GCN Circular 7870

D. A. Perley, J. S. Bloom, A. A. Miller, J. Shiode, J. Brewer, D. Starr, 
and R. Kennedy (UC Berkeley) report:

On the night of 2008-06-07 (UT) we re-observed the location of GRB 
080603A (GCN 7790
Not found
 
 
, Paizis et al.) with Keck I / LRIS in g and R filters 
for 785s and 690s respectively, starting at 12:30 UT.  The optical 
afterglow (Gomboc et al., GCN 7788
Not found
 
 
; Chornock et al., GCN 7789
Not found
 
 
) is 
well-detected as the northern member of a complex of sources. 
Calibrating relative to four nearby USNO B1.0 stars we estimate an 
afterglow magnitude of

R = 23.7 +/- 0.1  (t = 4.05 days)

The extended source reported by Rymyantsev et al. (GCN 7860
Not found
 
 
) is clearly 
detected and is well-resolved into the afterglow plus two extended 
sources in the g-band frame, with the southern source significantly 
redder than the afterglow and the faint western source.

A color image of the field is posted to:

http://lyra.berkeley.edu/~dperley/080603a/080603a_color.png

Given the very strong absorption lines reported in our spectroscopic 
observations (Perley et al., GCN 7791
Not found
 
 
), this complex may be a bright 
host galaxy of this burst, as suggested by Rumyantsev et al.  However, 
the sources above are offset significantly from the afterglow (which 
itself is not obviously extended), suggesting instead that they may 
represent one or both of the intervening absorbers.

Later the same night, we acquired 2x900s spectra using a slit covering 
the northern (afterglow) source and southern source, and an additional 
1x600 spectrum using a slit covering the faint western source and the 
bright, clearly separated eastern source noted by Kann et al. (GCN 
7822
Not found
 
 
).  No obvious emission lines are evident in any spectrum.  At any 
of the host and absorber redshifts of z=1.688, z=1.563 and z=1.271 
respectively, the bright potential emission features (Ly-alpha, OII) are 
expected to fall outside our wavelength coverage, on top of sky lines, 
or be strongly attenuated by the atmosphere, so this result is mildly 
supportive of an association of these sources with the host and/or 
absorbers.  However, the integrations were relatively short, and further 
follow-up is warranted.