GCN Circular 12087
Subject
Swift J185003.2-005627: Swift-XRT/UVOT refined analysis
Date
2011-06-25T16:51:02Z (14 years ago)
From
Andy Beardmore at U Leicester <apb@star.le.ac.uk>
A. P. Beardmore (U. Leicester), S. Campana (INAF-OAB), J. A. Kennea
(PSU) and C. A. Swenson (PSU) report on behalf of the Swift/XRT
and UVOT teams:
We have analysed 2.8 ks of Swift/XRT data from the transient Swift
J185003.2-005627 (Beardmore, et al., GCN Circ. 12083), from 88 s to
17.5 ks after the BAT trigger. The data comprise 421 s in Windowed
Timing (WT) mode (the first 5 s were taken while Swift was slewing),
with the remainder in Photon Counting (PC) mode.
The astrometrically corrected X-ray position for this source (using
the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue), derived from 1660 s of XRT Photon Counting mode data and 2
UVOT images, is RA, Dec = 282.51390, -0.93980 which is equivalent to:
RA (J2000): 18 50 3.33
Dec (J2000): -00 56 23.3
with an uncertainty of 1.7 arcsec (radius, 90% confidence). This
position may be improved as more data are received. The position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and
Evans et al. (2009, MNRAS, 397, 1177).
The X-ray light curve initially decays like a powerlaw, with an index
of 1.158 (+0.102, -0.125), before flattening to a slope of 0.161
(+0.035, -0.072) at T +365 (+109, -40) s after the trigger.
A spectrum formed from the WT mode data from T+101 to T+429 s after
the trigger is best fit by an absorbed blackbody, with a temperature
of 0.83 +/- 0.03 keV and column density of 1.71 +/- 0.19 x 10^22
cm^-2, consistent with the Galactic column in the direction of the
source (Kalberla et al. 2005). The observed (unabsorbed) 0.3-10 keV
flux for this spectrum is 4.85e-10 (6.76e-10) ergs cm^-2 s^-1.
The XRT spectrum, together with the soft BAT spectrum reported by
Markwardt et al. (GCN Circ. 12086) and the location of the source in
the Galactic plane, is suggestive of emission from a type I burst.
Swift/UVOT observations of the field were also performed but no
optical counterpart is detected at the XRT position. Preliminary
3-sigma upper limits, using the UVOT photometric system (Poole et
al. 2008, MNRAS, 383, 627), are:
Filter T_start(s) T_stop(s) Exp(s) Mag
---------------------------------------------------------------------------
white 104 5305 628 >18.9
v 593 1763 136 >17.2
b 519 1863 136 >18.9
u 263 1837 382 >19.9
w1 642 1813 130 >19.7
w2 742 5340 125 >20.3
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 16.09 in the direction of the transient
(Schlegel et al. 1998).