[vsnet-grb-info 27453] GRB 210218A: Swift/UVOT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29556
SUBJECT: GRB 210218A: Swift/UVOT observations
DATE:    21/02/23 14:49:18 GMT
FROM:    Alexander Belles at PSU/Swift  <aub1461 at psu.edu>

A. Belles (PSU) and B. Sbarufatti (PSU) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210218A
approximately 170 ks after the BAT trigger (B. Sbarufatti et al., GCN 29529)
due to a Moon constraint. No optical afterglow consistent with the XRT
candidate position is detected (Osborne et al., GCN 29542).

Preliminary 3-sigma upper limit using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first exposure
is:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag
wh           170031       188263         1665            >21.65

The magnitude in the table is not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.19 in the direction of the burst
(Schlegel et al. 1998).