[vsnet-grb-info 5064] GRB 070810b: Image Subtraction of Multiple Keck Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6771
SUBJECT: GRB 070810b: Image Subtraction of Multiple Keck Observations
DATE:    07/09/01 04:05:55 GMT
FROM:    Daniel Kocevski at UC Berkeley  <kocevski at berkeley.edu>

D. Kocevski, J.S. Bloom, C. C. Thoene, and J. Prochaska report:

We performed image subtraction between multiple R-band observations  
of the error box of short burst GRB070810b (Marshall et al., GCN  
6743) with the Keck I telescope (+LRIS).  The first epoch of  
observations began at (UT)  2007-08-11 14:45:00 followed by a second  
epoch six nights later at (UT) 2007-08-17 12:02:00, with equivalent  
exposures of 630 and 900 seconds respectively.  Image subtraction  
using the public POIS-IPP package(*) software shows no variable  
sources associated with the S1, S2 XRT positions (GCN 6754 , Starling  
et al.) or the S3 position (Thoene et al., GCN 6756) nor any  
significant residual sources within the BAT error circle down to a  
limiting magnitude of ~25.5 mag in R band.  The potential candidate  
afterglow close to S2, reported by Pozanenko et al. can be resolved  
as two objects in our images, which show no sign of variability  
between the two epochs.

* See http://pan-starrs.ifa.hawaii.edu/project/IPP/software/