GCN Circular 5996
H.-W. Chen (U Chicago), J. Dembicky (APO), D. York, D. Lamb (U Chicago), R. McMillan, B. Ketzeback, and G. Saurage (APO) report on behalf of a larger collaboration: "We obtained 5x600 sec dithered exposures in each of the SDSS i' and z' bands of the field of GRB070103 (Sakamoto et al., GCN 5988), using the SPIcam on the 3.5 m telescope at the Apache Point Observatory. The observations started at Jan 04.05 UT (~ 4.5 hrs after the initial Swift trigger) under photometric conditions with a mean seeing of 1.6-2 arcsec. Calibrating the final stacks based on a SDSS standard field observed through these filters gives 5-sigma depths of AB(i')=24.6 and AB(z')=24.0 over a 2-arcsec diameter aperture at the location of the x-ray source reported by Mangano et al. (GCN 5992). "