[vsnet-grb-info 27144] GRB 210104A: Swift/UVOT Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29247
SUBJECT: GRB 210104A: Swift/UVOT Detection
DATE:    21/01/04 22:21:25 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld at ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210104A 71 s after the BAT trigger 
(Troja et al., GCN Circ. 29233).
A fading source is detected in all UVOT filters in the initial exposures, at the position given in 
Troja et al., (GCN Circ. 29233), and also seen by others (Xin et al., GCN Circ. 29235; Hosokawa et 
al., GCN Circ. 29237; Kim et al., GCN Circ. 29238; Lipunov et al., GCN Circ. 29239 and Horiuchi et 
al., GCN Circ. 29241).

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_FC            71          221          147         14.61 ± 0.02
white              562          582           20         16.23 ± 0.05
white             1512         1706           39         17.02 ± 0.05

b                  538          558           20         16.59 ± 0.10
u_FC               283          533          246         15.28 ± 0.03
v                  613          632           20         16.36 ± 0.16
uvw1               662          682           20         16.12 ± 0.16
uvm2               637          657           20         16.58 ± 0.25
uvw2               588          608           20         17.09 ± 0.26

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of 
E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).