TITLE: GCN CIRCULAR NUMBER: 38293 SUBJECT: EP trigger ID 01709065118: Keck/LRIS spectroscopic observations DATE: 24/11/22 03:37:43 GMT FROM: Weikang Zheng at UC Berkeley <weikang@berkeley.edu> WeiKang Zheng, Thomas G. Brink, Alexei V. Filippenko (UC Berkeley), and Yi Yang (Tsinghua Univ., Beijing), report on behalf of the KAIT GRB team: We observed the M-type star 1RXS J225817.2-110434, the optical counterpart of an EP flare event (trigger ID 01709065118; Zhou et al., GCN 37715; Zheng et al., GCN 37733), with the Low Resolution Imaging Spectrometer (LRIS; Oke et al. 1995) on the Keck I 10 m telescope. Observations were performed on Oct. 5, 2024 UTC, with the 600/4000 grism and 400/8500 grating. Two spectra with exposure times of 60 s and 80 s were obtained at 07:26 and 09:46 UTC, corresponding to 1.72 and 4.05 hr (respectively) after the EP/WXT trigger time. The spectra exhibit a red continuum flux with strong superposed hydrogen Balmer emission lines as well as Ca II H&K and TiO emission lines, consistent with a typical dMe star spectrum. Moreover, the flux of the Balmer emission lines dropped by nearly half between the two epochs. The continuum below 3500 Ang also dropped significantly. This is consistent with the light-curve behavior reported by Lick/KAIT (Zheng et al., GCN 37733), where the star brightness decreased after the EP/WXT trigger. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. View this GCN Circular online at https://gcn.nasa.gov/circulars/38293. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...