[vsnet-grb-info 4289] GRB 070208: MDM Optical Decay

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6082
SUBJECT: GRB 070208: MDM Optical Decay
DATE:    07/02/08 19:56:55 GMT
FROM:    Jules Halpern at Columbia U.  <jules at astro.columbia.edu>

J. P. Halpern & N. Mirabal (Columbia U.) report on behalf of the
MDM Observatory GRB follow-up team:

"Monitoring of the afterglow of GRB 070208 (GCNs 6077, 6078, 6079)
in the R-band on the MDM 1.3m telescope consisted of a series of
10-minute exposures beginning on Feb. 8 09:25 UT and ending at
13:12 UT, thus spanning the time 0.25-4 hours after the burst.
Partly cloudy conditions, together with bright moonlight,
resulted in images of highly variable quality.  Nevertheless,
we see the fading optical transient within the Swift XRT error
circle (Sato et al., GCN 6074).  In agreement with the GCNs
listed above, we find the OT 3.0" west and 3.3" south of the
center of a galaxy visible on the POSS (Mirabal & Halpern, GCN 6075)
and in pre-burst SDSS images (Cool et al., GCN 6080).

Preliminary magnitudes for the OT, calibrated with respect to
USNO B1.0 magnitudes of nearby stars, are R=20.04+/-0.08 for the
first exposure centered at 09:30 UT, and R=21.5+/-0.2 for a summed
30-minute exposure centered at 12:55 UT.  Some contamination from
the nearby galaxy is possible in this analysis.  Quoted uncertainties
are statistical only.  This corresponds to a mean power-law decay
index of -0.55.

It is not yet clear from this collection of images, both SDSS
and MDM, if the visible galaxy is the host, or if we should wait
to see if a fainter galaxy underlies the OT of this judged long
burst (Markwardt et al., GCN 6081).

Images are posted at http://www.astro.columbia.edu/~jules/grb/070208/

This message may be cited."