[vsnet-grb-info 27576] GRB 210321A: Swift/UVOT Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29679
SUBJECT: GRB 210321A: Swift/UVOT Detection
DATE:    21/03/21 13:35:49 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <mhs18 at psu.edu>

M.. H. Siegel (PSU) and S. Dichiara (NASA/GSFC/UMCP)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210321A
2735 s after the BAT trigger (Dichiara et al., GCN Circ. 29677).
A source consistent with the XRT position (Perri et al., GCN Circ. 29678)
is detected in the initial UVOT exposures.

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             2735         2837          100         18.76 +/- 0.11

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.116 in the direction of the burst
(Schlegel et al. 1998).