TITLE:   GCN CIRCULAR
NUMBER:  14449
SUBJECT: GRB 130427A: P60 early nondetection
DATE:    13/04/27 08:39:09 GMT
FROM:    Daniel Perley at Caltech  <dperley@astro.caltech.edu>

D. A. Perley (Caltech) reports on behalf of a larger collaboration:

The Palomar 60-inch telescope automatically responded to GRB 130427A 
(Maselli et al., GCN 14448) and began taking observations at 07:52:22 UT 
(4.42 minutes after the BAT trigger).  A series of 60-second images were 
taken in r, i, and z filters; observations are still ongoing. Inspection 
of individual frames shows no detection of an optical transient 
consistent with the XRT position to approximately r > 20.6 mag, i > 20.7 
mag, z > 19.7 mag.

Nondetection of an afterglow in rapidly-triggered P60 observations is 
unusual (Cenko et al. 2009, ApJ 693, 1484), especially in the presence 
of an very bright GRB and early XRT afterglow.  This is suggestive of a 
highly extinguished (or possibly high-redshift) burst, and may indicate 
that the possible UVOT source reported by Maselli et al. was spurious. 
Further observations, especially in the NIR, are strongly encouraged.