Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin1,2,3. The only known repeating fast radio burst source4,5,6—FRB 121102—has been localized to a star-forming region in a dwarf galaxy7,8,9 at redshift 0.193 and is spatially coincident with a compact, persistent radio source7,10. The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. Here we report observations of FRB 121102 that show almost 100 per cent linearly polarized emission at a very high and variable Faraday rotation measure in the source frame (varying from +1.46 × 105 radians per square metre to +1.33 × 105 radians per square metre at epochs separated by seven months) and narrow (below 30 microseconds) temporal structure. The large and variable rotation measure demonstrates that FRB 121102 is in an extreme and dynamic magneto-ionic environment, and the short durations of the bursts suggest a neutron star origin. Such large rotation measures have hitherto been observed11,12 only in the vicinities of massive black holes (larger than about 10,000 solar masses). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole10. The bursts may therefore come from a neutron star in such an environment or could be explained by other models, such as a highly magnetized wind nebula13 or supernova remnant14 surrounding a young neutron star.

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We thank the staff of the Arecibo Observatory and the Green Bank Observatory for their help with our observations. We also thank B. Adebahr, L. Connor, G. Desvignes, R. Eatough, R. Fender, M. Haverkorn, A. Karastergiou, R. Morganti, E. Petroff, F. Vieyro and J. Weisberg for suggestions and comments on the manuscript. The Arecibo Observatory is operated by SRI International under a cooperative agreement with the National Science Foundation (AST-1100968), and in alliance with Ana G. Méndez-Universidad Metropolitana and the Universities Space Research Association. The Green Bank Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Breakthrough Listen (BL) is managed by the Breakthrough Initiatives, sponsored by the Breakthrough Prize Foundation (http://www.breakthroughinitiatives.org). The research leading to these results received funding from the European Research Council (ERC) under the European Union’s Seventh Framework Programme (FP7/2007-2013). J.W.T.H. is a Netherlands Organisation for Scientific Research (NWO) Vidi Fellow and, together with D.M., K.G. and C.G.B., acknowledges funding for this work from ERC Starting Grant DRAGNET under contract number 337062. L.G.S. acknowledges financial support from the ERC Starting Grant BEACON under contract number 279702, as well as the Max Planck Society. A.M.A. is an NWO Veni Fellow. S.C., J.M.C., P.D., T.J.W.L., M.A.M. and S.M.R. are partially supported by the NANOGrav Physics Frontiers Center (NSF award 1430284). V.M.K. holds the Lorne Trottier Chair in Astrophysics & Cosmology and a Canada Research Chair and receives support from an NSERC Discovery Grant and Herzberg Prize, from an R. Howard Webster Foundation Fellowship from the Canadian Institute for Advanced Research (CIFAR), and from the FRQNT Centre de Recherche en Astrophysique du Québec. C.J.L. acknowledges support from NSF award 1611606. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. B.M. acknowledges support from the Spanish Ministerio de Economía y Competitividad (MINECO) under grants AYA2016-76012-C3-1-P and MDM-2014-0369 of ICCUB (Unidad de Excelencia ‘María de Maeztu’). S.M.R. is a CIFAR Senior Fellow. P.S. holds a Covington Fellowship at DRAO.

Author information

Author notes

    • D. Michilli
    • , A. Seymour
    •  & J. W. T. Hessels

    These authors contributed equally to this work.


  1. ASTRON, Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands

    • D. Michilli
    • , J. W. T. Hessels
    • , A. M. Archibald
    • , E. A. K. Adams
    • , C. G. Bassa
    •  & N. Maddox
  2. Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

    • D. Michilli
    • , J. W. T. Hessels
    • , A. M. Archibald
    •  & K. Gourdji
  3. National Astronomy and Ionosphere Center, Arecibo Observatory, Puerto Rico 00612, USA

    • A. Seymour
    • , F. Fernandez
    •  & D. Whitlow
  4. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

    • L. G. Spitler
    •  & R. S. Wharton
  5. Space Science Laboratory, 7 Gauss Way, University of California, Berkeley, California 94710, USA

    • V. Gajjar
  6. Xinjiang Astronomical Observatory, CAS, 150 Science 1-Street, Urumqi, Xinjiang 830011, China

    • V. Gajjar
  7. Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008, China

    • V. Gajjar
  8. Academia Sinica Institute of Astronomy and Astrophysics, 645 N. A’ohoku Place, Hilo, Hawaii 96720, USA

    • G. C. Bower
  9. Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University, Ithaca, New York 14853, USA

    • S. Chatterjee
    •  & J. M. Cordes
  10. CSIRO Astronomy and Space Science, 26 Dick Perry Avenue, Kensington, Western Australia 6151, Australia

    • G. H. Heald
    •  & C. Sobey
  11. Department of Physics and McGill Space Institute, McGill University, 3600 University, Montréal, Quebec H3A 2T8, Canada

    • V. M. Kaspi
    •  & S. P. Tendulkar
  12. Department of Astronomy and Radio Astronomy Lab, University of California, Berkeley, California 94720, USA

    • C. J. Law
    • , G. Hellbourg
    •  & A. P. V. Siemion
  13. International Centre for Radio Astronomy Research - Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia

    • C. Sobey
  14. Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AA Groningen, The Netherlands

    • E. A. K. Adams
  15. Columbia Astrophysics Laboratory, Columbia University, New York, New York 10027, USA

    • S. Bogdanov
  16. Physics Department, University of Vermont, Burlington, Vermont 05401, USA

    • C. Brinkman
  17. National Radio Astronomy Observatory, PO Box O, Socorro, New Mexico 87801 USA

    • P. Demorest
  18. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA

    • T. J. W. Lazio
  19. Green Bank Observatory, PO Box 2, Green Bank, West Virginia 24944, USA

    • R. S. Lynch
  20. Center for Gravitational Waves and Cosmology, Chestnut Ridge Research Building, Morgantown, West Virginia 26505, USA

    • R. S. Lynch
    •  & M. A. McLaughlin
  21. Joint Institute for VLBI ERIC, Postbus 2, 7990 AA Dwingeloo, The Netherlands

    • B. Marcote
    •  & Z. Paragi
  22. Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, USA

    • M. A. McLaughlin
  23. National Radio Astronomy Observatory, Charlottesville, Virginia 22903, USA

    • S. M. Ransom
  24. National Research Council of Canada, Herzberg Astronomy and Astrophysics, Dominion Radio Astrophysical Observatory, PO Box 248, Penticton, British Columbia V2A 6J9, Canada

    • P. Scholz
  25. Radboud University, Nijmegen, Comeniuslaan 4, 6525 HP Nijmegen, The Netherlands

    • A. P. V. Siemion
  26. SETI Institute, 189 North Bernardo Avenue 200, Mountain View, California 94043, USA

    • A. P. V. Siemion
  27. Department of Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, Ohio 44106, USA

    • P. Van Rooy


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A.S. led the development of the Arecibo observing functionality used here and discovered the first bursts near 4.5 GHz. L.G.S. is Principal Investigator of the Arecibo monitoring campaign. D.M. discovered the rotation measure and analysed the burst properties in detail. K.G. searched all Arecibo datasets near 4.5 GHz for bursts. J.W.T.H. led the discussion on the interpretation of the results and writing of the manuscript. A.M.A. guided the development of the rotation measure fitting code. G.H.H. and C.S. performed the rotation measure synthesis and deconvolution analysis. G.C.B., S.C., J.M.C., V.G., V.M.K., C.J.L., M.A.M. and D.M. also contributed to the writing of the manuscript and analysis. V.G. observed, searched and detected bursts from the GBT at 6.5 GHz as a part of the BL monitoring campaign of known fast radio bursts. A.P.V.S. is the Principal Investigator of the BL project. C.B. helped with the polarization calibration of the test pulsar. G.H. wrote a code to splice raw voltages across computer nodes. All other co-authors contributed to the interpretation of the analysis results and to the final version of the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to J. W. T. Hessels.

Reviewer Information Nature thanks H. Falcke and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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