GCN Circular 39464
Subject
EP250223a: Kinder optical follow-up observations
Event
Date
2025-02-25T01:49:48Z (4 months ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
Web form
A. Aryan (NCU), A. K. H. Kong (NTHU), T.-W. Chen, W.-J. Hou, H.-Y. Hsiao (all 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, C.-S. Lin, J.-K. Guo (all NCU), S. Yang, L. L. Fan, 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 EP250223a (Lian et al., GCN 39429) using the 40cm SLT telescope and Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first SLT epoch of observations in the i-band started at 12:00:02 UT on the 24th of February 2024 (MJD = 60730.500), 20.92 hrs after the EP trigger. The first LOT epoch of observations in the r-band started at 14:42:53 UT on the 24th of February 2024 (MJD = 60730.613), 23.64 hrs after the EP trigger.
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 images, we clearly detected the optical counterpart candidate proposed by Hauptmann et al. (GCN 39436) and confirmed by several other observations (e.g., Levan et al al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin et al., GCN 39453; and O’Neill et al., GCN39455).
We utilized 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 photometry (in the AB system) are as follows:
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Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
SLT | i | 60730.500 | 20.92 | 300 * 24 | 19.23 +/- 0.03 | 2".06 | 1.51
LOT | r | 60730.613 | 23.64 | 300 * 6 | 19.79 +/- 0.01 | 1".43 | 2.10
The presented magnitudes were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_i = 0.16 mag and A_r = 0.22 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011).