EP250815a: EP-FXT localization and potential association with the outburst of MAXI J1816-195
ATel #17339; W.-J. Zhang (NAO, CAS), C.-Y. Dai (NJU), H. Sun (NAO, CAS) report on behalf of the Einstein Probe (EP) team:
on 16 Aug 2025; 15:08 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)
Subjects: X-ray, Transient
Following the detection of the X-ray transient EP250815a (ATel #17338), we performed a follow-up observation with the Follow-up X-ray Telescope (FXT) onboard the Einstein Probe. The observation started at 2025-08-16T11:45:20 (UTC). Result of the onboard processing of the quick-look data, received as quick alert message, shows that a bright X-ray source was detected at a position of R.A. = 274.2159 deg, DEC = -19.6319 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). This position is 8.7 arcsec away from the accreting millisecond X-ray pulsar MAXI J1816-195 (ATEL #15418, #15421, #15425, #15467), indicating that EP250815a is possibly a new outburst of this X-ray binary. Further observations are required to confirm the association.
Launched on January 9, 2024, EP is a space X-ray observatory designed to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE, and CNES.
