GCN Circular 30278

N. P. M. Kuin (UCL-MSSL) and P. D'Avanzo (INAF-OAB) report
on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210619B
136 s after the BAT trigger (D'Avanzo et al., GCN Circ. 30261
Not found
 
 
).
A source consistent with the XRT position (Beardmore et al., GCN Circ.
30267
Not found
 
 
)
was detected in the initial UVOT exposures consistent with the reported
afterglow by Lipunov et al. (GCN Circ. 30259
Not found
 
 
), Jelinek et al. (GCN Circ.
30263
Not found
 
 
),
Kong (GCN Circ. 30265
Not found
 
 
), Kellegrin et al. (GCN Circ. 30268
Not found
 
 
), and Zheng &
Filippenko (GCN Circ. 30273
Not found
 
 
). A redshift measurement of z=1.937 was
reported
by de Ugarte Postigo et al. (GCN Circ. 20272
Not found
 
 
) which puts the Lyman break
right at the center of the UVOT uvm2 filter.

The preliminary UVOT position is:
    RA  (J2000) =  21:18:52.38 = 319.71825 (deg.)
    Dec (J2000) = +33:51:01.6  =  33.85044 (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              136          285          147         14.67 +/- 0.02
white              794          814           19         16.66 +/- 0.06
v                  679          699           19         15.59 +/- 0.10
b                  604          624           20         16.39 +/- 0.08
u                  348          598          246         15.60 +/- 0.03
w1                 729         1107           39         17.22 +/- 0.19
m2                 704         1776          117        >19.3
w2                 655         1726          136         19.20 +/- 0.31

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.173 in the direction of the burst
(Schlegel et al. 1998).