TITLE:   GCN CIRCULAR
NUMBER:  6245
SUBJECT: GRB 070311, deep optical photometry
DATE:    07/04/04 19:37:04 GMT
FROM:    Peter Garnavich at U of Notre Dame  <pgarnavi@nd.edu>

P. Garnavich (Notre Dame), X. Dai,  R. Pogge (Ohio State),
J. Hill (LBTO/UAz), X. Fan (U Ariz), J. Prieto, K. Z. Stanek (Ohio State),
R. M. Wagner (LBTO/OSU), J. Rhoads (Ariz State), E. Egami, J. Bechtold,
S. Herbert-Fort (U Ariz) report:

The Large Binocular Telescope (LBT) imaged the position of the GRB 070311
afterglow (Mereghetti et al, GCN 6189; Covino et al. GCN 6190;
Dai et al. GCN 6219) with the LBC-blue CCD camera
(http//lbc.mporzio.astro.it) and 8.4-m SX mirror on 2007 March 20.13 (UT).
Fifteen dithered, 200 second exposures were obtained with the
Sloan-r filter in 0.8" seeing. After combining the images, the
afterglow is still clearly detected. Using the same calibration as
Dai et al. (GCN 6219), we estimate the brightness of the afterglow
to be R2=25.42+/-0.12 mag at 9.0 days after the burst.

The new LBT image shows evidence of a faint host galaxy 1.8" to
the west of the GRB afterglow. After subtracting the afterglow
using DAOPHOT (Stetson 1987, PASP, 99, 191) we estimate the host
brightness at R2=25.5+/-0.2 mag in a 1.1" radius aperture.

The LBT photometry 9 days after the burst shows a continued
decay from the optical flare, but the rate of fading is not as
steep. The afterglow may be approaching a more typical
post-break decay index. The light curve of 070311 is available at:
http://www.astronomy.ohio-state.edu/~xinyu/grb/070311.jpg
and uses photometry from GCNs 6198 (Wren et al. 2007), 6195
(Halpern & Armstrong 2007), 6199 (Halpern & Armstrong 2007), 6203 (Halpern
& Armstrong 2007), 6204 (Greco et al. 2007), 6206 (Kann et al. 2007), 6208
(Halpern & Armstrong 2007), 6219 (Dai et al. 2007).


The LBT is an international collaboration among institutions in the
United States, Italy and Germany. The LBT Corporation partners are:
*  The University of Arizona on behalf of the Arizona university system
*  Istituto Nazionale di Astrofisica, Italy
*  LBT Beteiligungsgesellschaft, Germany, representing the Max Planck
Society, the Astrophysical Institute Potsdam, and Heidelberg University
*  The Ohio State University
*  The Research Corporation, on behalf of The University of Notre Dame,
University of Minnesota and University of Virginia


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