[vsnet-grb-info 17910] GRB 160425A: Swift/UVOT Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19357
SUBJECT: GRB 160425A: Swift/UVOT Detection
DATE:    16/04/27 20:10:02 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <siegel at swift.psu.edu>

M. H. Siegel (PSU) and H. A. Krimm (CRESST/GSFC/USRA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160425A
208 s after the BAT trigger (Krimm et al., GCN Circ. 19343).
A fading source consistent with the XRT position (Beardmore et al. GCN Circ. 19347)
is detected in the initial UVOT exposures.  This source is consistent
with the optical transient reported by MASTER (Lipunov et al, GCN Circ. 19344)
and  GROND (Bodensteiner et al., GCN Circ. 19349). The source has plateaud over
the last day, which may indicate detection of the host galaxy reported
by MASTER (Balanutsa et al., GCN Circ. 19351).

The preliminary UVOT position is:
   RA  (J2000) =  18:41:18.58 = 280.32743 (deg.)
   Dec (J2000) = -54:21:36.3  = -54.36007 (deg.)
with an estimated uncertainty of 0.53 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits 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)         208          358          147         19.57 +/- 0.10
white              859         1009          147         20.70 +/- 0.35
white             1164         2397          155        >20.19
white             6727         8221          254        >20.79
white            11858        12765          885         21.03 +/- 0.19
white            35282        41433         2162         21.48 +/- 0.23
white            46310        58620         3898         21.48 +/- 0.16
white           104099       111153         2061         21.80 +/- 0.30
v                  365         2447          233         19.22 +/- 0.31
b                  465         1852          156         20.16 +/- 0.32
u                  440         6517          410         20.07 +/- 0.26
w1                 415         7748          607         20.24 +/- 0.30
m2                 390         7542          430        >19.7
w2                 515        13672         1296        >20.8

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 burst
(Schlegel et al. 1998).