TITLE: GCN CIRCULAR NUMBER: 38344 SUBJECT: EP241126a: Optical Upper limits with Kinder observations DATE: 24/11/27 13:42:19 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) amararyan941@gmail.com
C.-H. Lai, A. Aryan, T.-W. Chen, Y. J. Yang, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, H.-C. Lin, W.-J. Hou, H.-Y. Hsiao, 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 field of the fast X-ray transient EP241126a (Hu et al., GCN 38335, Fu et al., GCN 38337; Li et al., GCN 38338; Zheng et al., GCN 38339) using the 1m LOT at the Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024 arXiv:2406.09270). The first LOT epoch of observations started at 11:53 UTC on 27th November 2024 (MJD 60641.495), 16.23 hr after the EP-WXT trigger.
We utilize 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 our combined frame, we do not detect the optical counterpart proposed by Fu et al. (GCN 38337). The optical counterpart seems to have faded beyond our detection limit.
Moreover, we utilize the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on our stacked frames. The details of the observations and measured 3-sigma limits (in the AB system) are as follows:
------------------------------------------------------------------------------------------------------ Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 60641.495 | 16.23 | 300 * 6 | > 22.5 | 1".37 | 1.10
The presented magnitude was calibrated using the field stars from the Pan-STARRS1 catalog and was not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_r = 0.38 mag in the direction of the transient (Schlafly & Finkbeiner 2011).
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