[vsnet-grb-info 26242] GRB 200901A: Swift/UVOT Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28342
SUBJECT: GRB 200901A: Swift/UVOT Detection
DATE:    20/09/01 20:16:07 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld at ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and K. K. Simpson (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 200901A 3053 s after the BAT trigger 
(Simpson et al., GCN Circ. 28335).
A possible optical afterglow consistent with the XRT position (Kennea et al., GCN Circ. 28341) is 
detected in the initial UVOT exposures in the white filter only. It is not clear whether the source 
is fading.
Preliminary detections and 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          3053         3202          147         20.6 +/- 0.3
white             3916         4115          197         20.5 +/- 0.2
v                 4326         4526          197         >19.1
b                 3711         3910          197         >20.4
u                 3211         4987          290         >20.0
w1                4736         4936          197         >19.1
m2                4531         4731          197         >19.1
w2                4121         4321          197         >19.3

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of 
E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).