[vsnet-grb-info 17153] GRB 151027A: UVOT Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18502
SUBJECT: GRB 151027A: UVOT Observations
DATE:    15/10/28 01:04:14 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <siegel at swift.psu.edu>

B. G. Balzer (PSU), M. H. Siegel (PSU) and A. Maselli (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 151027A
96 s after the BAT trigger (Maselli et al., GCN Circ. 18478). We confirm
the source initially reported by Maselli et al. (GCN Circ. 18478) and
since observed by numerous ground-based observatories (Zheng and Filippenko,
GCN Circ. 18479; Elenin et al., GCN Circ. 18480; Perley and Cenko, GCN Circ.
18481; Xu et al., GCN Circ. 18485; Yano et al., GCN Circ. 18491; Wren et al.,
GCN Circ. 18495).  We report a position of:

  RA(J2000)  = +18h 09m 57.26s
  Dec(J2000) = +61d 21' 05.4"

The light curve shows complex behavior, with marginal evidence of brightening
after the initial finding chart, then fading with a decay slope of 0.6-0.8 over
the first orbit. The second orbit magnitudes are consistent with no fading
from those measured at the end of the first orbit while the third orbit
shows significant fading.

Preliminary detections 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 (fc)       95        245        147     14.52+-0.02
white           589        609         19     14.44+-0.04
white           762        782         19     14.71+-0.04
white           858       1008        147     14.81+-0.02
white          1161       1354         38     15.07+-0.04
white          1510       1529         19     15.23+-0.04
white          6449       6649        197     15.28+-0.01
white         23966      24662        677     17.14+-0.01
v               639       1579        116     15.12+-0.04
b               564       1505         97     15.37+-0.03
u               308       1479        323     14.00+-0.03
w1              688       1455         77     14.71+-0.05
m2              663       1598         88     14.98+-0.06
w2              615       1555        116     15.12+-0.05

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).