학술논문
Discovery of the optical and radio counterpart to the fast X-ray transient EP240315a
Document Type
Working Paper
Author
Gillanders, J. H.; Rhodes, L.; Srivastav, S.; Carotenuto, F.; Bright, J.; Huber, M. E.; Stevance, H. F.; Smartt, S. J.; Chambers, K. C.; Chen, T. -W.; Fender, R.; Andersson, A.; Cooper, A. J.; Jonker, P. G.; Cowie, F. J.; deBoer, T.; Erasmus, N.; Fulton, M. D.; Gao, H.; Herman, J.; Lin, C. -C.; Lowe, T.; Magnier, E. A.; Miao, H. -Y.; Minguez, P.; Moore, T.; Ngeow, C. -C.; Nicholl, M.; Pan, Y. -C.; Pignata, G.; Rest, A.; Sheng, X.; Smith, I. A.; Smith, K. W.; Tonry, J. L.; Wainscoat, R. J.; Weston, J.; Yang, S.; Young, D. R.
Source
Subject
Language
Abstract
Fast X-ray Transients (FXTs) are extragalactic bursts of soft X-rays first identified >10 years ago. Since then, nearly 40 events have been discovered, although almost all of these have been recovered from archival Chandra and XMM-Newton data. To date, optical sky surveys and follow-up searches have not revealed any multi-wavelength counterparts. The Einstein Probe, launched in January 2024, has started surveying the sky in the soft X-ray regime (0.5-4 keV) and will rapidly increase the sample of FXTs discovered in real time. Here, we report the first discovery of both an optical and radio counterpart to a distant FXT, the fourth source publicly released by the Einstein Probe. We discovered a fast-fading optical transient within the 3 arcmin localisation radius of EP240315a with the all-sky optical survey ATLAS, and our follow-up Gemini spectrum provides a redshift, z=4.859+/-0.002. Furthermore, we uncovered a radio counterpart in the S-band (3.0 GHz) with the MeerKAT radio interferometer. The optical (rest-frame UV) and radio luminosities indicate the FXT most likely originates from either a long gamma-ray burst or a relativistic tidal disruption event. This may be a fortuitous early mission detection by the Einstein Probe or may signpost a mode of discovery for high-redshift, high-energy transients through soft X-ray surveys, combined with locating multi-wavelength counterparts.
Comment: Updated to match version accepted for publication in ApJL (17 pages, 4 figures, 2 tables)
Comment: Updated to match version accepted for publication in ApJL (17 pages, 4 figures, 2 tables)