Swift J004346.0+410736, an X-ray transient in M 31
ATel #6454; R. Sturm, W. Pietsch, J. Greiner, F. Haberl (MPE, Germany)
on 9 Sep 2014; 14:23 UT
Credential Certification: Richard Sturm (rsturm@mpe.mpg.de)
Subjects: X-ray, Binary, Black Hole, Neutron Star, Transient
We report the discovery of an X-ray transient (Swift J004346.0+410736)
in monitoring observations of the central region of the Andromeda Galaxy (M 31)
with the XRT on board the Swift satellite.
The source is detected in two recent observations (ObsID 00032702074 and 00032702075) on 2014-09-03 from 18:57 to 22:15 (UT) and 2014-09-07 from 01:14 to 04:50
with 18.2±7.2 net counts in 3840 s net exposure and 12.2±5.9 net counts in 3813 s exposure, respectively.
The coordinates are RA=00:43:46.0 and Dec=+41:07:36 (J2000, total uncertainty 5.6").
The source was likely detected during an XMM-Newton observation on 2010-12-26 at a similar flux and is listed as 3XMM J004346.0+410738 (angular separation: 2.1").
However, the source was observed far off-axis with EPIC-pn only and close to Nova M31N 2010-09b.
It was not detected in the following XMM-Newton observation nine days later.
We found no other detection or classification of this source.
Also in the UVOT, no source is seen with the uvw1 filter.
By fitting an absorbed power-law model with C statistics in the 0.3-5.0 keV band,
we estimate a photon index of Γ=2.5 (1.4-3.8),
an absorbing column density of NH=2.6 (0.14-6.0)×1021cm-2,
and fluxes of 1.5 (1.0-2.3) and 1.3 (0.8-2.1) × 10-13erg cm-2 s-1.
For a source in M 31 (780 kpc distance), this corresponds to an unabsorbed luminosity of 2.5 and 2.2 × 1037erg s-1.
Alternatively, for a disk black-body spectrum, we find
NH=0.5 (0-2.5)×1021cm-2
and kT=0.90 (0.58-1.8) keV.
The X-ray spectrum and duration of the outburst suggest an X-ray binary in M 31.
All uncertainties are given for 90% confidence.
We would like to thank the Swift Team for making these observations possible, in particular N. Gehrels, the duty scientists, as well as the science planners.