TITLE:   GCN CIRCULAR
NUMBER:  36497
SUBJECT: GRB 240502C: Zeiss-1000 at Koshka observations of GOTO24bao optical counterpart candidate
DATE:    24/05/16 16:13:56 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>

A. Volnova (IKI), A. Novichonok (Petrozavodsk State University, KIAM), A. Pozanenko (IKI), S. Belkin (IKI),  N. Pankov (HSE) report on behalf of GRB IKI FuN:

We observed GOTO24bao (Gompertz et al., GCN 36380; Belkin et al., GCN 36395), a possible optical counterpart of the GRB 240502C (Fermi GBM Team, GCN 36376) with the Zeiss-1000 telescope of Koshka observatory in R-filter on 2024-05-05/06. The preliminary photometry of stacked images in all epochs is as follows

Date       UT start  t-T0     Exp. Filter OT Err. UL (3sigma)
             (mid, days)  (s)
2024-05-03 20:58:29 0.99542  15x120   R 19.02 0.06 21.1  
2024-05-05 18:58:54 2.89875   8x300   R 18.73 0.04 21.3 
2024-05-06 20:48:24 3.97479   8x300   R 18.98 0.04 21.8  

Ref. stars
USNO-B1.0
RA DEC R2
09:57:18.15288  +62:02:45.8412  17.46
09:56:49.99872 +62:01:39.1620  14.74
09:57:14.13480  +61:59:47.1624  16.44

The magnitude of the (possible OT + host) on May 5 is somewhat but significant) brighter than in adjacent epochs, indicating the presence of variability of the OT. Till now we cannot  confirm the association of the  candidate GOTO24bao with an GRB 240502C afterglow.