TITLE:   GCN CIRCULAR
NUMBER:  13678
SUBJECT: GRB 120816A: Swift/UVOT Detection of the Optical Afterglow
DATE:    12/08/18 16:32:59 GMT
FROM:    Stefan Immler at NASA/GSFC  <stefan.m.immler@nasa.gov>

S. Immler (NASA/CRESST/GSFC) and K. L. Page (U Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT observed the field of GRB 120815A starting 117 s
after the BAT trigger (Page et al., 2012, GCNC 13654). We detect
an uncatalogued source inside the enhanced XRT error circle
(Osborne et al., 2012, GCNC 13660) with preliminary coordinates

   RA (J2000.0) = 18:48:34.5 = 282.14359 (deg)
  Dec (J2000.0) = -06:56:16.4 = -6.93788 (deg)

and an estimated uncertainty of 0.6 arcsec (radius, 90% confidence,
statistical + systematic). The UVOT detection is consistent with
the optical afterglow reported by Rau et al. (2012, GCNC 13657).
Source magnitudes and 3-sigma upper limits at this location are
given below (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373).

Filter       TSTART   TSTOP    Exp Time      Mag  Err
-----------------------------------------------------
white          134      284         147      18.5  0.2
white          573     6306         598      19.9  0.2
    v          117     6716         500     >19.0
    b          548    11345        1174     >19.6
    u          293     7286         672     >21.1
 uvw1          672     7126         490     >21.1
 uvm2          647     6921         490     >19.5
 uvw2          599     6511         490     >19.8
-----------------------------------------------------

The quoted magnitudes and upper limits have not been corrected for
the Galactic extinction along the line of sight to this burst of
E_{B-V} = 0.703 mag.