TITLE:   GCN CIRCULAR
NUMBER:  33550
SUBJECT: GRB 230328B : GRANDMA/Kilonova-Catcher optical detection
DATE:    23/03/31 20:37:22 GMT
FROM:    Damien Turpin at NAOC (CAS)  <dturpin-astro@hotmail.com>

F. Kugel (KNC), D. Turpin (CEA), S. Karpov (FZU), T. Hussenot-Desenonges 
(IJCLab), S. Antier (OCA/Artemis), P.A. Duverne (APC, U. Paris Cité),
P. Hello (IJCLab), A. Klotz (OMP/IRAP) report on behalf of the 
GRANDMA/Kilonova-Catcher collaboration:

The Kilonova-Catcher telescope network responded to the alert of 
GRB 230328B (Swift detection: Gropp et al., GCN 33527;
Fermi GBM detection: Veres et al., GCN 33526). 

The KNC observations were taken by F. Kugel with an ARTEMIS CCD ATIK-460ex 
camera mounted in the 0.4-m f/2.8 reflector telescope in the Chante-Perdrix 
Observatory (France).
The afterglow is detected in the 36x60s unfiltered coadded images at
about 5.2 hours (midtime of the exposure) after the Swift/BAT trigger time.

Below, we report our photometric measurement in Rc magnitude.
-------------------------------------------------------------
T-T0 (day)  |Exposure| Filter | Mag +/- err |Mag.Lim. (AB)
-------------------------------------------------------------
0.22172 | 36 x 60s | Rc | 20.19 +/- 0.10 | 21.4 (3 sigma)

Our detection is consistent with the detections and limits previously reported
in Pankov et al., GCN 33528.; Belkin, GCN 33530; Lu et al., GCN 33534;
Catapano et al., GCN 33535; Suresh et al., GCN 33536.; Adami et al., 
GCN 33537; Gompertz et al., GCN 33538; Komesh et al., GCN 33539;
Lu et al., GCN 33540; Ror et al., GCN 33547; Agui Fernandez et al., GCN 33549

The GRANDMA/Kilonova-Cacther images have been calibrated using field
stars from the PanSTARRS-DR1 catalog using the STDpipe pipeline
(Karpov 2022) and the ps1/r to Rc mag conversion from (Pancino et al. 2022).

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/).