[vsnet-grb-info 16591] GRB 150523A: Swift/UVOT Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17872
SUBJECT: GRB 150523A: Swift/UVOT Detection
DATE:    15/05/26 17:15:00 GMT
FROM:    Frank Marshall at GSFC  <femarsha at khamseen.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC) and A. Vargas (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150523A
32968 s after the LAT trigger (Bissaldi et al. GCN Circ. 17864).
A source consistent with the XRT position (Beardmore et al. GCN Circ. 17866)
and the optical afterglow position (Dichiara et al. GCN Circ. 17868 and 17869)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  07:41:08.67 = 115.28613 (deg.)
    Dec (J2000) = -45:25:12.4  = -45.42011 (deg.)
with an estimated uncertainty of 0.78 arc sec. (radius, 90% confidence).

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            33590        39627         1150         21.83 +/- 0.24
v                34212        40619         1433        >20.5
u                32968        44748         2077        >20.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.30 in the direction of the burst
(Schlegel et al. 1998).