The host galaxy of a fast radio burst

Observations of a six-day-long radio transient following a fast radio burst have yielded the host galaxy’s redshift, which, combined with the dispersion measure, provides a direct measurement of the cosmic density of ionized baryons in the intergalactic medium including all of the so-called ‘missing baryons’. A fast radio burst located This paper reports the discovery, with the Parkes radio telescope, of a fast radio burst, FRB 150418. A multi-wavelength multi-telescope follow-up study detected a radio transient two hours after the initial burst, lasting about six days before fading to a quiescent level. The authors interpret this fading source as the afterglow of the FRB. Fast radio bursts are transient radio pulses lasting only a few milliseconds and previously it has not been possible to localize such a burst and determine a redshift. The source of FRB 150418 is identified as an elliptical galaxy with redshift of 0.492. In recent years, millisecond-duration radio signals originating in distant galaxies appear to have been discovered in the so-called fast radio bursts 1 , 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 investigations 10 , 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 Ω IGM = 4.9 ± 1.3 per cent, in agreement with the expectation from the Wilkinson Microwave Anisotropy Probe 12 , 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 burst 13 , and its existence and timescale do not support progenitor models such as giant pulses from pulsars, and supernovae. This contrasts with the interpretation 8 of another recently discovered fast radio burst, suggesting that there are at least two classes of bursts.