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GCN Circular 12157

Subject
GRB 110709B: Swift/UVOT Observations
Date
2011-07-15T12:00:00Z (13 years ago)
From
Stephen Holland at USRA/NASA/GSFC/SSC <Stephen.T.Holland@nasa.gov>
S. T. Holland (CRESST/USRA/GSFC) and
J. R. Cummings (CRESST/UMBC/GSFC)
report on behalf of the Swift/UVOT team:

      The Swift/UVOT observed the field of GRB 110709B starting 70 s
after the BAT trigger (Cummings et al., 2011, GCNC 12122).  Settled
observations started at 91 s.  We do not detect a source at the
UVOT-enhanced XRT position (Beardmore, et al., 2011, GCNC 12136) in
any of the UVOT filters.  Preliminary 3-sigma upper limits for
detecting a source in the finding charts and in the co-added images,
are

Filter       TSTART       TSTOP  EXPOSURE       Mag
---------------------------------------------------
white (FC) &     91 &       241 &     147 &   >21.1
    u (FC) &    303 &       553 &     246 &   >20.5
white (FC) &    858 &      1008 &     147 &   >21.3
---------------------------------------------------
    v     &     633 &    64,817 &    3519 &   >21.5
    b     &     558 &    54,124 &    3664 &   >22.4
    u     &     303 &    59,906 &    4680 &   >22.2
 uvw1     &     682 &    59,264 &    4730 &   >22.2
 uvm2     &    1235 &    58,357 &    3732 &   >22.3
 uvw2     &     782 &    64,122 &    3530 &   >22.4
white     &      91 &    30,997 &    3107 &   >23.0
---------------------------------------------------

     We find weak evidence for variability at the location of the
USNO-B1.0 source 3.5 arcsec WNW of the XRT position at the time of the
second BAT trigger (Barthelmy et al. 2011, GCNC 12124).  Preliminary
photometry is

Filter       TSTART       TSTOP  EXPOSURE       Mag   Err  Sigma
----------------------------------------------------------------
white &          91 &       241 &     147 &   >21.1   3-sigma UL
white &         583 &       776 &      39 &    20.08 0.35    3.3
white &         858 &      1008 &     147 &   >21.3   3-sigma UL
white &        1161 &      2047 &     117 &    20.96 0.36    3.1
white &        6245 &      6444 &     197 &   >21.4   3-sigma UL
white &        7679 &    11,397 &     340 &    21.07 0.37    3.1
white &       11401 &    12,005 &     590 &   >21.9   3-sigma UL
white &       17893 &    18,800 &     885 &    20.98 0.16    7.8
white &       30335 &    30,997 &     644 &    21.39 0.23    5.2
----------------------------------------------------------------

We note that both the USNO-B1.0 source and the XRT position are
located in the coincidence loss halo of a bright star, which makes
precision photometry difficult.  It is not clear if the apparent
variability seen at the location of the USNO-B1.0 source is real or
not.

     The quoted magnitudes and upper limits have not been corrected
for the large, but uncertain, Galactic extinction along the line of
sight to this burst (E_{B-V} = 0.05 mag, Schlegel et al. 1998, ApJS,
500, 525).
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