TITLE: GCN CIRCULAR NUMBER: 38254 SUBJECT: EP241115a/GRB 241115D: Optical upper limits with Kinder observations DATE: 24/11/16 15:29:35 GMT FROM: Janet Chen at National Central University janetstars@gmail.com

L. L. Fan (HNAS), A. Aryan, T.-W. Chen, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, H.-C. Lin, C.-H. Lai, W.-J. Hou, C.-S. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:

We observed the field of the fast X-ray transient EP241115a/GRB 241115D (Hu et al., GCN 38239; Dai et al., GCN 38251; Lipunov et al., GCN 38242; SVOM/GRM team + SVOM JSWG, GCN 38250) using the 40cm SLT and 1m LOT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024arXiv240609270C).

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. We do not find any new and uncataloged optical source in the stacked frames within the 4.3-arcsecond error circle of the Swift-XRT localization (Dai et al., GCN 38251).

Moreover, we utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform the PSF photometry on our stacked frames. The details of the observations and measured 3-sigma upper limit (in the AB system) are as follows:

-------------------------------------------------------------------------------------------- The first SLT epoch of observations started at 12:26 UTC on the 16th of November 2024 (MJD = 60630.518), 1.28d after the EP WXT trigger. Telescope | Filter | MJD (start) | t-t0 (d) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | r | 60630.518 | 1.28 | 300 * 6 | > 20.5 | 2".45 | 1.36

-------------------------------------------------------------------------------------------- The first LOT epoch of observations started at 13:06 UTC on the 16th of November 2024 (MJD = 60630.546), 1.30d after the EP WXT trigger. Telescope | Filter | MJD (start) | t-t0 (d) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 60630.546 | 1.30 | 300 * 6 | > 21.7 | 1".44 | 1.33

The presented magnitudes are calibrated using the field stars from the Pan-STARRS1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.02 mag in the direction of the transient (Schlafly & Finkbeiner 2011).

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