TITLE:   GCN CIRCULAR
NUMBER:  13901
SUBJECT: GRB 121024A: Swift/UVOT Observations
DATE:    12/10/25 20:02:12 GMT
FROM:    Stephen Holland at STScI  <sholland@stsci.edu>

S. T. Holland (STScI) and C. Pagani (U Leicester)
report on behalf of the Swift/UVOT team:

     The Swift/UVOT began settled observations of the field of GRB
121024A starting 158 s after the BAT trigger (Pagani et al., 2012,
GCNC 13886).  We continued to detect the optical afterglow until
approximately 10 ks after the BAT trigger.  Preliminary UVOT
photometry, and 3-sigma upper limits, for the afterglow is presented
below.

-----------------------------------------------------
Filter       TSTART   TSTOP   Exp Time       Mag  Err
-----------------------------------------------------
    u (fc)     158      408        246     18.43 0.10
-----------------------------------------------------
    v          464      483         19    >18.1
    b          413      433         19     18.44 0.25
    u          538      557         19    >18.5
 uvw1          513      533         19    >18.1
 uvm2          488      508         19    >17.6
 uvw2          439      459         19    >18.1
-----------------------------------------------------

    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} = 0.09 mag (Schlafly et al. 2011, ApJS, 737, 103).  The
photometry is in the UVOT photometric system (Breeveld et al. 2011,
AIP Conf. Proc. 1358, 373).