TITLE:   GCN CIRCULAR
NUMBER:  28827
SUBJECT: GRB 201104B: Swift/UVOT Detection
DATE:    20/11/04 20:16:09 GMT
FROM:    Frank Marshall at Swift/UVOT  <marshall@milkyway.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC), S. R. Oates (U.Warwick) and B. Sbarufatti (PSU)

report on behalf of the Swift/UVOT team:



The Swift/UVOT began settled observations of the field of GRB 201104B

56 s after the BAT trigger (Sbarufatti et al., GCN Circ. 28825).

A source consistent with the XRT position

(Sbarufatti et al. GCN Circ. 28825)

is detected in the initial UVOT exposures.



The preliminary UVOT position is:

    RA  (J2000) =  00:20:51.65 =   5.21520 (deg.)

    Dec (J2000) = +07:50:29.4  =   7.84150 (deg.)

with an estimated uncertainty of 0.43 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               56          206          147         18.63 +/- 0.06

u                  268          459          188         19.45 +/- 0.23



The magnitudes in the table are not corrected for the Galactic extinction

due to the reddening of E(B-V) = 0.045 in the direction of the burst

(Schlegel et al. 1998).