GCN Circular 30572
Subject
GRB 210731A: Swift/UVOT Detection of an optical afterglow
Date
2021-08-01T14:44:28Z (3 years ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
N. P. M. Kuin (UCL-MSSL) 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 210731A
210 s after the BAT trigger (Troja et al., GCN Circ. 30568).
An optical afterglow consistent with the XRT position (D'Ai et al.
GCN Circ. 30569) and discovered by Meerlicht (de Wet ert al, GCN Circ.
30570) is also detected in the initial UVOT exposures. Interestingly, the
initial rise to peak is slow.
Preliminary 3-sigma magnitudes using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures
are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 210 273 62 20.2 +/- 0.38
b 17547 18204 587 19.02 +/- 0.08
u 29863 30504 624 18.66 +/- 0.09
v 11787 12145 348 18.60 +/- 0.17
uvw1 28956 29857 886 19.33 +/- 0.14
uvw2 34767 35667 886 20.41 +/- 0.27
uvm2 23308 23846 530 19.40 +/- 0.21
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.092 in the direction of the burst
(Schlegel et al. 1998).