TITLE: GCN CIRCULAR NUMBER: 39218 SUBJECT: EP trigger 01709131361 (possible EP250207a): NOT optical observations and flaring star DATE: 25/02/07 23:22:16 GMT FROM: Andrew Levan at Radboud University a.levan@astro.ru.nl
A. J. Levan (Radboud Univ and Warwick Univ.), A. van Hoof (Radboud Univ.), A. Martin-Carrillo (UCD), D.B. Malesani (DAWN/NBI and Radboud Univ.), F.E. Bauer (PUC), P.G. Jonker (Radboud Univ), G. Leloudas (DTU Space) and B. Milvang-Jensen (DAWN/NBI) report for a larger collaboration:
We obtained observations of the field of the EP WXT transient (EP250207.660, trigger ID: 01709131361) with the Nordic Optical Telescope. Observations in the r-band began on 2025 Feb 7.8487 UT (4.5 hr after the EP trigger).
Comparison to legacy survey observations does not reveal any plausible extragalactic counterparts to the source, consistent with earlier optical observations (Busman et al. GCN 39214), although we do note a bright galaxy at (RA=23:47:37.96, DEC=27:00:59.7) with a Legacy Survey photometric redshift of z = 0.07 +/- 0.01 (Zhou et al. 2021, MNRAS, 501, 3309) within the error box.
We also note a bright flare from a high-proper motion M9 dwarf within the error box. The source is currently located at
RA(J2000) = 23:47:37.44 DEC(J2000) = 27:02:06.9
It has brightened from an archival magnitude of r = 19.8+/-0.1 (Pan-STARRS) to r = 16.9+/-0.1. However, the source is identified in the Gaia DR3 catalog with a proper motion of 315.33 +/- 0.21 mas/yr. This implies it is a high proper motion, nearby star (parallax 46.76 +/- 0.16 mas) undergoing a high amplitude (+3 mag) flare. It is likely, though not conclusive, that this flare was related to the EP trigger. However, the absence of the flare in observations taken 2.5 hours earlier (Busman et al. GCN 39214) could also mean they are unrelated.
We thank the observers, Fabian Mattig and Max Pritzkuleit for their excellent support in obtaining these observations.
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