TITLE: GCN CIRCULAR NUMBER: 36010 SUBJECT: X-ray transient EP240331A: GRANDMA-Kilonova catcher optical upper limit DATE: 24/04/02 13:41:41 GMT FROM: Sarah Antier at OCA <sarah.antier@oca.eu> M. Freeberg (KNC), S. Antier (OCA), X. Wang (Tsinghua), W. M Yuan (NAOC), D. Turpin (CEA-Saclay/Irfu), M. Masek (FZU), M. Prouza (FZU), S. Karpov (FZU), I. Tosta e Melo (UniCT-DFA), P. Hello (IJCLAB), T. Pradier (Unistra/IPHC), M. Coughlin (UMN), C. Andrade (UMN), P-A Duverne (APC), N. Guessoum (AUS), H-B Eggenstein (KNC): on behalf of the GRANDMA collaboration: We performed a target of opportunity observations with GRANDMA and its citizen science project Kilonova-catcher (KNC) on the X-ray flare EP20240331a detected by Einstein Probe (EP) WXT on T0 = 2024-03-31T22:07:17 (Pan et al.,2024, ATel #16564). We did not find any optical counterpart : a) using FRAM-CTA-N within 25 arcmin error box centered at 11:17:39.36 -20:02:31.20 (RA,DEC= 169.414, -20.042) on 2024-04-01 23:59:15.000 (1.07 day post T0). Our image limiting magnitudes are Rc = 19 and V = 19 (Vega) b) using KNC-T72 (Chile) within a 20 arcmin error box centered at 11:17:39.36 -20:02:31.20 (RA,DEC= 169.414, -20.042) on 2024-04-02 02:01:20.00 (1.16 day post T0). Our image limiting magnitude is Rc = 20.5 (Vega) Images were calibrated with Gaïa Catalog, using STDpipe (Karpov, 2020). These results are consistent with Groot et al., GCN 36007 and Lipunov et al., GCN 36009. We thank the Einstein Probe team for useful communication. 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/). View this GCN Circular online at https://gcn.nasa.gov/circulars/36010. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...