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Implications of a Fast Radio Burst from a Galactic Magnetar

Margalit, Ben and Beniamini, Paz and Sridhar, Navin and Metzger, Brian D. (2020) Implications of a Fast Radio Burst from a Galactic Magnetar. Astrophysical Journal Letters, 899 (2). Art. No. L27. ISSN 2041-8213.

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A luminous radio burst was recently detected in temporal coincidence with a hard X-ray flare from the Galactic magnetar SGR 1935+2154 with a time and frequency structure consistent with cosmological fast radio bursts (FRBs) and a fluence within a factor of 10 of the least energetic extragalactic FRB previously detected. Although active magnetars are commonly invoked FRB sources, several distinct mechanisms have been proposed for generating the radio emission that make different predictions for the accompanying higher-frequency radiation. We show that the properties of the coincident radio and X-ray flares from SGR 1935+2154, including their approximate simultaneity and relative fluence E_(radio)/E-X ~ 10⁻⁵, as well as the duration and spectrum of the X-ray emission, are consistent with extant predictions for the synchrotron maser shock model. Rather than arising from the inner magnetosphere, the X-rays are generated by (incoherent) synchrotron radiation from thermal electrons heated at the same internal shocks that produce the coherent maser emission as ultrarelativistic flare ejecta collides with a slower particle outflow (e.g., as generated by earlier flaring activity) on a radial scale of cm. Although the rate of SGR 1935+2154–like bursts in the local universe is not sufficient to contribute appreciably to the extragalactic FRB rate, the inclusion of an additional population of more active magnetars with stronger magnetic fields than the Galactic population can explain both the FRB rate and the repeating fraction, but only if the population of active magnetars are born at a rate that is at least 2 orders of magnitude lower than that of the SGR 1935+2154–like magnetars. This may imply that the more active magnetar sources are not younger magnetars formed in a similar way to the Milky Way population (e.g., via ordinary supernovae) but are instead formed through more exotic channels, such as superluminous supernovae, accretion-induced collapse, or neutron star mergers.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Margalit, Ben0000-0001-8405-2649
Beniamini, Paz0000-0001-7833-1043
Sridhar, Navin0000-0002-5519-9550
Metzger, Brian D.0000-0002-4670-7509
Additional Information:© 2020 The American Astronomical Society. Received 2020 May 16; revised 2020 July 23; accepted 2020 August 5; published 2020 August 19. We thank Bryan Gaensler and George Younes for helpful insight. B.M. is supported by NASA through NASA Hubble Fellowship grant No. HST-HF2-51412.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS5-26555. The research of P.B. was funded by the Gordon and Betty Moore Foundation through grant GBMF5076. N.S. is supported by the Columbia University Dean's fellowship and through the National Science Foundation (grant No. 80NSSC18K1104). B.D.M. is supported in part by the Simons Foundation through the Simons Fellowship Program in Mathematics and Physics (grant No. 606260).
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF2-51412.001-A
Gordon and Betty Moore FoundationGBMF5076
Columbia UniversityUNSPECIFIED
Simons Foundation606260
NASA Einstein FellowshipUNSPECIFIED
Subject Keywords:Radio transient sources ; Magnetars ; Soft gamma-ray repeaters
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Radio transient sources (2008); Magnetars (992); Soft gamma-ray repeaters (1471)
Record Number:CaltechAUTHORS:20200821-093503887
Persistent URL:
Official Citation:Ben Margalit et al 2020 ApJL 899 L27
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105058
Deposited By: Tony Diaz
Deposited On:21 Aug 2020 17:08
Last Modified:21 Aug 2020 17:08

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