TITLE:   GCN CIRCULAR
NUMBER:  29559
SUBJECT: GRB 210222B: Swift/UVOT Detection
DATE:    21/02/23 18:57:39 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <mhs18@psu.edu>

M. H. Siegel (PSU) and J. D. Gropp (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210222B
101 s after the BAT trigger (Gropp et al., GCN Circ. 29545).
A source consistent with the XRT position (Gropp et al. GCN Circ. 29545)
is detected in the initial UVOT exposures. This source is also consistent
with previously reported optical detections (Hu et al., GCN Circ. 29546; 
Strausbaugh, GCN Circ. 29547; Mong et al., GCN Circ. 29548; Parley, GCN Circ.
29549; Zhu et al., GCN Circ. 29551, Lipunov et al., GCN Circ. 29554). We note
that the lack of detection in the NUV passbands would be consistent with the
redshift of 2.198 reported by Agui Fernandez et al. (GCN Circ. 29552).

The preliminary UVOT position is:
   RA  (J2000) =  10:18:25.43 = 154.60595 (deg.)
   Dec (J2000) = -14:55:55.1  = -14.93198 (deg.)
with an estimated uncertainty of 0.42 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              101          250          147         16.89 +/- 0.03
v                  588          608           19         16.80 +/- 0.17
b                  515          534           20         17.24 +/- 0.12
u                  259          508          246         16.82 +/- 0.04
w1                 639         1793          124        >18.8
m2                 614         1606           78        >20.1
w2                 564         1732          136        >19.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.102 in the direction of the burst
(Schlegel et al. 1998).