TITLE:   GCN CIRCULAR
NUMBER:  43361
SUBJECT: GRB 260109C: Kilonova-Catcher optical upper limit
DATE:    26/01/09 21:03:55 GMT
FROM:    Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>

M. Freeberg (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 260109C detected by Swift/BAT (Parsotan et al., GCN 43359) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iT30 itelescope located at the Siding Spring Observatory and operated by M. Freeberg. Our observations started at TGRB+34.5 min and were taken with Rc filter.

In our stacked frames, subtracted from the SkyMapper DR4 template image, we do not detect any optical counterpart in the Swift/BAT error radius.

We report our follow-up results in the table below:
+---------------+----------+-----------+----------------+-------------+
| Tmid-TGRB (hr)| Exp (s)  | Filter    | Magnitude      | Instrument  |
+===============+==========+===========+================+=============+
| 0.83          | 6 x 300s | Rc (Vega) | 20.8 (5 sigma) | iT30        | 
+---------------+----------+-----------+----------------+-------------+

All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022).  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/).