TITLE:   GCN CIRCULAR
NUMBER:  38042
SUBJECT: Kinder optical follow-up observations of EP241021a, EP241026b, and EP241030a/GRB241030A 
DATE:    24/11/02 13:01:46 GMT
FROM:    Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>

A. Aryan (NCU), A. K. H. Kong (NTHU), W.-J. Hou, T.-W. Chen (both NCU), 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, H.-Y. Hsiao, C.-S. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, 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 fields of the fast X-ray transients EP241021a (rebrightening; Quirola-Vasquez et al. GCN 37930, Freeburn et al. GCN 37942, Bochenek et al. 38030), EP241026b (Lian et al. GCN 37902, Lipunov et al. GCN 37905, Mohan et al. GCN 37920, Rossi et al. GCN 37938, Lian et al. GCN 37967, Bochenek et al. GCN 38018), and EP241030a/GRB241030A (Wu et al. GCN 37997, Fermi GBM Team, GCN 37955, Lipunov et al. GCN 38007, Busmann et al. GCN 38019, Liang et al. GCN 38026, Li et al. GCN 38027, Moskvitin et al. GCN 38032, Yan et al. GCN 38035, Liang et al. GCN 38040) using the 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. 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 photometry and 3-sigma limit (in the AB system) for each of the sources are as follows:

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EP241021a: The first epoch of observations started at 2024-11-01, 15:44:21 UT.
Telescope | Filter | MJD (start) | t-t0 (d) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
LOT | r | 60615.656 | 11.44 | 300 * 6 | 22.06 +/- 0.33 | 1".02 | 1.08

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EP241026b: The first epoch of observations started at 2024-11-01, 16:19:08 UT.
Telescope | Filter | MJD (start) | t-t0 (d) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
LOT | r | 60615.680 | 5.92 | 300 * 12 | > 23.4 | 1".08 | 1.05

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EP241030a: The first epoch of observations started at 2024-11-01, 13:42:34 UT in r-band.
Telescope | Filter | MJD (start) | t-t0 (d) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
LOT | r | 60615.571 | 2.30 | 300 * 6 | 21.73 +/- 0.36 | 1".39 | 1.90
LOT | g | 60615.593 | 2.32 | 300 * 6 | 22.00 +/- 0.42 | 1".50 | 1.95

The presented magnitudes are calibrated using field stars from the Pan-STARRS1 catalog and are not corrected for the expected Galactic foreground extinction.