[vsnet-grb-info 16260] Trigger 633105 (aka GRB150301C): Swift/UVOT Observations of XRT Counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17541
SUBJECT: Trigger 633105 (aka GRB150301C): Swift/UVOT Observations of XRT Counterpart
DATE:    15/03/04 03:16:06 GMT
FROM:    Lea Hagen at PSU  <lea.zernow.hagen at gmail.com>

L. M. Z. Hagen (PSU) and A. Y. Lien (GSFC/UMBC)
report on behalf of the Swift/UVOT team:


A point source is detected by UVOT that is consistent with the XRT
counterpart and 2.5 arcsec from the XMM-Newton source discussed in
Evans et al. (GCN Circ. 17536).  This source is also seen in archival
DSS imaging.  It is unclear if this is the same object detected by XRT
or a serendipitous source.  Given how crowded the field is, it is also
likely that the UVOT source is comprised of multiple individual sources.
The coordinates of the UVOT source are
   RA(J2000) = 00:45:14.76 = 11.31150
   DEC(J2000) = +41:50:35.2 = 41.84311

Preliminary detections and 3-sigma upper limits using the UVOT
photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373)
for the available exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white              102         4151          369         19.22+-0.13
v                  592         4562          216        >18.53
b                  518         5241           96        >19.08
u                  261         5177          461         18.60+-0.15
uvw1               641        79666         5117         18.64+-0.05
uvm2               617        45953         1237         18.94+-0.13
uvw2               568         4357          216         18.99+-0.27

The magnitudes in the table are not corrected for the Galactic
extinction due to the reddening of E(B-V) = 0.06 in the direction
of the source (Schlegel et al. 1998).

This field has also been observed previously by UVOT as part of a
different observing campaign, primarily in 2013 and 2014. The
stacked images have the following detections:

Filter      Exp(s)        Mag

v            1406     19.04+-0.19
b            1445     19.77+-0.15
u           27521     18.65+-0.03
uvw1        52236     18.57+-0.02
uvm2        58908     18.65+-0.03
uvw2        65719     18.61+-0.02

These indicate possible variability of the source, but further
analysis will be required to confirm this.