EP240919a: Optical upper limit with Kinder observations

We observed the field of the fast X-ray transient EP240919a (Liang et al., GCN 37561, GCN 37564; Jiang et al., GCN 37565; Kumar et al., GCN 37566; Malesani et al., GCN 37567, Lipunov et al., GCN 37570; Rodi et al., GCN 37573; Wang et al., GCN 37574) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024arXiv240609270C). The first SLT epoch of observations started at 16:04 UTC on the 19th of September 2024 (MJD = 60572.669), 1.27 hr after the EP-WXT detection. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked frames, we did not detect any evidence of a new uncataloged source within the EP-FXT error circle of 20" reported by Liang et al. (GCN 37555). Moreover, we utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform the photometry on our stacked frame. The details of the observations and measured 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass SLT | r | 60572.669 | 1.27 hr | 11 * 300 s | >19.8 | 2".19 | 1.46 We did not find any significant source at the specified location by Malesani et al. (GCN 37567). The presented magnitude was calibrated using the field stars from the Pan-STARRS1 catalog, and was not corrected for the expected Galactic foreground extinction of E(B-V) = 0.06 mag (Schlafly & Finkbeiner 2011) in the direction of the transient.