[vsnet-grb-info 27594] GRB 210321A: Swift/UVOT Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29697
SUBJECT: GRB 210321A: Swift/UVOT Detection
DATE:    21/03/23 14:17:59 GMT
FROM:    Sam LaPorte at PSU  <sjl5346 at psu.edu>

 GRB 210321A: Swift/UVOT Detection

S. J. Laporte (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
(Beardmore et al. GCN Circ. 29681)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  05:51:34.75 =  87.89479 (deg.)
    Dec (J2000) = +70:07:49.8  =  70.13051 (deg.)
with an estimated uncertainty of 0.49 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits 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         2885          147         18.69 +/- 0.09
v                 2892         4465          331         18.44 +/- 0.16
b                 3713         3913          197         18.64 +/- 0.11
u                 3507         3706          197         18.29 +/- 0.12
w1                3302         3502          197         18.48 +/- 0.17
m2                3097         3296          197        >18.9
w2                4124         4324          197        >19.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.118 in the direction of the burst
(Schlegel et al. 1998).