[vsnet-grb-info 4089] GRB 061201: UVOT Observations of a Fading Optical Afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  5898
SUBJECT: GRB 061201: UVOT Observations of a Fading Optical Afterglow
DATE:    06/12/05 14:14:05 GMT
FROM:    Stephen Holland at USRA/NASA/GSFC/SSC  <sholland at milkyway.gsfc.nasa.gov>

S. T. Holland (CRESST/GSFC/USRA) and F. E. Marshall (NASA/GSFC) report
on behalf of the Swift team:

      UVOT observed the field of GRB 061201 during the first 19972 s
after the BAT trigger (Marshall et al., GCN Circ. 5881).  We detect
the source seen by D'Avanzo (2006, GCN Circ. 5884) at the 4.2-sigma
level in the White filter (160-650 nm) and at the 4.5-sigma level in
a coadded image of all the UV filters.  The coordinates of the source
in the White image are:

   RA(J2000)  =  22:08:32.06
   DEC(J2000) = -74:34:47.9

with a 1-sigma error radius of about 0.5 arcsec, consistent with the
VLT source.

      Our magnitudes and 3-sigma upper limits for all the UVOT filters
are:

Filter    Start     Stop   Exposure     Mag  Err Significance
   V         191   12,136     1118      20.8  3-sigma upper limit
   B         669     6197      206      20.9  3-sigma upper limit
   U         645     5992      216      20.7  0.4    2.6
  UVW1       621   17,926      519      20.7  0.5    2.9
          21,392   58,442   11,555      22.9  0.5    2.5
          86,427  160,471   19,972      23.0  3-sigma upper limit
  UVM2      5384   15,948      676      20.5  0.5    2.7
  UVW2       697     6512      122      19.8  0.5    2.5
White        86     6402      304      20.8  0.3    4.2
Comb. UV    621   17,926     1337      20.8  0.4    4.5

The magnitude in the combined UV exposure (coadded UVW1, UVM2, and
UVW2) between 621 sand 17,926 s is 20.8 +/- 0.4, assuming that the
source has equal magnitude in each of these filters.

      Since the source is detected in the UVW2 filter, we estimate an
upper limit to the redshift of about 1.7.