TITLE:   GCN CIRCULAR
NUMBER:  7475
SUBJECT: GRB 080319C: KAIT OA observations
DATE:    08/03/20 05:43:41 GMT
FROM:    Weidong Li at UC Berkeley KAIT/LOSS  <weidong@astron.berkeley.edu>

W. Li and A. V. Filippenko, University of California, Berkeley,
report on behalf of the KAIT GRB team:

We have analyzed the KAIT observations of the optical afterglow (OA) of GRB
080319C (GCN 7442, GCN 7460) as reported in GCN 7441. Our first 5 s unfiltered
observation started at 12:27:11 UT, 75 s after the BAT trigger. Four subsequent
5 s exposures from t = 81 s to 100 s indicate a smoothly decaying behavior (but
perhaps not power law). After reaching a minimum at t = 180 s (or perhaps a bit
earlier), the OA brightened steeply to a second prominent peak centered at t ~
320 s, after which the OA decayed as an approximate power law, with evidence
for a gradually steepening decay index. Selected photometry, all unfiltered but
calibrated to the R band via USNO B1:

  t_start (s) exp (s)    mag  mag_err

          75    5.0      17.353 0.057 
         100    5.0      17.71  0.062 
         180   20.0      17.95  0.051
         271   20.0      17.322 0.022
         362   20.0      17.32  0.023 
         453   20.0      17.487 0.027
         845   20.0      18.06  0.048 
        1429   20.0      18.866 0.096