TITLE:   GCN CIRCULAR
NUMBER:  42191
SUBJECT: GRB251007A: Swift/UVOT Detection
DATE:    25/10/10 17:40:49 GMT
FROM:    Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>

M. H. Siegel (PSU) and E/ Ambrosi (INAF-IASFPA) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 251007A 79 s after the BAT trigger (Ambrosi et al., GCN Circ. 42146). A fading source consistent with the XRT position (Beardmore et al., GCN Circ. 42161) and the previously reported optical source (Wu et al., GCN Circ. 42154; Malesani et al., GCN Circ. 42158, Hu et al. GCN Circ 42174) is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  08:32:42.39 = 128.17664 (deg.)
    Dec (J2000) = +21:48:46.3  =  21.81285 (deg.)
with an estimated uncertainty of 0.45 arc sec. (radius, 90% confidence).

Preliminary detections 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               80          229          146      18.42+/-0.08
white            17739        18156          406            >20.41
v                11939        39105         2335            >20.09
b                16827        17734          885            >20.39
u                  291          418          124      19.11+/-0.36
uvm2             27913        39155          906            >20.29
uvw2             23059        34819         1506            >20.58


The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.039 in the direction of the burst
(Schlegel et al. 1998).