TITLE:   GCN CIRCULAR
NUMBER:  38366
SUBJECT: GRB 241127A: GRANDMA and Kilonova-Catcher optical afterglow detections
DATE:    24/11/28 16:24:29 GMT
FROM:    Thomas Hussenot-Desenonges at IJCLab <thomas.hussenot@ijclab.in2p3.fr>

T. Hussenot-Desenonges (IJCLAB), D. Akl (AUS), M. Coughlin (UMN), M. Molham (NRIAG),  S. Agayeva (Shamakhy Obs.),
S. Antier (OCA), C. Andrade (UMN), S. Karpov (FZU), I. Tosta e Melo (UniCT-DFA), P. Hello (IJCLAB), P-A Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS),
M. Masek (FZU), A. Klotz (IRAP), D. Turpin (CEA-Saclay/Irfu), M. Freeberg (KNC), on behalf of the GRANDMA and Kilonova-Catcher collaborations:

We observed the field of GRB 241127A, detected by SWIFT (GCN 38354) and SVOM (GCN 38363) with the GRANDMA network and its citizen science project Kilonova-catcher (KNC). 

Our observations were performed with the TAROT-TCH, FRAM-Auger and the KNC-CHI-1, 60cm telescopes. 

We detect the afterglow already observed by Swift/XRT and UVOT (GCN 38354, 38362, 38364, 38365), MASTER (GCN 38353, 38358) and LCOGT (GCN 38359) and obtain the following magnitudes:

| Tstart (UTC) | Telescope | Exposure | Filter | Magnitude |

| 2024-11-28T00:33:05 | FRAM-Auger | 20x120s | R | 18.78 +- 0.20 (Vega)|
| 2024-11-28T00:50:45 | TAROT-TCH  | 4x180s | R  | 19.14 +- 0.17 (Vega)|
| 2024-11-28T01:16:26 | KNC-CHI-1  | 2x120s | r' | 19.4 +- 0.1 (AB) |
| 2024-11-28T01:20:52 | KNC-CHI-1  | 2x120s | g' | 19.74 +- 0.09 (AB) |

All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). TCH and KNC images were calibrated using the SkyMapper DR4 catalogue, the FRAM-Auger image used Gaia DR3 Synphot. 
The data are not corrected from Galaxy extinction.

Our magnitudes are consistent with those reported by LCOGT in GCN 38359.

We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023)
A report of the observations of GRANDMA for this source can be seen at:
https://skyportal-icare.ijclab.in2p3.fr/public/sources/GRB241127


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/).