GCN Circular 37575
Subject
EP240919a: Optical upper limit with Kinder observations
Date
2024-09-20T14:32:59Z (3 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), Y. J. Yang, T.-W. Chen, C.-H. Lai, H.-Y. Hsiao, C.-S. Lin (all NCU), S. Yang (HNAS), S. J. Smartt (Oxford/QUB), A. Sankar. K, W.-J. Hou, C.-C. Ngeow, M.-H. Lee, Y.-C. Pan, H.-C. Lin, J.-K. Guo (all NCUIA), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, J. Gillanders, 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 EP240919a (Liang et al., GCN 37561, GCN 37564; Jiang et al., GCN 37565; Kumar et al., GCN 37566; Malesani et al., GCN 37567, Lipunov et al., GCN 37570; Rodi et al., GCN 37573; Wang et al., GCN 37574) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024arXiv240609270C). The first SLT epoch of observations started at 16:04 UTC on the 19th of September 2024 (MJD = 60572.669), 1.27 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. In the stacked frames, we did not detect any evidence of a new uncataloged source within the EP-FXT error circle of 20" reported by Liang et al. (GCN 37555).
Moreover, we utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform the photometry on our stacked frame. The details of the observations and measured 3-sigma upper limit (in the AB system) are as follows:
Telescope | Filter | MJD (start) | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass
SLT | r | 60572.669 | 1.27 hr | 11 * 300 s | >19.8 | 2".19 | 1.46
We did not find any significant source at the specified location by Malesani et al. (GCN 37567).
The presented magnitude was calibrated using the field stars from the Pan-STARRS1 catalog, and was not corrected for the expected Galactic foreground extinction of E(B-V) = 0.06 mag (Schlafly & Finkbeiner 2011) in the direction of the transient.