TITLE: GCN CIRCULAR NUMBER: 44851 SUBJECT: GRB 260604C: GRANDMA observations DATE: 26/06/06 17:16:35 GMT FROM: antier@ijclab.in2p3.fr L. Chen (TSU), N. Sasaki (UEA,LNA), A. Simon (TShNU of Kyiv), S. Antier (IJCLAB), M. Coughlin (UMN) O. Burkhonov (UBAI), S. Ehgamberdiev (UBAI), Y. Rajabov (UBAI), Y. Tillayev (UBAI), R. Inasaridze (AbAO), N. Kochiashvili (AbAO), V. Zhuzhunadze (AbAO), A. Klotz (IRAP), P. Put (NARIT), K. Noysena (NARIT), A. Manasanun (NARIT), M. Freeberg (KNC), E. Elhosseiny (NRIAG), A. Takey (NRIAG), M. Pillas (IAP), W. Corradi (LNA), T. Leandro de Almeida (LNA), I. Abdusamatjan (TNOT) on behalf of GRANDMA: We conducted follow-up observations of GRB 260604C (Fermi Team, GCN Circ. 44822, Gotz et al., GCN Circ. 44823) with GRANDMA from 0.05 h post T0 (MJD 61195.84859954) up to now. To do this, we have collected data from KNC (Hellot et al., GCN 44835), TAROT/TCH, UBAI-NT60, UBAI-AZT22, AbAO-T70, KAO-1.8m, TRT-SRO, OPD-60, TTT and NOWT. GRB 260604C optical afterglow (reported by Lipunov et al., GCN 44827) is detected at several epochs and a subset of the photometry corrected for Galactic extinction is reported in the public site group of the public ACME service Skyportal/ICARE https://skyportal-icare.ijclab.in2p3.fr/source/GCN-260604_202037. To access, one simply needs to create an account using your ORCID id. Our measurements are in agreement with Lipunov et al., GCN 44827; Konno et al., GCN 44828; Zhu et al., GCN 44832, Becerra et al., GCN 44834; GCN 44835; Gompertz et al., 44843,Saccardi et al. 44844. The observations are performed under the P7 campaign of GRANDMA to monitor SVOM alerts and LSST alerts from explosive fast transients filtered by BOOM/Babamul and FINK. 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 (kilonovacatcher.in2p3.fr). Astrophysics Center for Multimessenger studies in Europe is supported Skyportal/ICARE (contact camille.douzet@ijclab.in2p3.fr, skyportal.io) View this GCN Circular online at https://gcn.nasa.gov/circulars/44851. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...