[vsnet-grb-info 12333] GRB 120830A: Swift-XRT and UVOT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13709
SUBJECT: GRB 120830A: Swift-XRT and UVOT observations
DATE:    12/08/31 18:43:14 GMT
FROM:    Wayne Baumgartner at GSFC  <wayne at milkyway.gsfc.nasa.gov>

W. H. Baumgartner (GSFC/UMBC), V. D'Elia (ASDC), M. Siegel (PSU),
F. E. Marshall (NASA/GSFC), J. L. Racusin (NASA/GSFC), J. A. Kennea
(PSU), and D. N. Burrows (PSU) report on behalf of the Swift team:

Swift observed the the error circle for the Fermi/LAT and IPN detected
GRB 120831A (Vianello et al., GCN Circ. 13704, Hurley et al. GCN Circ
13705). Two 4 ks XRT observations were taken to cover the IPN error
region, beginning about 60 ks and 72 ks after the burst.  Together
these two XRT observations cover 100% of the IPN error box.

One uncatologed X-ray source is found within the IPN error box at RA,
Dec = 88.501667, -28.701333 which is equivalent to:

RA (J2000): 05h 54m 00.40s
Dec (J2000): -28d 42' 04.8"

with an uncertainty of 8 arcsec (radius, 90% confidence).  The XRT
source has a significance of 2.5 sigma, and the count rate during this
observation in photon counting mode was 2.53e-3 +/- 1.0e-3 cts sec^-1.

The Swift/UVOT began settled observations of the first of the two
fields for GRB 120830A 59804 s after the LAT/IPN trigger.  No data are
available yet for the second field.  A source consistent with the XRT
source is detected in the initial UVOT exposures.  There is no
corresponding source in the USNO-B1.0 catalog.

The preliminary UVOT position is:
     RA  (J2000) =  05:54:00.65 =  88.50270 (deg.)
     Dec (J2000) = -28:42:06.4  = -28.70178 (deg.)
with an estimated uncertainty of 0.55 arc sec. (radius, 90% confidence).

Preliminary results using the UVOT photometric system (Breeveld et
al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag
white            59804        67310         3679         20.42 +/- 0.04

The magnitude in the table is not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.032 in the direction of the burst
(Schlegel et al. 1998).

There is no convincing evidence for UVOT variability of the source.

Further Swift observations are planned to determine whether the source
is fading.