Swift J004249.5+411212, a new X-ray transient in M 31
ATel #7048; C. Delvaux, P. Schady, W. Pietsch, F. Haberl, J. Greiner (MPE)
on 11 Feb 2015; 11:48 UT
Credential Certification: Wolfgang Pietsch (wnp@mpe.mpg.de)
Subjects: X-ray, Binary, Black Hole, Neutron Star, Transient
Referred to by ATel #: 7054
In recent monitoring observations of the Andromeda Galaxy with the X-Ray
Telescope (XRT) onboard the Swift satellite from 2015-01-25 to 2015-02-10,
we find a new X-ray transient (Swift J004249.5+411212) at RA=00:42:49.50
Dec=+41:12:12.3 (J2000, ePOS=3.5"), at 4.10' of the center of Andromeda Galaxy.
There is no X-ray source present at this position in previous M 31 X-ray
catalogues.
The following table gives the observation ID, the exposure time, the date
and start time of the observations, count rates and and
2-sigma statistical uncertainties:
ObsID Exp Date Time Count rate
[ks] (MJD) (/s)
00031283028 4038 2015-01-17 57039.46 <0.003
00031283029 3912 2015-01-25 57047.31 0.004±0.001
00031283030 4110 2015-02-02 57055.24 0.009±0.002
00080007001 12374 2015-02-06 57059.97 0.007±0.001
00080007002 3586 2015-02-08 57061.02 0.008±0.002
00031283031 3219 2015-02-10 57063.55 <0.002
By fitting an absorbed power law to the 54 photons detected in ObsID
00080007001,
we estimate an N
H=8.7±5.8
×10
20cm
-2 and Γ=1.7±0.2, as well
as an average flux of 3.5 × 10
-13erg cm
-2
s
-1 in the 0.3-5.0 keV band.
For a source in M 31 (780 kpc distance), this corresponds to an unabsorbed
luminosity of 3.2 × 10
38erg s
-1 in the 0.3-5.0 keV band.
Such a luminosity could be consistent with a LMXB transient containing a neutron star or a black hole.
In a stack of all UVOT/uvm2 filter observations on 2015-02-06 we do not
detect any counterpart candidate within the X-ray position down to a
2-sigma limit of m2_AB>23.1.
The last observations suggest that the outburst has reached its maximum
brightness and has faded down to the detection threshold of Swift/XRT after 16 days.
We strongly encourage further multi-wavelength observations of Swift
J004249.5+411212, in particular deeper optical imaging and radio
observations, to identify the counterpart of this new X-ray transient.
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.