[vsnet-grb-info 4487] GRB 070406: Gemini South Imaging and XRT analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6259
SUBJECT: GRB 070406: Gemini South Imaging and XRT analysis 
DATE:    07/04/08 05:05:48 GMT
FROM:    Josh Bloom at UC Berkeley  <jbloom at astron.berkeley.edu>

J. S. Bloom (UC Berkeley), H-W. Chen (Chicago), J. X. Prochaska (UC  
Santa Cruz), N. R. Bulter (UC Berkeley) report:

We observed the field of GRB 070406 (Cummings et al.; GCN 6247) with  
the GMOS instrument on Gemini South in r and i-band filters. An i- 
band finder is provided (*) with mean epoch 7.26 April 2007 UT (~29.4  
hours after the GRB). The images cover the region of the XRT source  
(Troja et al.; GCN 6255). Our re-analysis of the XRT data, based on  
the first 20 ks and allowing for the possiblity of an astrometric XRT  
frame offset, yields a moderately larger XRT error circle (labeled  
"Butler") of:

        RA(J2000) =  13:15:51.16  DEC =  +16:30:47.7  (6.4" at 90%  
confidence)

We cannot confirm any variability of the X-ray source. The SDSS  
galaxy noted by Kann (GCN 6256) and the faint source noted by  
Malesani et al. (GCN 6257) are well detected. We note that the  
Malesani source appears to be resolved and it thus unlikely to be the  
afterglow (it also appears marginally detected in the SDSS i-band  
image from Cool et al. GCN 6248). We note 5 additional sources in the  
XRT error circle (J2000):

                 RA                  DEC
    s1   13:15:51.41  +16:30:42.6
    s2   13:15:51.19  +16:30:41.9
    s3   13:15:50.94  +16:30:42.6
    s4   13:15:50.75  +16:30:48.0
    s5   13:15:51.48  +16:30:52.7

We make no claims about variability at this time.

We find no source at the location of the Xin et al. transient (GCN  
6253). However, we do detect a faint source ~2.3 arcseconds to the  
South West of that position at:

    OT?  13:15:40.91  16:34:13.1

This source is several magnitudes fainter than the galaxy to the  
northwest noted by Xin et al., whereas Xin et al. indicate that their  
source was 4 magnitudes brighter at 35.4 hour after the GRB."

This message can be cited.

(*) http://lyra.berkeley.edu/~jbloom/grb070406_ep1.pdf

GRAASP thanks to Henry Lee and the observing team at Gemini South for  
performing these ToO observations.