A direct localization of a fast radio burst and its host

Journal name:
Nature
Volume:
541,
Pages:
58–61
Date published:
DOI:
doi:10.1038/nature20797
Received
Accepted
Published online

Fast radio bursts1, 2 are astronomical radio flashes of unknown physical nature with durations of milliseconds. Their dispersive arrival times suggest an extragalactic origin and imply radio luminosities that are orders of magnitude larger than those of all known short-duration radio transients3. So far all fast radio bursts have been detected with large single-dish telescopes with arcminute localizations, and attempts to identify their counterparts (source or host galaxy) have relied on the contemporaneous variability of field sources4 or the presence of peculiar field stars5 or galaxies4. These attempts have not resulted in an unambiguous association6, 7 with a host or multi-wavelength counterpart. Here we report the subarcsecond localization of the fast radio burst FRB 121102, the only known repeating burst source8, 9, 10, 11, using high-time-resolution radio interferometric observations that directly image the bursts. Our precise localization reveals that FRB 121102 originates within 100 milliarcseconds of a faint 180-microJansky persistent radio source with a continuum spectrum that is consistent with non-thermal emission, and a faint (twenty-fifth magnitude) optical counterpart. The flux density of the persistent radio source varies by around ten per cent on day timescales, and very long baseline radio interferometry yields an angular size of less than 1.7 milliarcseconds. Our observations are inconsistent with the fast radio burst having a Galactic origin or its source being located within a prominent star-forming galaxy. Instead, the source appears to be co-located with a low-luminosity active galactic nucleus or a previously unknown type of extragalactic source. Localization and identification of a host or counterpart has been essential to understanding the origins and physics of other kinds of transient events, including gamma-ray bursts12, 13 and tidal disruption events14. However, if other fast radio bursts have similarly faint radio and optical counterparts, our findings imply that direct subarcsecond localizations may be the only way to provide reliable associations.

At a glance

Figures

  1. VLA detection of FRB 121102.
    Figure 1: VLA detection of FRB 121102.

    a, A 5-ms dispersion-corrected dirty image showing a burst from FRB 121102 at MJD 57633.67986367 (2016 September 2). The approximate localization uncertainty from previous Arecibo detections9 (3′ beam full-width at half-maximum (FWHM)) is shown with overlapping circles. b, A zoomed-in portion of a, deconvolved and re-centred on the detection, showing the approximately 0.1″ localization of the burst. c, Time–frequency data extracted from phased VLA visibilities at the burst location shows the ν−2 dispersive sweep of the burst. The solid black lines illustrate the expected sweep for DM = 558 pc cm−3. The de-dispersed lightcurve and spectra are projected to the upper and right panels, respectively. In all panels, the colour scale indicates the flux density.

  2. Radio and optical images of the FRB 121102 field.
    Figure 2: Radio and optical images of the FRB 121102 field.

    a, VLA image at 3 GHz with a combination of array configurations. The image resolution is 2″ and the r.m.s. is σ = 2 μJy per beam. The Arecibo detection9 uncertainty regions (3′ beam FWHM) are indicated with overlapping white circles. The radio counterpart of the bursts detected at the VLA is highlighted by a 20″ white square within the overlap region. The colour scale indicates the observed flux density. Inset, Gemini r-band image of the 20″ square shows an optical counterpart (rAB = 25.1 ± 0.1 mag), as identified by the 5″ bars. b, The light curve of the persistent radio source coincident with FRB 121102 over the course of the VLA campaign, indicating variability on timescales shorter than 1 day. Error bars are 1σ. The average flux density of the source of about 180 μJy is marked in grey, and the epochs at which bursts were detected at the VLA are indicated (red triangles). The variability of the persistent radio counterpart is uncorrelated with the detection of bursts (see Methods).

  3. Broadband spectral energy distribution of the counterpart.
    Figure 3: Broadband spectral energy distribution of the counterpart.

    Detections of the persistent radio source (blue circles), the optical counterpart (red and orange squares) and 5σ upper limits at various frequency bands (arrows) are shown; see Methods for details. Spectral energy distributions of other radio point sources are scaled to match the radio flux density at 10 GHz and overlaid for comparison: low-luminosity AGN in Henize 2-10, a star-forming dwarf galaxy28 placed at 25 Mpc (blue); radio-loud AGN QSO 2128−12329 scaled by 10−4.3 to simulate a lower-luminosity AGN and placed at 3 Gpc (yellow); and the Crab nebula30 at 4 Mpc (red). Fν is the flux density and νFν is the flux density weighted by photon energy.

  4. The offset of FRB 121102 from the persistent counterpart.
    Extended Data Fig. 1: The offset of FRB 121102 from the persistent counterpart.

    Five bursts detected at the VLA with the highest resolution (A-array, 3 GHz) are plotted (crosses), with epoch indicated by MJD values. The (right ascension (RA), declination (Dec)) coordinate difference (burst relative to counterpart) is shown with an ellipse indicating the 1σ error calculated as the quadrature sum of errors in the two sources. VLBA and EVN positions are indicated, with 1σ errors smaller than the symbols. The centroid of the Gemini optical counterpart is shown (red dot) with an estimated 1σ error circle of 100 mas (red) from fitting and radio-optical frame tie uncertainties.

  5. VLA spectrum of the persistent counterpart to FRB 121102.
    Extended Data Fig. 2: VLA spectrum of the persistent counterpart to FRB 121102.

    The integrated flux density Fν is plotted for each epoch of observation (listed by MJD) over a frequency range ν from 1 GHz to 25 GHz. Error bars represent 1σ uncertainties. The spectrum is non-thermal and inconsistent with a single power law.

Tables

  1. VLA detections of bursts from FRB 121102 and Arecibo constraints
    Extended Data Table 1: VLA detections of bursts from FRB 121102 and Arecibo constraints
  2. VLA 3-GHz observations of the persistent counterpart to FRB 121102 over time
    Extended Data Table 2: VLA 3-GHz observations of the persistent counterpart to FRB 121102 over time
  3. Flux density and position measurements of the persistent counterpart to FRB 121102
    Extended Data Table 3: Flux density and position measurements of the persistent counterpart to FRB 121102

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Author information

Affiliations

  1. Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University, Ithaca, New York 14853, USA

    • S. Chatterjee,
    • R. S. Wharton &
    • J. M. Cordes
  2. Department of Astronomy and Radio Astronomy Lab, University of California, Berkeley, California 94720, USA

    • C. J. Law
  3. National Radio Astronomy Observatory, Socorro, New Mexico 87801, USA

    • S. Burke-Spolaor,
    • P. Demorest &
    • B. J. Butler
  4. Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, USA

    • S. Burke-Spolaor &
    • M. A. McLaughlin
  5. Center for Gravitational Waves and Cosmology, West Virginia University, Chestnut Ridge Research Building, Morgantown, West Virginia 26505, USA

    • S. Burke-Spolaor &
    • M. A. McLaughlin
  6. ASTRON, Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands

    • J. W. T. Hessels &
    • C. G. Bassa
  7. Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

    • J. W. T. Hessels
  8. Academia Sinica Institute of Astronomy and Astrophysics, 645 North A’ohoku Place, Hilo, Hawaii 96720, USA

    • G. C. Bower
  9. Department of Physics and McGill Space Institute, McGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada

    • S. P. Tendulkar &
    • V. M. Kaspi
  10. Arecibo Observatory, HC3 Box 53995, Arecibo, Puerto Rico 00612, USA

    • A. Seymour
  11. National Research Council of Canada, Herzberg Astronomy and Astrophysics, Dominion Radio Astrophysical Observatory, PO Box 248, Penticton, British Columbia V2A 6J9, Canada

    • P. Scholz &
    • M. Rupen
  12. Haverford College, 370 Lancaster Avenue, Haverford, Pennsylvania 19041, USA

    • M. W. Abruzzo
  13. Columbia Astrophysics Laboratory, Columbia University, New York, New York 10027, USA

    • S. Bogdanov
  14. Joint Institute for VLBI ERIC, Postbus 2, 7990 AA Dwingeloo, The Netherlands

    • A. Keimpema,
    • B. Marcote,
    • Z. Paragi &
    • H. J. van Langevelde
  15. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA

    • T. J. W. Lazio
  16. National Radio Astronomy Observatory, Charlottesville, Virginia 22903, USA

    • S. M. Ransom
  17. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, Bonn D-53121, Germany

    • L. G. Spitler
  18. Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands

    • H. J. van Langevelde

Contributions

S.C. was principal investigator of the localization campaign described here. C.J.L. and S.B.-S. are principal investigators of the realfast project and performed the analysis that achieved the first VLA burst detections. S.C., C.J.L., R.S.W., S.B.-S., G.C.B., B.B. and P.D. performed detailed analysis of the VLA data. S.B.-S. and B.B. led the analysis of the VLA multi-band spectral data. J.W.T.H. was principal investigator of the EVN observations, which were analysed by Z.P. and B.M. G.C.B. was principal investigator of the VLBA observations, and led their analysis. J.W.T.H., A.S. and L.G.S. led the execution and analysis of the parallel Arecibo observing campaign. P.D. led the commissioning of fast-sampled VLA observing modes. S.C. was principal investigator of the ALMA observations. P.S. was principal investigator of the X-ray observations, and performed the X-ray analysis, along with S.B. S.P.T. was principal investigator of the Gemini observations, and along with C.G.B. led the analysis of Keck, Gemini and archival UKIDSS and GLIMPSE data. S.C. and C.J.L. led the writing of the manuscript, with substantial contributions from J.M.C. and J.W.T.H. All authors contributed substantially to the interpretation of the analysis results and to the final version of the manuscript.

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to:

Reviewer Information Nature thanks H. Falcke and G. Hallinan for their contribution to the peer review of this work.

Author details

Extended data figures and tables

Extended Data Figures

  1. Extended Data Figure 1: The offset of FRB 121102 from the persistent counterpart. (192 KB)

    Five bursts detected at the VLA with the highest resolution (A-array, 3 GHz) are plotted (crosses), with epoch indicated by MJD values. The (right ascension (RA), declination (Dec)) coordinate difference (burst relative to counterpart) is shown with an ellipse indicating the 1σ error calculated as the quadrature sum of errors in the two sources. VLBA and EVN positions are indicated, with 1σ errors smaller than the symbols. The centroid of the Gemini optical counterpart is shown (red dot) with an estimated 1σ error circle of 100 mas (red) from fitting and radio-optical frame tie uncertainties.

  2. Extended Data Figure 2: VLA spectrum of the persistent counterpart to FRB 121102. (83 KB)

    The integrated flux density Fν is plotted for each epoch of observation (listed by MJD) over a frequency range ν from 1 GHz to 25 GHz. Error bars represent 1σ uncertainties. The spectrum is non-thermal and inconsistent with a single power law.

Extended Data Tables

  1. Extended Data Table 1: VLA detections of bursts from FRB 121102 and Arecibo constraints (164 KB)
  2. Extended Data Table 2: VLA 3-GHz observations of the persistent counterpart to FRB 121102 over time (659 KB)
  3. Extended Data Table 3: Flux density and position measurements of the persistent counterpart to FRB 121102 (161 KB)

Supplementary information

PDF files

  1. Supplementary Information (62 KB)

    This file contains extended acknowledgements.

Additional data