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GCN Circular 1514

GRB020813: VRI Decay Slopes
2002-08-21T03:19:31Z (22 years ago)
Derek Fox at CIT <>
Mike Gladders (Carnegie Observatories) and Pat Hall
(Princeton/Catolica) report: 

"The photometric data reported previously by us yield the following
decay slopes for the OT of GRB020813.  The decay slopes in various
filters implied by the data from August 13UT are:

    I: -0.677+-0.016 (all data August 13UT)
    I: -0.76+-0.03 (only UT>6.5, to match R&V time range)
    R: -0.82+-0.06
    V: -0.75+-0.05

"These data are consistent with the same power law decay in all three
filters in the time interval 6.5<UT<7.5, and are consistent with the
discussion in GCN #1476. Based purely on these data, the two earlier
I-band data points are 0.045+-0.015 magnitudes too faint, implying
that a break in the decay has already occurred by ~4 hours after the
GRB event. This is again consistent with GCN #1476.

"Also, the data yield decay slopes between August 13 and 14 UT of
-0.96+-0.04,-1.02+-0.01,-1.01+-0.02 in I,R and V respectively. These
values lie midway between the early time slope (above, and GCN #1476),
and the later time slope of -1.4+-0.02 (August 13.99 UT to August
16.03 UT, GCN #1500). The slope derived here is nominally inconsistent
with the decay reported in GCN #1491 (-1.44) over a time window
similar to the data reported here.  However, allowing for the
uncertainties of the three data points in GCN #1491 yields a decay
slope of -1.3+-0.30, consistent with the results reported here.

"It thus appears that the decay slope of this OT has continued to
steepen with time, rather than having undergone a simple break."
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