TITLE:   GCN CIRCULAR
NUMBER:  37919
SUBJECT: GRB 241025A: Swift/UVOT Detection
DATE:    24/10/28 01:28:28 GMT
FROM:    noelklin@umbc.edu

N. J. Klingler (GSFC/UMBC/CRESTII) and E. Ambrosi (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 241025A
126 s after the BAT trigger (Ambrosi et al., GCN Circ. 37859).
A source consistent with the XRT position (Evans et al.; GCN Circ. 37868) 
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  22:14:36.83 = 333.65346 (deg.)
    Dec (J2000) = +83:34:32.2  =  83.57562 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: 

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white              126          275          147         17.55 +/- 0.04
v                  671         5229          274        >19.4
b                  595         1347           78        >20.2
u                  339         1322          304        >20.5
w1                 722         5483          101        >21.0
m2                5234         5434          197        >20.2
w2                1030         1050           19        >19.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.249 in the direction of the burst
(Schlegel et al. 1998).