TITLE:   GCN CIRCULAR
NUMBER:  32978
SUBJECT: GRB 221120A: TURBO Optical Upper Limit
DATE:    22/11/23 21:10:38 GMT
FROM:    Robert Strausbaugh at University of Minnesota  <rstrausb@umn.edu>

R. Strausbaugh (UMN), D. Warshofsky (UMN), P. L. Kelly (UMN) report on
behalf of a larger collaboration:

We observed the GRB 221120A (Eyles-Ferris et al., GCN 32955) field with the
Total-Coverage Ultrafast Response to Binary-Mergers Observatory (TURBO)
prototype telescope in St. Paul, Minnesota on November 21, from 01:34 to
01:36 UT (corresponding to 4.08 hours after GRB trigger) in SDSS g-band and
from 02:45 to 02:47 UT (5.25 hours after GRB trigger) in SDSS r-band
filters.

We acquired a series of 5x30s exposures in each band.  We do not detect any
fading uncatalogued sources in the XRT error region in either band, which
is consistent with available optical upper limits (Swain et al., GCN 32956;
Kuin et al., GCN 32958; Gompertz et al., GCN 32966; Odeh et al., GCN 32968;
Querrard et al., GCN 39276).

The following 3-sigma upper limits in AB magnitudes are calculated using
the Pan-STARRS catalog as reference:

g > 16.0

r > 15.4

These magnitudes are not corrected for foreground Galactic extinction.

The TURBO prototype in St. Paul consists of two co-mounted 11-inch
telescopes each with a 6.6 square degree field of view. TURBO will consist
of two arrays of 8 pairs of co-mounted 11-inch telescopes at two dark-sky
sites: Magdalena Ridge Observatory, New Mexico, USA and Skinakas
Observatory, Crete, Greece.