GCN Circular 30246

M. H. Siegel (PSU), M. Baer (PSU) and K. L. Page (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210610A
94 s after the BAT trigger (Page et al., GCN Circ. 30160
Not found
 
 
). A fading source consistent
with the XRT position (Goad et al. GCN Circ. 30165
Not found
 
 
) and the previously reported
optical counterpart (Hosokawa et al., GCN. Circ. 30161; Xu et al., GCN. Circ. 30162;
Kumar et al., GCN Circ. 30163
Not found
 
 
; Lipunov et al., GCN. 30166; de Wet et al. GCN Circ.
30168
Not found
 
 
; Horiuchi et al., GCN Circ. 30169
Not found
 
 
; Youdong et al., GCN Circ. 30185
Not found
 
 
; Watson et 
al. GCN Circ. 30191
Not found
 
 
) is detected in the initial UVOT exposures. The lack of detection
in the NUV filters for this bright counterpart is consistent with the redshift of 3.5
reported by Zhu et al. (GCN Circ. 30164
Not found
 
 
) and Dutta et al. (GCN Circ. 30200
Not found
 
 
).

The preliminary UVOT position is:
   RA  (J2000) =  13:37:07.59 = 204.28161 (deg.)
   Dec (J2000) = +14:27:55.0  =  14.46527 (deg.)
with an estimated uncertainty of 0.43 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 (fc)          94          244          147      17.09+/-0.03
white              587          892           68      17.92+/-0.07
v                  636          829           38      16.74+/-0.14
v                 4299         4498          196            >18.92
b                  562          754           38      17.69+/-0.12
b                16163        17070          885      20.57+/-0.23
b                23125        45112         1552            >21.16
u                  307          557          245            >20.02
uvw1               685         4908          216            >19.37
uvm2              4503         4703          196            >19.16
uvw2              4094         4294          196            >19.10

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.032 in the direction of the burst
(Schlegel et al. 1998).