TITLE: GCN CIRCULAR NUMBER: 39278 SUBJECT: Gemini-South spectroscopic redshift of EP250207b host galaxy candidate (z=0.082) DATE: 25/02/11 08:35:07 GMT FROM: Andrew Levan at Radboud University a.levan@astro.ru.nl
Andrew J. Levan (Radboud), Daniele B. Malesani (DAWN/NBI and Radboud), Peter G. Jonker (Radboud), Jonathan A. Quirola-Vásquez (Radboud), Javi Sánchez-Sierras (Radboud), Antonio Martin-Carrillo (UCD), Franz E. Bauer (PUC), report on behalf of a larger collaboration:
We obtained spectroscopic observations of the candidate host galaxy WISEA J111002.65-075211.9 of EP 250207b (Zhou et al., GCN 39266) with the Gemini South telescope and the GMOS spectrograph. A total of 4x180 s observations were obtained, covering the spectral range 3600-7600 AA, with a mean time of about 3.3 days after the high-energy transient.
The spectrum is clearly that of a quiescent galaxy with no detectable emission lines. From a provisional reduction, we identify the presence of Ca H&K, Mg I, and Na I D absorption and determine a redshift of z = 0.082.
The galaxy is unlike those of collapsar GRBs, consistent with the non-detection of any counterpart in deep imaging (Malesani et al. GCN 39270), which also rules out any FBOT-like emission similar to that seen in other recent FXTs. If this is the host of EP 250207b a possibility is that the transient was created via a compact object merger. However, given the large (10” radius) X-ray error localisation we caution that an origin in a higher redshift system in chance projection to the z=0.082 galaxy remains plausible. We encourage further observations to search for the optical/IR counterpart.
We thank the staff of Gemini, in particular Jeong-Eun Heo, for their excellent support in securing these observations.
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