TITLE:   GCN CIRCULAR
NUMBER:  10508
SUBJECT: GRB 100316B: Swift/UVOT observations
DATE:    10/03/16 19:29:42 GMT
FROM:    Patricia Schady at MSSL/Swift  <msslba@googlemail.com>

S. R. Oates (MSSL-UCL) and W. H. Baumgartner (GSFC/UMBC) report on
behalf of the Swift/UVOT team:

The Swift/UVOT began observerving the field of GRB 100316B 67s
after the BAT trigger (Baumgartner et al., GCN Circ. 10489). We detect the
optical afterglow in the white, v, b, u and marginally in the uvw1 filter.
The refined UVOT position is RA (J2000)= 163.48809, DEC (J2000)=-45.47265,
which is equivalent to:

     RA (J2000) = 10:53:57.141
    Dec (J2000) = -45:28:21.54

with an estimated uncertainty of 0.52 arcsec (radius, 90% confidence).
This position is consistent with the XRT refined position (Beardmore
et al., GCN Circ 10502). The marginal detection in the uvw1 filter is
consistent with
the VLT redshift upper limit (D'Avanzo et al., GCN Circ. 10495).


Preliminary magnitudes and the 3 sigma upper limits are reported below for
individual optical images and summed UV images.

Filter    T_start(s)  T_stop(s)  Exposure      Mag  Err
###########################################################
white     67           216         147         18.36 +/- 0.05
white     857          1007        147         19.15 +/- 0.09
u	  279          528         246         18.44 +/- 0.10
v         1212         1232        19          18.28 +/- 0.46
b         535          555         19          18.97 +/- 0.36
uvw1	  659          1108        58          18.91 +/- 0.36
uvm2      634          1246        66          > 18.59
uvw2      585          1207        78          > 19.13
###########################################################

The above magnitudes are not corrected for the Galactic extinction
corresponding to a non-negligible reddening of E_{B-V} = 0.14 mag
(Schlegel et al.,
1998, ApJS, 500, 525).  The photometry is on the UVOT photometric system
described in Poole et al. (2008, MNRAS, 383,627).