Effects of Fallback Accretion on Protomagnetar Outflows in Gamma-Ray Bursts and Superluminous Supernovae

Brian D. Metzger, Paz Beniamini, Dimitrios Giannios

Research output: Contribution to journalArticlepeer-review


Rapidly spinning, strongly magnetized protoneutron stars ("millisecond protomagnetars") are candidate central engines of long-duration gamma-ray bursts (GRBs), superluminous supernovae (SLSNe), and binary neutron star mergers. Magnetar birth may be accompanied by the fallback of stellar debris, lasting for seconds or longer following the explosion. Accretion alters the magnetar evolution by (1) providing an additional source of rotational energy (or a potential sink, if the propeller mechanism operates), (2) enhancing the spin-down luminosity above the dipole rate by compressing the magnetosphere and expanding the polar cap region of open magnetic field lines, and (3) supplying an additional accretion-powered neutrino luminosity that sustains the wind baryon loading, even after the magnetar's internal neutrino luminosity has subsided. The more complex evolution of the jet power and magnetization of an accreting magnetar more readily accounts for the high 56Ni yields of GRB SNe and the irregular time evolution of some GRB light curves (e.g., bursts with precursors followed by a long quiescent interval before the main emission episode). Additional baryon loading from accretion-powered neutrino irradiation of the polar cap lengthens the time frame over which the jet magnetization is in the requisite range σ ≲ 103 for efficient gamma-ray emission, thereby accommodating GRBs with ultralong durations. Though accretion does not significantly raise the maximum energy budget from the limit of ≲ few × 1052 erg for an isolated magnetar, it greatly expands the range of magnetic field strengths and birth spin periods capable of powering GRB jets, reducing the differences between the magnetar properties normally invoked to explain GRBs versus SLSNe.

Original languageEnglish
Article number95
JournalAstrophysical Journal
Issue number2
StatePublished - 20 Apr 2018
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.


  • accretion, accretion disks
  • gamma-ray burst: general
  • stars: jets
  • stars: magnetars
  • supernovae: general


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