Swift observes the XMM-Newton Slew Survey bright transient XMMSL1 J063045.9-603110
ATel #3821; A M Read (University of Leicester), R D Saxton (ESAC), P Esquej (CAB, CSIC-INTA)
on 22 Dec 2011; 17:45 UT
Credential Certification: Dr. Andy Read (amr30@star.le.ac.uk)
Subjects: Ultra-Violet, X-ray, Transient
The new bright soft X-ray source XMMSL1 J063045.9-603110, discovered on 1st
December 2011 by ESA's XMM-Newton in its Slew Survey mode [ATel #3811] has
been observed by Swift on 20th December 2011 for 2.9 ksec.
The Swift-XRT position, enhanced by Swift-UVOT field astrometry, is RA: 06
30 45.52 Dec: -60 31 12.9, with an error radius of 2.1 arcseconds (90%
confidence). This is coincident with the new object not visible in DSS or
2MASS, but recently detected with GROND [ATel #3813]. Swift-UVOT (using the
UVW1 filter; ~2000-3300 Angstrom) also detects this new object at RA: 06 30
45.42 Dec: -60 31 12.54 (error radius 0.44 arcseconds).
The Swift-XRT X-ray spectrum is very soft and can be best fit with a
blackbody of kT = 48 (+/-5) eV, freezing the column density at the Galactic
value in the direction of the source; 5.11 E20 cm^-2. The observed 0.2-2 keV
flux in the Swift-XRT observation is 3.4 (+0.8, -1.2) E-12 ergs/s/cm^2. This
is a reduction in flux from the XMM-Newton Slew observation by a factor of
approximately 12 (in ATel #3811 the flux was incorrectly described as
unabsorbed, when it should have been absorbed). There is essentially no flux
above 2 keV.
The Swift-XRT lightcurve shows no significant variability in flux or
spectral hardness.
The Swift-UVOT lightcurve is suggestive of flux variability, with UVW1
magnitudes between 17.2 and 17.5.
We would like to thank the Swift team for their rapid scheduling of this
follow-up observation.
