TITLE:   GCN CIRCULAR
NUMBER:  42007
SUBJECT: GRB 250925A: Swift/UVOT Upper Limits
DATE:    25/09/26 16:33:59 GMT
FROM:    noelklin@umbc.edu

N. J. Klingler (NASA-GSFC/UMBC/CRESST II) reports on behalf of the
Swift-UVOT team:

Swift-UVOT has performed follow-up observations of the Swift-BAT-detected burst GRB 250925A (Dichiara et al. GCN 41985), collecting 6.0 ks of observations between T0+3.74 ks and T0+16.74 ks.  No source was detected in the UVOT data at the position of the optical source detected by the Nordic Optical Telescope (NOT) reported by Corcoran et al. (GCN 41990; RA, Dec = 22 44 51.31, +46 33 21.3), which is also consistent with the enhanced position of the X-ray source detected by Swift-XRT reported by Page et al. (GCN 41988; RA, Dec = 22 44 51.30, +46 33 20.6).

3-sigma upper limits (AB) using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are:

Filter 		T_start(s) 	T_stop(s) 	Exp(s) 		Mag
white		4150.3 		4350.1 		199.80    	>21.55
white 		9527.3 		10434.5 	907.20    	>22.41
B 		3945.3 		5554.0 		1608.70    	>21.16
U 		3739.8 		3939.6		199.80    	>20.48
U 		5175.9 		5375.7 		199.80    	>20.52
V 		4560.9 		4760.7 		199.80    	>19.94
V 		15320.0 	16227.1 	907.10    	>20.81
W1 		4971.0 		5170.7 		199.70    	>20.10
W2 		4356.1 		4555.9 		199.80    	>20.10
W2 		10440.9     	11158.4 	717.50    	>21.02
M2 		4765.8 		4965.6 		199.80    	>19.99
M2 		16232.4 	16737.3 	504.90    	>20.67

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.254 in the direction of the burst (Schlegel et al. 1998).