A new soft X-ray transient from the XMM-Newton slew survey
ATel #1537; R. Saxton(ESAC), P. Esquej(MPE), P. Evans(LU), J. Osborne(LU), K. Page(LU), A. Read(LU), M. Sanchez(ESAC)
on 20 May 2008; 09:16 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Richard Saxton (richard.saxton@sciops.esa.int)
Subjects: Optical, X-ray, Request for Observations, Transient
We report the discovery of a new soft X-ray transient, XMMSL1 J072822.2+745406,
found in an XMM-Newton slew of April 26th. The source position is
RA: 07 28 22.2 DEC: 74 54 06 with an 8", 1 sigma, error circle.
The source count rate was 1.1 c/s in the EPIC-pn detector and the spectrum is soft
with no events above 2 keV. The unabsorbed flux is
2.3E-12 ergs/s/cm^2 (0.2-2 keV; for a black-body spectral model of
temperature 130eV and galactic absorption of NH=3.75E20). This flux is 24x greater
than an upper-limit calculated from the ROSAT All Sky Survey using the same
spectral parameters.
One catalogued optical source, EO1295-0467919, lies within the error circle with a
magnitude m_b=20.1, m_r=18.3. This source is flagged as extended in the APM catalogue.
An optical spectrum was taken by the WHT on May 13 with the ISIS spectrometer using the
R158R and R158B low-resolution gratings. The Ca II H and K, H_beta, H_delta, H_gamma
absorption lines can be identified and have a redshift consistent with zero. i.e. the object
is located within our galaxy.
A Swift XRT observation was performed on May 15 for 2.4ks and confirmed the
source at a position: RA: 07 28 21.95, DEC: +74 54 02.4 (error 2.0", 90% confidence),
still consistent with EO1295-0467919. The extrapolated 0.2-2 keV unabsorbed
flux is 1.2E-12 ergs/s/cm^2 implying that the
source has faded by a factor ~1.8 since the slew observation. The Swift XRT spectrum
is soft and can be fit by a power-law of slope 3.7+/-0.5 or a black-body of
temperature 130+/-20 eV.
The source type remains unknown. If it is a star then the spectral type will be F or G and
given the magnitudes, the distance would be a few kpc and the Luminosity high for
a stellar coronal event.
We welcome further observations in particular to
investigate the reported extended optical emission.
