TITLE:   GCN CIRCULAR
NUMBER:  6650
SUBJECT: Swift/UVOT observations of GRB070721B optical afterglow.
DATE:    07/07/21 21:37:28 GMT
FROM:    Massimiliano de Pasquale at MSSL-UCL  <mdp@mssl.ucl.ac.uk>

  M. De Pasquale and H. Ziaeepour (MSSL/UCL) report on the
behalf of the Swift/UVOT:

  The optical afterglow of GRB070721B (Ziaeepour et al. GCN 6640, Schady
et al. 6641) is detected by Swift/UVOT in White filter and V filter
finding chart exposures, taken 100s-200s and 207-607s after the BAT
trigger. It is not detected at 3sigma level in other exposures, either
single or summed ones in all filters, till ~7000s after the trigger.

  In the following table, we report the magnitudes of the afterglow for
the exposures where the source is detected with at least 3sigma level,
and 3sigma upper limits otherwise.


  Filter  Time(s)   Exp(s)      Magnitude

  White   100-200      99       16.82 +/- 0.1

  White   701-711      10        >18.8

  White   855-955      99        >19.9

  White   5089-6716   393        >20.9


   V      207-453     399       16.7 +/- 0.1

   V      621-641      19        >17.5

   V      961-1116    154        >18.3

   V     5500-5699    199        >18.7


   B       687-850     19        >18.4

   B     4884-6519    393        >20.4


   U       662-835     39        >18.5

   U     4679-6314    393        >20.1


  UW1     638-658      39        >18.8

  UW1    638-6109     432        >20.2


  UM2     613-786      39        >18.9

  UM2    613-5904     432        >20.6


  UW2     780-800      19        >18.8

  UW2    780-6902     385        >20.3


  These values are not corrected for the Galactic
reddening towards the bursts E(B-V)=0.02 mag (Schlegel,
Finkbeiner & Davic, 1998)