GCN Circular 7116

M. De Pasquale, P. Schady (MSSL-UCL) and J. Cummings (GSFC/GWU)
report on behalf of the Swift/UVOT team:

  The Swift/UVOT began observing the field of GRB 071118 (Cummings
et al, GCN 7106
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 ) 123s after the BAT trigger.

  In the v band finding chart, an uncatalogued source is detected
inside the refined XRT error circle (Moretti et al 7111) with ~6
sigma significance. This source looks extended; however it is not
found at late times, which indicates that it is the optical
afterglow of GRB 071118. Its detection suggests that this GRB
took place at redshift z<~5. The coordinates of this source are

  RA:    19 58 51.8
  Dec:  +70 07 29.2

  with an error of 0.6 arcsecond. No new source is detected within
the XRT error circle in the b, u or uv filters, either in the single
or co-added exposures.

  In the table below, we indicate the magnitude of the optical
afterglow and the 3sigma upper limits. We do caution that the
photometry may be affected by the halo of a near bright star and
the crowded field.

  Filter   Time (s)  Exp time (s)        Mag

  White    134-233      98            > 20.6

  White    734-743      9.8           > 19.4

  White    874-973      98          20.4 +/- 0.2

  White  1484-1983      39            > 20.6

  White  5756-7391     393            > 21.4


   v       240-639     393          19.1 +/- 0.2

   v       774-793     9.8            > 18.1

   v      981-1380     393          19.1 +/- 0.2

   v     1524-2033      78            > 19.1

   v     6166-7801     198            > 19.2

   v   17862-18769     885            > 20.4


   b      720-1696      87            >20.0

   b     5551-7186     393            >20.6


   u      695-2093     122            >20.0

   u    5345-13654    1096            >21.0


  w1      670-2083     136            >19.9

  w1     6576-6775    1078            >21.2


  um2     646-2058     136            >20.4

  um2   11126-18883   1250            >21.2


  uw2     750-2009      98            >19.7

  uw2   6371-18883     750            >21.1


  No correction has been made for the expected high
Galactic extinction, corresponding to E(B-V) of 0.37.