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GCN Circular 36395

Subject
GRB 240502C: Zeiss-1000 at Koshka observatory observations of GOTO optical counterpart candidates
Date
2024-05-05T09:17:11Z (13 days ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
Via
legacy email
S. Belkin (IKI),  A. Novichonok (Petrozavodsk State University, KIAM), A. Pozanenko (IKI), N. Pankov (HSE,IKI) report on behalf of GRB IKI FuN:

We observed possible optical counterpart candidates of the GRB 240502C (Fermi GBM Team, GCN 36376) reported by Gompertz et al. (GCN 36380) with the Zeiss-1000 telescope at Koshka observatory (INASAN) in R-filter on 2024-05-13. Preliminary photometry of stacked images is the following

Name   Date    UT start  t-T0   Exp.  Filter     OT     Err.  UL(3sigma)
                             (mid, days)      (s)

GOTO24bao 2024-05-03 20:58:29 1.65611 15x120 R 19.24(OT+Host) 0.08 21.3
GOTO24azq 2024-05-03 21:34:06 1.68084 15x120 R 20.20          0.17 21.4
GOTO24bar 2024-05-03 22:06:55 1.70363 15x120 R 19.05(OT+Host) 0.07 21.0

The photometry is based on nearby USNO-B1.0 stars.
Ref.stars
USNO-B1.0
RA DEC R2
10:45:21.4440000 +63:19:42.470400 15.27
10:45:02.1088800 +63:24:07.632000 17.00
10:45:19.0320000 +63:24:02.682000 15.74

Photometry of the GOTObar (OT+Host) is dimmer than the underlying host galaxy (R~18.7 using Lupton transformation), which might indicate that the source either faded away or wasn't related to the GRB 240502C.

The magnitude of the GOTO24bao (OT+Host) is brighter than the underlying host galaxy (R~20.0 using Lupton transformation), and after host subtraction is R~20.0. This value seems to be fainter than the one reported by Gompertz et al. (GCN 36380). Nevertheless, we cannot ascertain the nature of this candidate using currently available data.

GOTO24azq is clearly visible in the stacked image; however, it doesn't show GRB-like behaviour on a two-day time scale in comparison with the reported magnitude by Gompertz et al. (GCN 36380).

Further observations might be needed to confirm the connection of these candidates with the GRB 240502C.


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