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GCN Circular 36105

EP 240414a: NOT optical counterpart confirmation
2024-04-15T04:54:28Z (a month ago)
Dong Xu at NAOC/CAS <>
D. Xu (NAOC), D.B. Malesani (DAWN/NBI & Radboud), P. Jonker (Radboud), Z.P. Zhu, X. Liu, S.Y. Fu, S.Q. Jiang, J. An, T.H. Lu (NAOC), M. Turkki (U. of Helsinki, NOT) report on behalf of a large collaboration:

We observed the field of the X-ray transient detected by Einstein Probe, EP 240414a, using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 22:07:38UT on 2024-04-14, i.e., 12.29 hr after the EP trigger and 5 x 300 s r-band frames were obtained.

The previously reported optical counterpart candidate by LOT (Aryan et al., GCN 36094) is clearly detected in our stacked image with coordinates

R.A. = 12:46:01.67 (J2000)
Dec. = -09:43:08.8 (J2000)

which has r = 21.9 +/- 0.1 (AB) at a median time of 0.521 day post-trigger. Comparison of the two observations shows that the source was decaying slowly.

We also searched for other potential counterparts in the NOT image which covers most of the EP/WXT error region, and didn't find any other credible candidate via image subtraction.

We thus confirm that the LOT candidate is the optical counterpart of EP 240414a.

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