TITLE: GCN CIRCULAR NUMBER: 13267 SUBJECT: GRB 120422A: Additional Gemini observations and Keck/LRIS spectroscopy DATE: 12/04/27 16:45:33 GMT FROM: Daniel Perley at Caltech D. A. Perley (Caltech), A. Cucchiara (UCO/Lick), S. B. Cenko (UC Berkeley), A. J. Levan (Warwick), S. R. Kulkarni, S. Ben-Ami, and Y. Cao (Caltech) report: We conducted a second epoch of imaging at the position of GRB 120422A (Troja et al., GCN 13243) with GMOS-N on Gemini-North starting at 05:42 UT on 2012-04-26 in each of the griz filters. Seeing conditions were excellent (0.7"), cleanly resolving the transient previously identified by Cucchiara et al. (GCN 12345) from its putative host galaxy. A curved bridge of emission connects the transient with the host, suggesting it occurred either in a spiral arm (however no counter-arm is visible on the far side of the galaxy) or within an interacting companion. An image is posted to: http://www.astro.caltech.edu/~dperley/gcn/120422a/120422a_gmos.png The transient has clearly faded since the last observations, and is now at r = 22.05 +/- 0.09 mag, i = 22.31 +/- 0.07 mag (using a 0.7" radius aperture and calibrating relative to SDSS standards, with the uncertainties due almost entirely to the systematics of the color comparison). This would indicate a relatively blue color. However, the (nearly contemporaneous) g-band flux lies approximately 1 magnitude below a simple extrapolation of the r-i color, indicating that the SED peaks in or near the r-band range. As previously noted by Schulze et al. (GCN 13257) on the basis of the blue UVOT color, this type of SED is very unusual for traditional GRB afterglows (which normally are power-laws in the optical band) but similar properties have been seen at early times in GRBs 060218 (e.g. Campana et al., Nature 442:1008), as well as GRBs 100316D (Starling et al. 2011, MNRAS 411:2792), and 101225 (Thöne et al. 2011, Nature 480:72). We suggest that the apparent color evolution of the peak wavelength of the transient from the UV to the optical and NIR is likely to continue in subsequent days, and encourage multi-band photometric follow-up as well as spectroscopy. Additionally, on the night of 2012-04-27 UT we acquired 30 minutes of spectroscopy using LRIS on the Keck 10m telescope. A preliminary flux calibration of the spectrum shows a similar signature as evident in the photometry, with a pronounced, smooth peak around 6500 Angstroms. No obvious absorption or emission features are evident except for the narrow emission lines from the underlying host, previously mentioned by Tanvir et al. (GCN 13251) and Schulze et al. (GCN 13257). In particular, we do not yet recognize any broad supernova signatures. Further observations are planned.