TITLE:   GCN CIRCULAR
NUMBER:  37773
SUBJECT: GRB 241009A: GRANDMA optical upper limits
DATE:    24/10/11 19:41:48 GMT
FROM:    Thomas Hussenot-Desenonges at IJCLab <thomas.hussenot@ijclab.in2p3.fr>

T. Hussenot-Desenonges (IJCLAB), Y. Rajabov (UBAI), A. Tanasan (NARIT), I. Abdi (AUS), R.Strasbaugh (EIU), M.Lamoureux (UCLouvain), S. Antier (OCA), S. Karpov (FZU), M. Coughlin (UMN), C. Andrade (UMN), I. Tosta e Melo (UniCT-DFA), P. Hello, N. Leroy (IJCLAB), P-A Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS), A. Klotz (IRAP/OMP), C. Limonta, M .Boer (OCA), M. Masek, M. Prouza (FZU), D.Turpin (CEA-Saclay/Irfu), M. Freeberg, D. St-Gelais (KNC)
on behalf of the GRANDMA collaboration.

We observed the field of GRB 241009A, detected by SVOM/ECLAIRs (GCN 37749) with the GRANDMA network and its citizen science project Kilonova-catcher (KNC). Our observations started with TAROT-Reunion (TRE), 36 min after the trigger.

We did not detect any uncatalogued optical sources in the error region of SVOM/ECLAIRs, with the following 5-sigma upperlimits on the field:

| Tstart (UTC)  | Telescope | Exposure | Filter | U.L. |
	 	 	 	
| 2024-10-09T19:53:31 | TAROT-TRE | 32x60s | Clear (G) | 18.7 (Vega) |
| 2024-10-09T21:13:08 | FRAM-CTA-N | 17x120s | R | 18.4 (Vega) |
| 2024-10-09T22:25:02 | KNC-HakosRC360 | 19x180s | sdssr | 19.8 (AB) |
| 2024-10-09T23:39:34 | FRAM-Auger | 15x120s | R | 18.2 (Vega) |
| 2024-10-10T02:16:21 | KNC-Obs. Laurier | 41x60s | R | 19.1 (Vega) |

In particular, within these upperlimits, we do not detect any optical counterpart of the Swift-XRT afterglow position candidate (RA 21h 40m 02.08s DEC -35° 39′ 34.0″) (GCN 37772).

Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 Synphot catalog. Images obtained with Sloan filters were calibrated using the SkyMapper DR4 catalog. The unfiltered image taken by TAROT-TRE was calibrated as a Gaia G image using the Gaia eDR3 catalogue.

All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). We use the SkyPortal application (skyportal.io) to monitor our observational campaign.

We thank the SVOM collaboration for useful communication.

GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).