TITLE: GCN CIRCULAR NUMBER: 7007 SUBJECT: GRB071021: MARGE Optical Limits DATE: 07/10/26 15:23:36 GMT FROM: Heather Swan at U.of Michigan/ROTSE H. Swan (U Mich), I. Smith (Rice), C. Akerlof (U Mich), E. Rykoff (UCSB) and M. Skinner (Boeing) report on behalf of the MARGE collaboration: The AEOS Burst Camera (ABC) on the AEOS telescope, located at the Maui Space Surveillance System on Haleakala, observed the field of GRB071021 (Swift trigger 294974 (T. Sakamoto et al, GCN 6958)). The images are unfiltered 10s exposures that started ~10 minutes after the trigger and ended ~ 2 hour later. We calibrated our images to the USNO-B1 R2 catalog. We do not see the NIR counterpart observed by A. J. Castro-Tirado et al. (GCN 6968), down to the following limiting magnitudes. We have not corrected for the galactic extinction, which is E(B-V)= 0.074 mag, according to the NED Extinction calculator. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 09:51:24.7 09:57:32.2 367.5 22.6 591.7 Y 09:51:24.7 12:09:06.9 8262.3 23.7 591.7 Y The ABC is an unfiltered camera, with enhanced sensitivity in the red end of the spectrum. This sensitivity to the red end of the spectrum allows us to see high (z < 6) bursts. The relatively deep upper limits we have obtained may assist efforts to better determine the redshift for this unusual event.