TITLE: GCN CIRCULAR NUMBER: 45030 SUBJECT: EP260623a: Optical follow-up observations with Kinder DATE: 26/06/23 16:42:04 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com> M.-H. Lee, A. Aryan, T.-W. Chen, W.-J. Hou (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), S. Yang(HNAS), A. Sankar.K, K. N.-T. Ho, A. Dutta, Y.-H. Lee, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, H.-Y. Hsiao, C.-S. Lin, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), K. W. Smith, H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260623a (Wang et al., GCN 45020) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in r-band started at 15:26 UTC on the 23rd of June 2026 (MJD 61214.6431), 12.53 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. Next, we employed the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. In the difference image, the optical counterpart (Li et al., GCN 45021; Izzo et al., GCN 45022; Angulo et al., GCN 45024; Brivio et al., GCN 45025; Jiang et al., GCN 45026; Li et al., GCN 45027; and Jelinek et al., GCN 45029) was clearly detected. Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and measured photometry (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 61214.6431 | 12.53 | 300 * 6 | 20.74 +/- 0.07 | 1".97 | 1.91 The presented magnitudes are calibrated using the field stars from ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). The reported magnitude is not corrected for an expected galactic extinction of A_r = 0.32 mag, in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/45030. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...