TITLE:   GCN CIRCULAR
NUMBER:  39968
SUBJECT: GRB 250328A: Swift/UVOT Detection
DATE:    25/03/31 10:23:48 GMT
FROM:    noelklin@umbc.edu

N. Klingler (NASA-GSFC / UMBC / CRESST II), M.H. Siegel (PSU), and P.A. Evans (U. Leicester), report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 250328A 3254 s after the SVOM trigger sb25032803 (GCN Circ. 39910).  A source consistent with the XRT position (Evans et al., GCN Circ. 39967) is detected in the initial UVOT exposures and appears to be fading.

Preliminary detections and 3-sigma upper limits for the early exposures are:

Filter		T_start(s)	T_stop(s)	Exp(s)		Mag(AB)
u		3254		4993		1711		21.93 +/- 0.30
u		8758		8994		232		>21.01
u		177580		190264		970		>21.88

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.018 in the direction of the burst (Schlegel et al. 1998).

This is an official data product of the Swift/UVOT team.