TITLE:   GCN CIRCULAR
NUMBER:  37892
SUBJECT: EP241021a:  optical follow-up observations with Xinglong Observatory
DATE:    24/10/26 14:05:37 GMT
FROM:    Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>

J.J-Jin(NAOC),H.Y. Mu(NAOC), Z.F(NAOC),Y.G. Sun, S.L, R.Wang Y.M Mao report on behalf of a large collaboration:
Following the detection of EP241021a by EP-WXT (Hu et al., GCN 37834), we observed the field of EP241021a using the 80-cm telescope at Xinglong Observatory, NAOC. We obtained 3x600s g-band frames with a median time of 2024-10-22T15:25:50 i.e., 34 hr after the EP trigger.No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle.
Then we performed photometry on the Xinglong 2.16-m telescope with a median time of 2024-10-23T15:57:29 i.e., 58 hr after the EP trigger, and obtained 3x600s V-band frames. 
Within the error circle of the EP/WXT, we we detected the optical counterpart of EP241021a, at a position matching the optical counterpart identified by Fu et al., GCN 37840 (see also Gompertz et al., GCN 37835; Lipunov et al., GCN 37839; Fu et al., GCN 37842; Yang et al., GCN 37843; Li et al., GCN 37844; Li et al., GCN 37846; Zheng et al., GCN 37849; Moskvitin et al., GCN 37850; Pugliese et al., GCN 37852; Pérez-Fournon et al., GCN 37858; Bochenek et al., GCN 37869; Kumar et al., GCN 37875). 

We performed aperture photometry on the stacked g and V-band images and calibrated them with Pan-STARRS sources in the field. The observed magnitudes are as follows: 

Date_obs     |  Telescope|   UT    |  Exp. Time     |    Filter   |  Mag    |  Mag_err

----------------------------------------------------------------------------------------
2024-10-22  |  80-cm  |  15:25:50  |  3x600s       |   g      |  *21.51  |  0.032

2024-10-23  |  216-cm |  15:57:29  |  3x600s       |   V      |  22.468  |  0.477