GCN Circular 29630

GRB 210308A: Swift/UVOT Detection

J. D. Gropp (PSU) and V. D'Elia (SSDC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210308A
95 s after the BAT trigger (D'Elia et al., GCN Circ. 29619
Not found
 
 
).
A source consistent with the XRT position
(D'Elia et al., GCN Circ. 29619
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  04:28:17.73 =  67.07389 (deg.)
    Dec (J2000) = +37:26:02.1  =  37.43391 (deg.)
with an estimated uncertainty of 0.46 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

b                       765            1189            38        >18.62
uvm2                864            1115            38        >17.52
u                       338            1164          284        >19.50
v                       667            1090            58        >17.84
uvw1               1120            1140            19        >17.25
uvw2                 815            1231            50        >17.91
white                 126             275           292
18.54+-0.07
white                 618            1213          205        >20.20

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.296 in the direction of the burst
(Schlegel et al. 1998).