[vsnet-grb-info 14005] GRB 131004A: MOSFIRE NIR imaging

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15319
SUBJECT: GRB 131004A: MOSFIRE NIR imaging
DATE:    13/10/08 09:31:30 GMT
FROM:    Daniel Perley at Caltech  <dperley at astro.caltech.edu>

D. A. Perley (Caltech) reports:

I imaged the location of GRB 131004A (GCN 15303) in Ks-band with MOSFIRE 
on the Keck I telescope on the night of 2013-10-07 for a total 
integration time of 291 seconds under good seeing conditions but some 
cloud cover.  The midpoint of the integration was 07:21 UT, 2.40 days 
after the GRB.

At the location of the optical transient reported by Xu et al. (GCN 
15304), no source is detected to a limiting magnitude of Ks > 20.6.  The 
nearest detected object to this location is a faint (Ks = 19.7), compact 
source approximately 1.4 arcsec to the west, at RA=19:44:26.99, 
dec=-02:57:30.15.

Given the moderate redshift of z=0.717 (Chornock et al., GCN 15307), 
these results suggest either that the host of this event is a relatively 
low-mass galaxy or that the GRB exploded outside the bulk of the stellar 
light of its host.  The >1.5 sec duration and significant lag reported 
in the BAT refined analysis (Lien et al., GCN 15316) may suggest the 
former interpretation is more likely.

I thank D. Malesani for providing the NOT image to verity the location 
of the optical transient.