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Chandra Detection of Two New Transient X-Ray Sources in M31

ATEL # 1698; J.L. Galache, M.R. Garcia, M.A.P. Torres, S.S. Murray (CfA), D. Steeghs (U. of Warwick/CfA) and B.F. Williams (U. of Washington)
on 4 Sep 2008; 21:47 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Jose Luis Galache (jlgalache@cfa.harvard.edu)

Subjects: Request for Observations, Binaries, Black Holes, Neutron Stars, Transients

We report the discovery of 2 previously unseen X-ray sources detected in a 5ks Chandra/ACIS observation starting on 2008-09-01.32 UT as part of our ongoing Chandra/HST M31 transient program (see also ATel #1693 for more results from this observation). Due to the low count-rate, no spectral fitting was possible. The reported luminosities have been estimated assuming an absorbed power law spectrum with nH = 6.67e20 atoms/cm2 (the Galactic value towards M31), Γ = 1.7 and a distance of 780 kpc. The coordinates are subject to the standard boresight correction.

CXOM31 J004152.9+411322
Coordinates are RA(J2000) 00:41:52.9, Dec(J2000) +41:13:22.2, with centroiding errors of 3.8" and 5.6", respectively. The large uncertainties in the position are due to the source falling on the edge of the ACIS-I chip. The luminosity in the 0.3-8 keV range is 1.5e37 erg/s. The presence of a soft component (93% of the counts are below 2keV) suggests that this may be a black hole transient, although given its luminosity it may also be an accreting neutron star.

CXOM31 J004249.2+411609
Coordinates are RA(J2000) 00:42:49.2, Dec(J2000) +41:16:00.9, with centroiding errors of 0.15" and 0.27", respectively. The luminosity in the 0.3-8 keV range is 1.4e37 erg/s. This luminosity and a harder spectrum (only 58% of the counts are below 2 keV and the spectrum extends up to 6 keV) would be consistent with this source being an accreting neutron star.

Further optical and X-ray observations of these sources are encouraged.


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