1. Discovery of the optical and radio counterpart to the fast X-ray transient EP240315a
- Author
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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., and Young, D. R.
- Subjects
Astrophysics - High Energy Astrophysical Phenomena - 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)
- Published
- 2024