TITLE: GCN CIRCULAR NUMBER: 37108 SUBJECT: EP240807a: STEP/T80S optical limits DATE: 24/08/08 22:35:04 GMT FROM: André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos@gmail.com> A. Santos (CBPF), L. Santana-Silva (CBPF), C. R. Bom (CBPF), C. D. Kilpatrick (Northwestern), P. Darc (CBPF), C. Mendes de Oliveira (IAG-USP) report on behalf of the STEP collaboration: We conducted optical follow up with the T80S 0.8-m robotic telescope (Santos et al., 2024, MNRAS, 529, 59) of the fast X-ray transient EP240807a discovered by the Einstein Probe (GCN [36691](https://gcn.nasa.gov/circulars/36691). EP240807a was temporally coincident with the Fermi-GBM alert from GRB240807A (GCN 37089) and subsequently localized by the Follow-up X-ray Telescope (FXT) on Einstein probe (GCN 37097). The T80S observations started on August 8 07:40 UT (~16 hours after the trigger). We obtained images totaling 360s (2x180s) in g-band and 720s (3x240s) in r-band with the T80S camera centered at the position of the FXT counterpart at R.A.=20:03:52.90 and Decl.=-68:46:37.20 (J2000). Subtracting DECAM template images from the T80S frames using photpipe (Rest et al., 2005), we do not detect any transient source in our difference images and derive 3-sigma limiting magnitudes of g > 21.9 and r > 22.2 mag for any optical transient. View this GCN Circular online at https://gcn.nasa.gov/circulars/37108. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...