GCN Circular 36094

A. Aryan (NCUIA), S. Yang (HNAS), T.-W. Chen, W.-J. Hou, C.-H. Lai, A. Sankar.K, Y.-C. Pan (all NCUIA), S. J. Smartt (Oxford/QUB), K. W. Smith (QUB), H.-Y. Hsiao, M.-H. Lee, C.-C. Ngeow, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCUIA), J. Gillanders, L. Rhodes, S. Srivastav (all Oxford), T. Moore and M. Fulton (both QUB) report:

We observed the field of EP240414a (Lian et al., GCN 36091
Not found
 
 
) 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 12:50 UT on 14 of April 2024 (MJD=60414.535), 3.13 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 Legacy Survey DR10 template images. We detected an optical transient candidate in the difference image, at RA=12:46:01.7248, Dec=-9:43:08.872 (which is 1.56 arcmins away from the reported coordinate of EP240414a). We note an extended source in the Legacy Survey image, which is likely its host galaxy. We cross-matched it with the SDSS DR15 catalogue and found it could correspond to the galaxy, SDSS J124601.99-094309.3, with r-band magnitude as 19.04 mag. 

The details of the observations and measured PSF magnitudes (in the AB system) of the possible counterpart of EP240414a are as follows:

Telescope | Filter | MJD | t-t0 | Exposure | Magnitude | Seeing | Airmass
LOT | r | 60414.535 | 3.13 hrs | 300 sec * 6 | 21.52 +/- 0.12 | 1".7 | 1.31 
LOT | i | 60414.564 | 3.68 hrs | 300 sec * 6 | 21.40 +/- 0.16 | 1".2 | 1.43

The presented magnitudes are calibrated using the field stars from the SDSS catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.03 mag in the direction of the burst (Schlafly & Finkbeiner 2011).

Accordint to SDSS, for the likely host galaxy, SDSS J124601.99-094309.3, its photo-z is 0.299 +/- 0.0426, and the distance module is then 40.80. Assuming r-band can be roughly k-corrected to g-band, with the Milky Way extinction correction, the optical counterpart candidate has the rest-frame M_g = -19.07 mag and M_r = -19.18 mag. 

We are still continuously observing this source. Further follow-up observations are encouraged to identify the nature of this X-ray transient. 

We thank the Einstein Probe team for useful communication.