TITLE:   GCN CIRCULAR
NUMBER:  14456
SUBJECT: GRB 130427A: Continued P60 follow-up of an extremely bright optical afterglow
DATE:    13/04/27 11:52:44 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko@srl.caltech.edu>

D. A. Perley (Caltech) and S. B. Cenko (UC Berkeley) report:

We have continued observations of the afterglow of GRB130427A (Maselli et
al., GCN 14448) with the Palomar 60-inch telescope until the field set.
Relative to SDSS reference stars in the field, in some select recent
images we estimate afterglow magnitudes of:

r' = 14.86 mag  (t = 1.40 hours)
r' = 15.32 mag  (t = 2.31 hours)
r' = 15.55 mag  (t = 3.10 hours)

This is brighter (by about 1 mag) than any other Swift burst as measured
at similar epoch (as of 2010; Kann et al. ApJ 720:1513), though still
significantly fainter than GRB 030329 which reached approximately 13 mag
at 0.1 day.  The rate of fading corresponds to a relatively shallow decay
index of approximately alpha~-0.85, suggesting that this afterglow will
remain bright for an extended period.  Worldwide small-telescope follow-up
(including by amateurs) is strongly encouraged.