TITLE:   GCN CIRCULAR
NUMBER:  34346
SUBJECT: GRB 230805B: NOT optical afterglow confirmation
DATE:    23/08/05 22:58:50 GMT
FROM:    Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>

D. B. Malesani (Radboud Univ. and DAWN/NBI) and T. Pursimo (NOT) report on behalf of a larger collaboration:

We observed the location of GRB 230805B (Cenko et al., GCN 34339) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were secured in the r and z bands. An object with position consistent with the one reported by Moskvitin & Goranskij (GCN 34343) is well detected in our data. Based on nearby stars from the Gaia catalog, we measure the following J2000 coordinates, with an error of ~0.3":

RA  = 13:50:58.23
Dec = +31:11:28.6

At a mean epoch 2023 Aug 5.91 UT (10.4 hr after the trigger), we measure a preliminary magnitude (calibrated against nearby Pan-STARRS point-like sources) r = 23.5 +- 0.15 AB. Compared to the measurement by Moskvitin & Goranskij (GCN 34343), our magnitude value provides 2-sigma evidence for fading, consistent with afterglow behavior.