GCN Circular 25978

GRB 191004B: Swift/UVOT Detection

S. J. LaPorte (PSU) and S. B. Cenko (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 191004B
69 s after the BAT trigger (Cenko et al., GCN Circ. 25947
Not found
 
 
).
A fading source consistent with the XRT position
(Beardmore et al. GCN Circ. 25951
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  03:16:49.10 =  49.20459 (deg.)
    Dec (J2000) = -39:38:03.9  = -39.63441 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence),
consistent with the positions reported by LCO (Strausbaugh et al. GCN Circ.
25949
Not found
 
 
),
NOT (Heintz et al. GCN Circ. 25954
Not found
 
 
), VLT/X-Shooter (D'Elia et al. GCN Circ.
25956
Not found
 
 
),
COATLI (Watson et al. GCN Circ. 25958
Not found
 
 
), and GROND (Schady et al. GCN Circ.
25960
Not found
 
 
).

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

b                    38697         38997          295           >20.42
uvm2             44827         45727          885           >20.25
u                       294              387            91           >19.04

v                    43916         44822          885           >20.07
uvw1             45734         46281          538            >19.96
uvw2             39915         40544          618            >20.09
white                   82             232          147
18.01+-0.05
white             39003         39909          885              20.51+-0.13



The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).