TITLE:   GCN CIRCULAR
NUMBER:  26134
SUBJECT: GRB 191031D: MMT Binospec Optical Upper Limit
DATE:    19/11/01 20:39:58 GMT
FROM:    Kerry Paterson at Northwestern  <kerry.paterson@northwestern.edu>

K. Paterson, W. Fong, K. D. Alexander, G. Schroeder, A. Rouco Escorial (Northwestern) report:

“We observed the field of the short-duration GRB 191031D (Fermi-GBM et al., GCN 26111; D'Elia et al., GCN 26112; Mailyan et al., GCN 26118) with Binospec mounted on the 6.5-m MMT on Mount Hopkins, Arizona, starting on 2019 November 1 at 01:44:13 UT, 4.31 hours after the burst. We obtained 15x120-sec of observations in the r-band in 1.05” seeing and clear conditions.

We do not detect any optical source in or around the enhanced XRT position (Osborne et al. GCN 26117).

We obtain a 3-sigma upper limit of r > 23.5 AB mag on the afterglow or any coincident host galaxy, not corrected for Galactic extinction. Photometry is calibrated to the USNO-B1.0 catalog. This limit is consistent with, and slightly deeper than the limit found by Butler et al. (GCN 26121). We note that the closest, clearly-extended source is 5.48 arcsec to the southwest.

Further observations are planned. We thank the MMT staff, and in particular observer Michael Calkins, for their assistance with these observations.”