.0+/-0.1. This model results in an unabsorbed luminosity of 2.1e38 erg/s, assuming a distance to M 31 of 780 kpc. XMMU J004243.6+412519 can most likely be classified as a low-mass X-ray binary (LMXB) in M 31 with a luminosity close to the Eddington limit of a neutron star. The large best-fit column density (Galactic foreground: 6.7e20 cm-2) suggests that the source, which is situated approximately 10 arcmin north of the M 31 centre, might experience strong extinction from being located behind an inner spiral arm of the galaxy.
