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  • Letter
  • Published:

High-energy emission from a magnetar giant flare in the Sculptor galaxy

Nature Astronomy volume 5, pages 385–391 (2021)Cite this article

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Abstract

Magnetars are the most highly magnetized neutron stars in the cosmos (with magnetic field 1013–1015 G). Giant flares from magnetars are rare, short-duration (about 0.1 s) bursts of hard X-rays and soft γ rays1,2. Owing to the limited sensitivity and energy coverage of previous telescopes, no magnetar giant flare has been detected at gigaelectronvolt (GeV) energies. Here, we report the discovery of GeV emission from a magnetar giant flare on 15 April 2020 (refs. 3,4 and A. J. Castro-Tirado et al., manuscript in preparation). The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope detected GeV γ rays from 19 s until 284 s after the initial detection of a signal in the megaelectronvolt (MeV) band. Our analysis shows that these γ rays are spatially associated with the nearby (3.5 megaparsecs) Sculptor galaxy and are unlikely to originate from a cosmological γ-ray burst. Thus, we infer that the γ rays originated with the magnetar giant flare in Sculptor. We suggest that the GeV signal is generated by an ultra-relativistic outflow that first radiates the prompt MeV-band photons, and then deposits its energy far from the stellar magnetosphere. After a propagation delay, the outflow interacts with environmental gas and produces shock waves that accelerate electrons to very high energies; these electrons then emit GeV γ rays as optically thin synchrotron radiation. This observation implies that a relativistic outflow is associated with the magnetar giant flare, and suggests the possibility that magnetars can power some short γ-ray bursts.

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Fig. 1: Map of the localization contour probability.

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Data availability

The Fermi-LAT data are publicly available at the Fermi Science Support Center website: https://fermi.gsfc.nasa.gov/ssc/. Filtered data supporting the findings of this study are available at https://www-glast.stanford.edu/pub_data/1801/.

Code availability

In this study we use the Fermi-LAT Science Tools, publicly available at the Fermi Science Support Center website: https://fermi.gsfc.nasa.gov/ssc/. The code required to reproduce each figure of the paper is available from the corresponding authors upon request.

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Acknowledgements

The Fermi-LAT Collaboration acknowledges support for LAT development, operation and data analysis from NASA and the Department of Energy (United States), CEA/Irfu and IN2P3/CNRS (France), ASI and INFN (Italy), MEXT, KEK and JAXA (Japan), and the K. A. Wallenberg Foundation, the Swedish Research Council and the National Space Board (Sweden). Science analysis support in the operations phase from INAF (Italy) and CNES (France) is also gratefully acknowledged. This work was performed in part under Department of Energy contract DE-AC02-76SF00515. E. Burns is a NASA Postdoctoral Program Fellow.

Author information

Authors and Affiliations

  1. Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC, USA

    M. Ajello

  2. Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA, USA

    W. B. Atwood & P. M. Saz Parkinson

  3. Department of Physics, Stockholm University, Stockholm, Sweden

    M. Axelsson

  4. Department of Physics, KTH Royal Institute of Technology, Stockholm, Sweden

    M. Axelsson & S. Larsson

  5. Università di Pisa and Istituto Nazionale di Fisica Nucleare, Pisa, Italy

    L. Baldini & A. Manfreda

  6. Istituto Nazionale di Fisica Nucleare, Trieste, Italy

    G. Barbiellini, F. Longo & M. Yassine

  7. Dipartimento di Fisica, Università di Trieste, Trieste, Italy

    G. Barbiellini, F. Longo & M. Yassine

  8. Department of Physics and Astronomy, Rice University, Houston, TX, USA

    M. G. Baring

  9. Istituto Nazionale di Fisica Nucleare, Padua, Italy

    D. Bastieri, S. Chen & R. Rando

  10. Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, Padua, Italy

    D. Bastieri & Z. Pei

  11. Istituto Nazionale di Fisica Nucleare, Pisa, Italy

    R. Bellazzini, M. Kuss, M. Pesce-Rollins, C. Sgrò & G. Spandre

  12. Dipartimento di Fisica, Università degli Studi di Perugia, Perugia, Italy

    A. Berretta, I. Mereu & G. Tosti

  13. Dipartimento di Fisica, “M. Merlin” dell’Università e del Politecnico di Bari, Bari, Italy

    E. Bissaldi, P. de la Torre Luque, L. Di Venere, P. Fusco, N. Giglietto, F. Giordano, F. Loparco, S. Rainò, D. Serini & P. Spinelli

  14. Istituto Nazionale di Fisica Nucleare, Bari, Italy

    E. Bissaldi, L. Di Venere, P. Fusco, F. Gargano, N. Giglietto, F. Giordano, F. Loparco, M. N. Mazziotta, S. Rainò & P. Spinelli

  15. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA, USA

    R. D. Blandford, R. A. Cameron, S. W. Digel, N. Di Lalla, P. F. Michelson, M. E. Monzani, I. V. Moskalenko, N. Omodei, E. Orlando, T. A. Porter, A. Reimer & H. Tajima

  16. Istituto Nazionale di Fisica Nucleare, Turin, Italy

    R. Bonino, F. de Palma, L. Latronico & S. Maldera

  17. Dipartimento di Fisica, Università degli Studi di Torino, Turin, Italy

    R. Bonino

  18. Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, Montpellier, France

    J. Bregeon, F. Piron & L. Scotton

  19. Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France

    P. Bruel & D. Horan

  20. Deutsches Elektronen Synchrotron (DESY), Zeuthen, Germany

    R. Buehler, J. Li & V. S. Paliya

  21. Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA, USA

    E. Burns

  22. NASA Goddard Space Flight Center, Greenbelt, MD, USA

    E. Burns, S. Griffin, S. Guiriec, E. Hays, J. E. McEnery, J. L. Racusin, B. Rani, D. Tak, E. Troja & Z. Wadiasingh

  23. Institut für Theoretische Physik and Astrophysik, Universität Würzburg, Würzburg, Germany

    S. Buson

  24. INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, Milan, Italy

    P. A. Caraveo & G. Chiaro

  25. Italian Space Agency, Rome, Italy

    E. Cavazzuti

  26. Department of Physics and Astronomy, University of Padova, Padua, Italy

    S. Chen & R. Rando

  27. Space Science Division, Naval Research Laboratory, Washington, DC, USA

    C. C. Cheung, M. Kerr & M. N. Lovellette

  28. Istituto Nazionale di Fisica Nucleare, Rome, Italy

    S. Ciprini & A. Morselli

  29. Space Science Data Center - Agenzia Spaziale Italiana, Rome, Italy

    S. Ciprini

  30. Department of Statistical Science, University of Padua, Padua, Italy

    D. Costantin

  31. Department of Astronomy, University of Maryland, College Park, MD, USA

    M. Crnogorcevic, J. E. McEnery & E. Troja

  32. Istituto Nazionale di Fisica Nucleare, Perugia, Italy

    S. Cutini, M. Kovačević, P. Lubrano, I. Mereu & G. Tosti

  33. INAF Istituto di Radioastronomia, Bologna, Italy

    F. D’Ammando, M. Giroletti, M. Orienti & G. Principe

  34. Department of Physics, University of Johannesburg, Johannesburg, South Africa

    F. Fana Dirirsa

  35. Department of Physical Sciences, Hiroshima University, Hiroshima, Japan

    Y. Fukazawa & H. Poon

  36. Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics, Erlangen, Germany

    S. Funk & A. Yusafzai

  37. Department of Physics, The George Washington University, Washington, DC, USA

    R. Gill & S. Guiriec

  38. Department of Natural Sciences, Open University of Israel, Ra’anana, Israel

    R. Gill & J. Granot

  39. Max-Planck-Institut für Physik, Munich, Germany

    D. Green, D. Paneque & M. N. Takahashi

  40. AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Gif-sur-Yvette, France

    I. A. Grenier

  41. Science Institute, University of Iceland, Reykjavik, Iceland

    G. Jóhannesson

  42. Nordita, Royal Institute of Technology and Stockholm University, Stockholm, Sweden

    G. Jóhannesson

  43. The Oskar Klein Centre for Cosmoparticle Physics, Stockholm, Sweden

    S. Larsson

  44. School of Education, Health and Social Studies, Natural Science, Dalarna University, Falun, Sweden

    S. Larsson

  45. Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität Innsbruck, Innsbruck, Austria

    G. Martí-Devesa, A. Reimer & O. Reimer

  46. Hiroshima Astrophysical Science Center, Hiroshima University, Hiroshima, Japan

    T. Mizuno

  47. Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center, Greenbelt, MD, USA

    M. Negro

  48. Department of Physics and Center for Space Sciences and Technology, University of Maryland, Baltimore, MD, USA

    M. Negro

  49. Istituto Nazionale di Fisica Nucleare, and Università di Trieste, Trieste, Italy

    E. Orlando & G. Zaharijas

  50. Center for Space Studies and Activities “G. Colombo”, University of Padova, Padua, Italy

    R. Rando

  51. Korea Astronomy and Space Science Institute, Daejeon, Korea

    B. Rani

  52. Centre for Astro-Particle Physics (CAPP) and Department of Physics, University of Johannesburg, Johannesburg, South Africa

    S. Razzaque

  53. Department of Physics, The University of Hong Kong, Hong Kong, China

    P. M. Saz Parkinson

  54. Laboratory for Space Research, The University of Hong Kong, Hong Kong, China

    P. M. Saz Parkinson

  55. Space Sciences Division, NASA Ames Research Center, Moffett Field, CA, USA

    J. D. Scargle

  56. NYCB Real-Time Computing Inc., Lattingtown, NY, USA

    E. J. Siskind

  57. Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan

    H. Tajima

  58. Department of Physics, University of Maryland, College Park, MD, USA

    D. Tak

  59. Institute of Space Sciences (CSICIEEC), Barcelona, Spain

    D. F. Torres

  60. Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain

    D. F. Torres

  61. Praxis Inc., Alexandria, VA, USA; resident at Naval Research Laboratory, Washington, DC, USA

    K. Wood

  62. Center for Astrophysics and Cosmology, University of Nova Gorica, Nova Gorica, Slovenia

    G. Zaharijas

Consortia

The Fermi-LAT Collaboration

  • M. Ajello
  • , W. B. Atwood
  • , M. Axelsson
  • , L. Baldini
  • , G. Barbiellini
  • , M. G. Baring
  • , D. Bastieri
  • , R. Bellazzini
  • , A. Berretta
  • , E. Bissaldi
  • , R. D. Blandford
  • , R. Bonino
  • , J. Bregeon
  • , P. Bruel
  • , R. Buehler
  • , E. Burns
  • , S. Buson
  • , R. A. Cameron
  • , P. A. Caraveo
  • , E. Cavazzuti
  • , S. Chen
  • , C. C. Cheung
  • , G. Chiaro
  • , S. Ciprini
  • , D. Costantin
  • , M. Crnogorcevic
  • , S. Cutini
  • , F. D’Ammando
  • , P. de la Torre Luque
  • , F. de Palma
  • , S. W. Digel
  • , N. Di Lalla
  • , L. Di Venere
  • , F. Fana Dirirsa
  • , Y. Fukazawa
  • , S. Funk
  • , P. Fusco
  • , F. Gargano
  • , N. Giglietto
  • , R. Gill
  • , F. Giordano
  • , M. Giroletti
  • , J. Granot
  • , D. Green
  • , I. A. Grenier
  • , S. Griffin
  • , S. Guiriec
  • , E. Hays
  • , D. Horan
  • , G. Jóhannesson
  • , M. Kerr
  • , M. Kovačević
  • , M. Kuss
  • , S. Larsson
  • , L. Latronico
  • , J. Li
  • , F. Longo
  • , F. Loparco
  • , M. N. Lovellette
  • , P. Lubrano
  • , S. Maldera
  • , A. Manfreda
  • , G. Martí-Devesa
  • , M. N. Mazziotta
  • , J. E. McEnery
  • , I. Mereu
  • , P. F. Michelson
  • , T. Mizuno
  • , M. E. Monzani
  • , A. Morselli
  • , I. V. Moskalenko
  • , M. Negro
  • , N. Omodei
  • , M. Orienti
  • , E. Orlando
  • , V. S. Paliya
  • , D. Paneque
  • , Z. Pei
  • , M. Pesce-Rollins
  • , F. Piron
  • , H. Poon
  • , T. A. Porter
  • , G. Principe
  • , J. L. Racusin
  • , S. Rainò
  • , R. Rando
  • , B. Rani
  • , S. Razzaque
  • , A. Reimer
  • , O. Reimer
  • , P. M. Saz Parkinson
  • , J. D. Scargle
  • , L. Scotton
  • , D. Serini
  • , C. Sgrò
  • , E. J. Siskind
  • , G. Spandre
  • , P. Spinelli
  • , H. Tajima
  • , M. N. Takahashi
  • , D. Tak
  • , D. F. Torres
  • , G. Tosti
  • , E. Troja
  • , Z. Wadiasingh
  • , K. Wood
  • , M. Yassine
  • , A. Yusafzai
  •  & G. Zaharijas

Contributions

The Fermi-LAT was designed and constructed by the Fermi-LAT Collaboration. The operation, data processing, calibration, Monte Carlo simulations of the detector and of theoretical models, and data analyses were performed by the members of the Fermi-LAT Collaboration. All Fermi-LAT collaborators that signed this paper contributed to the editing of and comments on the final version of the manuscript. A.B., N. Di Lalla, N.O. and F.P. contributed to the analysis and the writing of the manuscript and S. Razzaque provided the interpretation and contributed to the writing of the paper.

Corresponding authors

Correspondence to A. Berretta, N. Di Lalla, N. Omodei, F. Piron or S. Razzaque.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

Peer review information Nature Astronomy thanks the anonymous reviewers for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Best-fit parameters from the LAT unbinned likelihood analysis.

All fluxes are calculated in the 100 MeV to 10 GeV energy range.

Extended Data Fig. 2 List of selected events.

We highlight those with high probability (>90%) to be associated with the LAT-detected source, according to the likelihood analysis. The uncertainty on the estimated γ-ray energies is of the order of 10%. The last two columns show the angular distance to the centre of NGC 253 (the Sculptor galaxy) and the 68% containment radius of the PSF.

Extended Data Fig. 3 Distribution of likelihood ratio (LR) values.

LR values for 105 simulated ROIs using the standard Rayleigh formula (a) and using the TS map to compute the probability (b). The red distributions correspond to the point source hypothesis, while the blue distributions take into account of the galaxy extension. The step in the distributions at low LR is due to many low-LR trials occupying the first bin. The values of the LRs associated with the Sculptor galaxy are highlighted by red and blue vertical dashed lines for the two cases.

Extended Data Fig. 4 Association probability and false alarm rate.

Summary of the probability for a random association with the Sculptor galaxy and with the GRB 200415A.

Extended Data Fig. 5 Triplet distribution.

Distribution of the time intervals Δt for triplets formed by three consecutive photons with (green) and without (dashed red) taking into account the correction for the effects of the LAT orbit and FOV. The expected distribution in case of independent events is represented as a solid black line. The vertical line in blue shows the period of the Fermi orbit (5,790 s), while the yellow vertical line indicates Δt = 264.87 s corresponding to the photon triplet detected by the LAT after GBM detected emission from GRB 200415A.

Extended Data Fig. 6 Rate and exposure as a function of time.

Bayesian blocks representation of the arrival times of the γ rays with the prior parameter p = 3 (red). Light green and dark gray are the daily and weekly count rates, while the blue curve shows the weekly-averaged exposure (between 100 MeV and 300 GeV, assuming a power-law photon index of −2) for a 1°-radius ROI in the direction of Sculptor for the entire time of the mission. Values of the exposure, in units of 108 cm2 s, can be read from the right y-axis. The three yellow bands highlight three characteristic observing profiles: 35° rocking angle, at the beginning of the mission, an observation strategy favouring the Galactic Centre region, in the middle, and, lastly, the period between the start of the solar drive anomaly and the implementation of a reoptimized survey strategy.

Extended Data Fig. 7 Comparison with the second Fermi-LAT GRB catalogue.

a, Onset times (TLAT,0 ) in the 100 MeV–100 GeV band versus the end of the GRB as detected by GBM in the 50–300 keV energy range (TGBM,95 ). b, Durations (TLAT,100 ) calculated in the 100 MeV–100 GeV energy range versus the same quantities calculated in the 50–300 keV energy range (TGBM,90 ). The solid line denotes where the two values are equal. Empty Blue and filled red circles represent long and short GRBs, respectively (data from 2FLGC27]). GRB 200415A is added and marked with a yellow star. The two SGRBs 160702A and GRB 170127C from 2FLGC, which exhibit similar durations, are highlighted with a magenta circle and green square, respectively.

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The Fermi-LAT Collaboration. High-energy emission from a magnetar giant flare in the Sculptor galaxy. Nat Astron 5, 385–391 (2021). https://doi.org/10.1038/s41550-020-01287-8

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