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GCN Circular 41728

Subject

GRB 250905A: Swift/UVOT Upper Limits

Event

GRB 250905A

Date

2025-09-05T20:04:34Z (4 days ago)

From

Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>

Via

S. R. Oates (Lancaster Uni.) and R. Brivio (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 250905A
140 s after the BAT trigger (Brivio et al., GCN Circ. 41714Loading...
 
 ).
No optical afterglow consistent with the XRT position
(Osborne et al., GCN Circ. 41722Loading...
 
 )
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/3sigUL
white  (FC)     140          290             147           >21.0
   u    (FC)     300           405            103            >19.8
   v              4973       16058          1082            >20.3
   b              5794         5978            181            >20.3
   u              5588       27905          1036            >21.1
uvw1          5383       27038           1082           >20.4
uvm2          5178       16867            989            >20.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.054 in the direction of the burst
(Schlegel et al. 1998).