TITLE: GCN CIRCULAR NUMBER: 7870 SUBJECT: GRB 080603A: Late-time Keck imaging and spectroscopy DATE: 08/06/13 00:28:58 GMT FROM: Daniel Perley at U.C. Berkeley 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, 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; Chornock et al., GCN 7789) 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) 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), 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). 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.