[vsnet-grb-info 27603] GRB 210318A: Swift/UVOT Upper Limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29706
SUBJECT: GRB 210318A: Swift/UVOT Upper Limits
DATE:    21/03/24 11:05:42 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <mhs18 at psu.edu>

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

The Swift/UVOT began settled observations of the field of GRB 210318A
127 s after the BAT trigger (Troja et al., GCN Circ. 29662).
No optical afterglow consistent with the XRT position
(Troja et al. GCN Circ. 29662)
is detected in the initial UVOT exposures.
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           127          277          147         >20.5
u_FC               285          535          246         >19.9
white              127         1188          353         >21.0
v                  614         1064           58         >18.6
b                  541         1163           58         >19.3
u                  285          535          246         >19.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.017 in the direction of the burst
(Schlegel et al. 1998).