[vsnet-grb-info 16946] GRB 150831B: Swift/UVOT Upper Limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18227
SUBJECT: GRB 150831B: Swift/UVOT Upper Limits
DATE:    15/09/01 20:59:18 GMT
FROM:    Frank Marshall at GSFC  <femarsha at khamseen.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150831B
3089 s after the BAT trigger (Marshall et al., GCN Circ. 18215).
No optical afterglow consistent with the refined XRT position
(D'Avanzo et al., GCN Circ. 18222) is detected in the initial UVOT 
exposures. We note that this is a very crowded field.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

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

white_FC          3089         3239          147         >20.6
v                 3246         3445          197         >18.2
b                 8838         9745          885         >20.3
u                 3861         5659          158         >19.4
w1                3656         3856          197         >19.2
m2                3451         3651          197         >20.2

The magnitudes in the table are not corrected for the large
Galactic extinction in the direction of the burst
(Schlegel et al. 1998).