[vsnet-grb-info 27333] GRB 210207B: Swift/UVOT Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29436
SUBJECT: GRB 210207B: Swift/UVOT Detection
DATE:    21/02/09 07:45:09 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <mhs18 at psu.edu>

M. H. Siegel (PSU) and A. Y. Lien (GSFC/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210207B
82 s after the BAT trigger (Lien et al., GCN Circ. 29420).
A source consistent with the XRT position
(Lien et al. GCN Circ. 29420) is detected in the initial UVOT exposures,
as reported in the initial circular and confirmed by ARIES (Kumar et al.,
GCN Circ. 29421), KAIT (Zheng & Filippenko, GCN Circ. 29430) and LCO
(Strausbaugh & Cucchiara, GCN Circ. 294311). We note that the lack
of detection in the two bluer NUV passbands is suggestive of a redshift in
the 1.4-1.9 range.

The preliminary UVOT position is:
    RA  (J2000) =  18:02:32.40 = 270.63500 (deg.)
    Dec (J2000) = +53:40:55.8  =  53.68217 (deg.)
with an estimated uncertainty of 0.42 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 (fc)          83          233          147      13.66+/-1.13
white             4081         5717          393      17.91+/-0.04
white            61938        62307          361      21.06+/-0.32
v                 4492         4692          196      17.61+/-0.10
v                 9433        10341          885      18.54+/-0.09
v                56912        74907         1297     >19.84
b                 3876         5512          393      17.95+/-0.05
b                44686        45593          885     >20.99
b                61025        79012         1770      20.79+/-0.18
u (fc)             295          410          113      14.42+/-0.03
u                 5106         5306          196      17.80+/-0.09
u                43773        44680          885      20.47+/-0.26
u                51795        69087          612     >19.80
uvw1              4901         5101          196      18.23+/-0.18
uvw1             11254        11428          171     >18.90
uvw1             39917        40544          616     >19.72
uvw1             50889        68646         1771     >20.53
uvm2              4697         4896          196     >19.12
uvm2             10346        11246          885     >20.23
uvw2              4287         5871          342     >19.39
uvw2             56005        74346         1771     >20.68

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.041 in the direction of the burst
(Schlegel et al. 1998).