In recent years, millisecond-duration radio signals originating in distant galaxies appear to have been discovered in the so-called fast radio bursts1,2,3,4,5,6,7,8,9. These signals are dispersed according to a precise physical law and this dispersion is a key observable quantity, which, in tandem with a redshift measurement, can be used for fundamental physical investigations10,11. Every fast radio burst has a dispersion measurement, but none before now have had a redshift measurement, because of the difficulty in pinpointing their celestial coordinates. Here we report the discovery of a fast radio burst and the identification of a fading radio transient lasting ~6 days after the event, which we use to identify the host galaxy; we measure the galaxy’s redshift to be z = 0.492 ± 0.008. The dispersion measure and redshift, in combination, provide a direct measurement of the cosmic density of ionized baryons in the intergalactic medium of ΩIGM = 4.9 ± 1.3 per cent, in agreement with the expectation from the Wilkinson Microwave Anisotropy Probe12, and including all of the so-called ‘missing baryons’. The ~6-day radio transient is largely consistent with the radio afterglow of a short γ-ray burst13, and its existence and timescale do not support progenitor models such as giant pulses from pulsars, and supernovae. This contrasts with the interpretation8 of another recently discovered fast radio burst, suggesting that there are at least two classes of bursts.

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The Parkes radio telescope and the Australia Telescope Compact Array are part of the Australia Telescope National Facility, which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO) and used the gSTAR national facility at Swinburne University of Technology. Parts of this work are based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, the Murchison Radio-astronomy Observatory operated by CSIRO, the Giant Metrewave Radio Telescope (GMRT), which is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research, the Sardinia Radio Telescope as part of scientific commissioning of the telescope, and the 100-m telescope of the MPIfR at Effelsberg. We acknowledge the Wajarri Yamatji people as the traditional owners of the MWA Observatory site.

Author information


  1. Square Kilometre Array Organisation, Jodrell Bank Observatory, SK11 9DL, UK

    • E. F. Keane
  2. Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail H29, PO Box 218, Victoria 3122, Australia

    • E. F. Keane
    • , S. Bhandari
    • , E. Barr
    • , M. Caleb
    • , C. Flynn
    • , A. Jameson
    • , E. Petroff
    • , W. van Straten
    • , M. Bailes
    • , R. Allen
    •  & J. Cooke
  3. Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), Australia

    • E. F. Keane
    • , S. Bhandari
    • , N. D. R. Bhat
    • , M. Caleb
    • , C. Flynn
    • , A. Jameson
    • , E. Petroff
    • , M. Bailes
    • , J. Cooke
    • , S. J. Tingay
    •  & R. Wayth
  4. Commonwealth Science and Industrial Research Organisation (CSIRO), Astronomy and Space Science, Australia Telescope National Facility, PO Box 76, Epping, New South Wales 1710, Australia

    • S. Johnston
    •  & E. Petroff
  5. International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia 6102, Australia

    • N. D. R. Bhat
    • , S. J. Tingay
    • , A. Williams
    •  & R. Wayth
  6. Instituto Nazionale di Astrofisica (INAF)—Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (CA), Italy

    • M. Burgay
    • , A. Possenti
    •  & D. Perrodin
  7. Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australian Capital Territory 2611, Australia

    • M. Caleb
  8. Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, D-53121 Bonn, Germany

    • M. Kramer
    • , R. P. Eatough
    •  & M. Berezina
  9. Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK

    • M. Kramer
    • , B. W. Stappers
    •  & M. Mickaliger
  10. National Radio Astronomy Observatory, Socorro, New Mexico, USA

    • S. Burke-Spolaor
  11. Department of Astronomy, the University of Tokyo, Hongo, Tokyo 113-0033, Japan

    • T. Totani
    •  & S. Yamasaki
  12. National Astronomical Observatory of Japan, 2 Chome-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

    • M. Honma
    • , H. Furusawa
    •  & Y. Niino
  13. Department of Astronomical Science, SOKENDAI (Graduate University for the Advanced Study), Osawa, Mitaka 181-8588, Japan

    • M. Honma
  14. Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, Hawaii 96720, USA

    • T. Hattori
    •  & T. Terai
  15. Institute of Astronomy, Graduate School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan

    • T. Morokuma
  16. Kavli Institute for the Physics and Mathematics of the Universe (WPI), Institutes for Advanced Study, University of Tokyo, Kashiwa, Chiba 277-8583, Japan

    • T. Morokuma
    • , H. Sugai
    • , N. Tominaga
    •  & N. Yasuda
  17. Department of Physics, Faculty of Science and Engineering, Konan University, 8-9-1 Okamoto, Kobe, Hyogo 658-8501, Japan

    • N. Tominaga
  18. Cahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA

    • J. Jencson
    •  & M. M. Kasliwal
  19. Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201, USA

    • D. L. Kaplan
  20. National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune University Campus, Ganeshkhind, Pune 411 007, India

    • P. Chandra
  21. ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, The Netherlands

    • C. Bassa


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E.F.K. is the principal investigator of the SUPERB project, created SUPERB survey infrastructure at Parkes and Swinburne, led survey planning, formulated and wrote (with input from co-authors) the contents of this manuscript, performed the ΩIGM calculation, calculated the FRB spectral index, produced the FRB waterfall plot and the light curve plot. S.J. and S.B. performed ATCA observations and data analysis. S.J. and B.W.S. worked on radio light curve interpretation. S.B., N.D.R.B. and P.C. performed GMRT observations and data analysis. E.B. created survey infrastructure at Parkes and Swinburne and created the MWA shadowing infrastructure. Additionally, E.F.K., S.J., S.B., E.B., N.D.R.B., M. Burgay, M.C., C.F., M.K., E.P., A.P., W.v.S., M. Bailes., S.B.-S. and R.P.E. all performed observations for the SUPERB survey at Parkes. A.J. created and maintained the Parkes and Swinburne hardware and software infrastructure and performed data management for the SUPERB project. M. Bailes additionally provided Parkes and Swinburne hardware. C.F. and M.K. also worked on the calculation of the cosmic density of ionized baryons in the intergalactic medium. M.K. additionally performed FRB radio profile fitting. Polarization analysis of the FRB signal was performed by M.C., E.P. and W.v.S. W.v.S. also produced the polarization profile plot. E.P. additionally performed the Swift analysis. Non-imaging radio follow-up was performed by M. Burgay, A.P. and D.P. with the Sardinia Radio Telescope, by R.P.E. and M. Berezina with the Effelsberg Radio Telescope, and by B.W.S., M.M. and C.B. at the Lovell Telescope at Jodrell Bank. T. Totani, M.H., H.F., T.H., T.M., Y.N., H.S., T. Terai, N.T, S.Y. and N.Y. performed the Subaru observations. T. Totani, T.H., N.T. and S.Y. additionally performed Subaru data analysis, determined the spectral redshift and created the optical profile plot. C.F., T. Totani, S.Y. and R.A. performed the optical profile fitting. J.C. performed data analysis on the Keck and Subaru data, also obtained the spectral redshift and produced the optical spectrum plot. J.J. performed the Palomar observations. M.M.K. performed the Keck observation. MWA observations were performed by N.D.R.B., D.L.K., S.J.T., A.W. and R.W. with data analysis by D.L.K. and S.J.T. D.L.K. additionally measured the photometric redshift and produced the RGB (red–green–blue) image and photo-z plots (Extended Data Fig. 1).

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to E. F. Keane.

Extended data

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