TITLE:   GCN CIRCULAR
NUMBER:  40777
SUBJECT: GRB 250617B: Kilonova-Catcher optical afterglow detection
DATE:    25/06/18 11:19:22 GMT
FROM:    Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>

D. Turpin (CEA-Saclay/Irfu), M. Freeberg (KNC), C. Andrade(UMN), M. Pillas (ULiege), M. Tanasan (NARIT), S. Antier (OCA/IJCLAB) on behalf of the GRANDMA/Kilonova-Catcher collaboration:

We observed the field of GRB 250617B (Page et al., GCN 40760) detected by Swift/BAT with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL telescope operated by M. Freeberg starting from T_GRB+10hr. 

In our stacked frames, subtracted from the PanSTARRS DR2 template image, we marginally detect the optical afterglow at the position reported by Swift/UVOT (Page et al., GCN 40760), SAO RAS (Moskvitin et al., GCN 40761), Ondrejov D50 (Jelinek et al., GCN 40762), NUTTelA-TAO (Grossan et al., GCN 40771), SVOM/VT (Mat et al., GCN 40772), NOT (Schneider et al., GCN 40774), COLIBRÍ (Antier et al., GCN 40775) and VLT/X-shooter (Corcoran et al., GCN 40776)

We report our follow-up results in the table below:
+---------------+-------------+--------------+----------------+--------------+
| Tmid-TGRB (hr)| Exp (s)     | Filter       | Magnitude      | Instrument   |
+===============+=============+==============+================+==============+
| 10.8          | 18 x 300s   | r (AB)       | 20.85 +/- 0.29 | TEC160FL     | 
+---------------+-------------+--------------+----------------+--------------+

All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan images were calibrated using the PanSTARRS DR1 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/).