GCN Circular 36139
Subject
EP240416a: Kinder optical counterpart candidate
Date
2024-04-16T19:39:25Z (25 days ago)
From
Janet Chen at National Central University <janetstars@gmail.com>
Via
Web form
T.-W. Chen, A. Aryan (both NCUIA), S. Yang (HNAS), S. J. Smartt (Oxford/QUB), M. Fulton (QUB), W.-J. Hou, H.-Y. Hsiao, C.-H. Lai, Y.-C. Pan, A. Sankar.K, M.-H. Lee, C.-C. Ngeow, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCUIA), J. Gillanders, L. Rhodes, S. Srivastav, H. F. Stevance (all Oxford), T. Moore and K. W. Smith (both QUB) report:
We observed the field of EP240416a (Cheng et al., GCN 36138) using the Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen et al., AstroNote 2021-92). The first LOT epoch of observations started at 16:51 UT on 16 of April 2024 (MJD = 60416.702), 14.15 hours after the EP trigger.
We used the Kinder pipeline (Yang et al. A&A 646, A22) to stack the images and subtract the stacked images with the PanSTARRS1 template images. We detected an optical transient in the difference image, at RA = 13:32:34.514, Dec = -13:37:49.05 (which is 69.6 arcsec away from the reported coordinate of EP240416a by Cheng et al. GCN 36138).
The details of the observations and measured PSF magnitudes (in the AB system) of the possible counterpart of EP240416a are as follows:
Telescope | Filter | MJD | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass
LOT | g | 60416.702 | 14.15 hrs | 300 sec * 7 | 22.39 +/- 0.12 | 1".4 | 1.86
LOT | r | 60416.707 | 14.27 hrs | 300 sec * 7 | 22.08 +/- 0.12 | 1".3 | 1.40
LOT | i | 60416.711 | 14.36 hrs | 300 sec * 7 | 22.02 +/- 0.16 | 1".3 | 1.54
The MJD reported is the start time of the first observation in each band. We observed in a sequence of 300 sec in g,r and i, then 6x300 in r, i, g. All measurements were made on the 7-frame co-adds. The presented magnitudes are calibrated using the field stars from the PanSTARRS1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.05 mag in the direction of the burst (Schlafly & Finkbeiner 2011).
Further follow-up observations are encouraged to identify the nature of this X-ray transient.