TITLE: GCN CIRCULAR NUMBER: 38449 SUBJECT: EP241113a: Keck/LRIS spectroscopic observation and tentative redshift DATE: 24/12/06 14:19:47 GMT FROM: Jonathan Quirola at Radboud University jaquirola1990@gmail.com
J. A. Quirola-Vasquez (Radboud Univ.), P. G. Jonker (Radboud Univ.), D. Stern (JPL/Caltech), F. Harrison (Caltech), A. Rodriguez (Caltech), J. van Dalen (Radboud Univ.), D. B. Malesani (DAWN/NBI & Radboud Univ.), A. J. Levan (Radboud Univ. & Warwick Univ.), J. C. Rastinejad (Northwestern Univ.), A. van Hoof (Radboud Univ.), J. Sanchez-Sierras (Radboud Univ.), F. E. Bauer (PUC), A. Rossi (INAF/OAS), M. E. Ravasio (Radboud Univ.) report on behalf of a larger collaboration:
We observed the optical counterpart (Rossi et al., GCN 38233) of the X-ray transient EP241113a (Liu et al., GCN 38211) with the Low-Resolution Imaging Spectrometer (LRIS; Oke et al. 1995) on the Keck I 10 m telescope. Observations were performed on 2024 Nov. 30 starting at 13:24:00 UT (i.e., ~16.76 days after the trigger), with the 600/4000 grism and 400/8500 grating for the blue and red arms, respectively. A total of 3 observations of 1000 s each were secured. The covered wavelength range is 3200 to 11000 AA.
The LRIS spectrum at the position of EP241113a shows a low signal-to-noise trace, likely corresponding to the host galaxy of the transient. A single, weak emission line is detected at 9420 Å. Among the possible interpretations, we favor [O II] at z = 1.53, due to the lack of any other lines which would be expected if the line were [O III] (at z = 0.88) or H-alpha (at z = 0.44). The resolution of the slit-grating combination (6.9 Å FWHM) is such that we do not expect to resolve the two components of the [O II] doublet for a low S/N line.
We caution that, due to the lack of detection of other emission or absorption lines, the redshift z = 1.53 should be considered tentative.
Finally, our slit covers the galaxy 2MASX J08480182+5222544, 20" away from the transient (in projection), and for that object, we confirm the redshift of z = 0.115 using, among other lines, the detection of [O II], H-alpha, [N II], [S II]. No lines are detected at this redshift at the transient position, which makes an association between these two objects unlikely.
The data presented herein were obtained at the W. M. Keck Observatory, which operates as a scientific partnership between the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. We thank the staff of the Keck Observatory for their excellent support.
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