[vsnet-grb-info 20894] GRB 180720C: Swift/UVOT Upper Limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22992
SUBJECT: GRB 180720C: Swift/UVOT Upper Limits
DATE:    18/07/21 08:35:26 GMT
FROM:    Samantha Oates at MSSL  <sro at mssl.ucl.ac.uk>

S. R. Oates (U. Warwick) and S. J. LaPorte (PSU) report on behalf
of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180720C
100 s after the BAT trigger (LaPorte et al., GCN Circ. 22982).
No optical afterglow consistent with the XRT position (Evans et al., GCN
Circ. 22987) 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)         100         250          147           >20.3
white              100         5490         541           >21.0    
u (FC)             312         425          111           >19.2
u                  312         11199       1193           >20.6
v                  4263        5901         393           >19.1
b                  3646        11902       1072           >20.8
uvw1               4674        10285       1133           >20.3
uvm2               4469        6106         393           >19.7
uvw2               4058        5696         393           >19.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the significant reddening of E(B-V) = 2.11 in the direction of the burst
(Schlegel et al. 1998).