New X-Ray Transient in M31: CXOM31 J004059.2+411551
ATel #1147; J. L. Galache, M. R. Garcia, D. Steeghs, M. A.P. Torres, S. S. Murray, F. A. Primini (CfA) and B. F. Williams (U. of Washington)
on 19 Jul 2007; 15:44 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jose Luis Galache (jlgalache@cfa.harvard.edu)
Subjects: Binary, Black Hole, Transient
Referred to by ATel #: 1191
We report the discovery of a previously unseen X-ray point source detected in a 5ks observation starting on 2007-07-05.54 UT as part of our ongoing Chandra/HST M31 transient program. The source was detected on the edge of ACIS-S at coordinates RA(J2000) 00:40:59.2, Dec(J2000) +41:15:51.2, with centroid position errors of 2.4" and 3.0", respectively (subject to the standard bore-sight correction).
The 0.7-3.0 keV spectrum is well modelled using an absorbed disk blackbody (after ascertaining that an added powerlaw made a negligible contribution to the flux). Leaving all parameters free we find the best fit with nH = 2.3e21 atoms/cm2 and Tin ~ 0.46 keV. We note that this nH is substantially larger than the galactic contribution along the line of sight. The equivalent unabsorbed luminosity (assuming a distance of 780 kpc to M31) is Lx ~ 7.5e37 erg/s in the 0.5-10 keV range.
The presence of a very soft component in the spectrum and the X-ray luminosity are consistent with the source being a black hole transient in a thermal (high-soft) state. Further optical and X-ray observations of this source are encouraged.
