[vsnet-grb-info 6043] GRB 080503: No further optical rebrightening

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7680
SUBJECT: GRB 080503: No further optical rebrightening
DATE:    08/05/05 13:15:41 GMT
FROM:    Daniel Perley at U.C. Berkeley  <dperley at astro.berkeley.edu>

D. A. Perley and J. S. Bloom (UC Berkeley) report on behalf of a larger 
collaboration:

Starting at UT 11:32 on the night of 2008-05-05, we began a series of 
additional r-band imaging follow-up observations of the optical 
counterpart associated with GRB 080503 (GCN 7665, Mao et al.), using 
Gemini-North (+GMOS).

The new source (s2) reported in our previous circular (GCN 7678) is 
still present at about the same magnitude.  Using a stack of 9x180s 
images, we present the following measurement of the magnitudes of s1 and s2:

s1: R = 26.33 +/- 0.20
s2: R = 25.46 +/- 0.09

This is consistent (within about 2-sigma) with the previous night's 
measurement and suggests neither additional rebrightening nor dramatic 
fading.  We continue to strongly encourage follow-up with large-aperture 
instruments.


We also issue the following correction to GCN 7678: the data table at 
the bottom (with heading "UT_start exposure filter magnitude") is not 
valid.  This is photometry of s1 based on an older calibration, and 
including a Keck R-band limiting magnitude that will be refined in a 
future circular.  The preceding photometry of s1 and s2 in that circular 
is still valid.

To reiterate, the r-band evolution of the optical counterpart (s2) to 
date, calibrated to USNO B1.0 R-band, is given by:

t(hr)  magnitude
0.98   R > 25.6
1.5    R > 26.5
26.0   R = 25.28 +/- 0.09
47.4   R = 25.46 +/- 0.09

Further observations are ongoing.