TITLE:   GCN CIRCULAR
NUMBER:  36707
SUBJECT: EP240617a: STEP/T80S optical limits
DATE:    24/06/19 23:42:54 GMT
FROM:    André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos@gmail.com>

A. Santos (CBPF), C. R. Bom (CBPF), C. D. Kilpatrick (Northwestern), L. Santana-Silva (CBPF), P. Darc (CBPF), C. Mendes de Oliveira (IAG-USP) report on behalf of the STEP collaboration:


We conducted optical follow up of the fast X-ray transient EP240617a by the Einstein Probe (GCN [36691](https://gcn.nasa.gov/circulars/36691), [36692](https://gcn.nasa.gov/circulars/36691)) with the T80S 0.8-m robotic telescope using the 1.4 x 1.4 field-of-view T80S-Cam imager (see Santos et al., 2024, MNRAS, 529, 59 for details). The observations started on June 19, 05:10 UT (~41 hours after the trigger). We obtained 360s (3x120s) images in both i and z bands with the T80S camera centered at R.A.=19:00:07.29 and Decl.=-22:33:39.60 (J2000).  Subtracting Pan-STARRS 3pi template images from the T80S frames using photpipe (Rest et al., 2005), we do not detect any sources in our difference images and derive 3-sigma limiting magnitudes of z > 20.6 and i > 20.9 mag for any optical transient.