GCN Circular 42301
Subject
GRB 251013C: Kilonova-Catcher optical afterglow detection
Event
Date
2025-10-15T20:35:57Z (a day ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
S. Leonini, M. Freeberg, R. Hellot (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration:
We observed the field of GRB 251013C detected by Fermi/GBM (Fermi GBM team, GCN 42221), SVOM/ECLAIRs and GRM (Rakotondrainibe et al., GCN 42223) and AstroSat CZTI (Arya et al., GCN 42246) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC180FL, iT32 and iT72 telescopes operated by M. Freeberg, the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88) operated by S. Leonini and a CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot. Our observations started at TGRB+3.0hr and were taken with Clear, sdss gri and Rc Ic filters.
In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical counterpart firstly reported by SVOM/VT (Palmerio et al., GCN 42223) and later confirmed by many other teams.
We report part of our follow-up results in the table below:
+---------------+----------+------------+----------------+------------------+
| Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument |
+===============+==========+============+================+==================+
| 3.18 | 30 x 30s | Rc (Vega) | 16.29 +/- 0.04 | Montarrenti Obs. |
| 6.47 | 5 x 300s | Rc (Vega) | 17.63 +/- 0.02 | iT72 |
| 8.26 | 6 x 300s | r (AB) | 18.24 +/- 0.05 | CDK17 AITP |
+---------------+----------+------------+----------------+------------------+
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog.
We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023).
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/).