Corona of Magnetars

By A. Beloborodov, C. Thompson. 2006

283 citations recorded by the source corpus.

We develop a theoretical model that explains the formation of hot coronae around strongly magnetized neutron stars—magnetars. The starquakes of a magnetar shear its external magnetic field, which becomes nonpotential and threaded by an electric current. Once twisted, the magnetosphere cannot untwist immediately because of its self-induction. The self-induction electric field lifts particles from the stellar surface, accelerates them, and initiates avalanches of pair creation in the magnetosphere. The created plasma corona maintains the electric current demanded by 𝛁 × and regulates the self-induction EMF by screening. This corona persists in dynamic equilibrium: it is continually lost to the stellar surface on the light crossing time ~10-4 s and replenished with new particles. In essence, the twisted magnetosphere acts as an accelerator that converts the toroidal field energy to particle kinetic energy. Using a direct numerical experiment, we show that the corona self-organizes quickly (on a millisecond timescale) into a quasi-steady state, with voltage 108-109 V along the magnetic lines. The voltage is maintained near the threshold for e± discharge. The heating rate of the corona is ~1036 ergs s-1, in agreement with the observed persistent, high-energy output of magnetars. We deduce that a static twist that is suddenly implanted into the magnetosphere will decay on a timescale of 1-10 yr. The particles accelerated in the corona impact the solid crust, knock out protons, and regulate the column density of the hydrostatic atmosphere of the star. The transition layer between the atmosphere and corona may be hot enough to create additional e± pairs. This layer can be the source of the observed 100 keV emission from magnetars. The corona emits curvature radiation and can supply the observed IR-optical luminosity.

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/7a1bedbcc3afeac57861ef3ed31442c61eefc221

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Citations in the corpus

THE NUCLEAR SPECTROSCOPIC TELESCOPE ARRAY (NuSTAR) HIGH-ENERGY X-RAY MISSION (2013, background): “This emission is both unpredicted and not understood, though some models have been suggested (e.g., Heyl & Hernquist 2005; Baring & Harding 2007; Beloborodov & Thompson 2007; Beloborodov 2012) and some intriguing correlations noted (Kaspi & Boydstun 2010; Enoto et al. 2011).”
1E 1547.0–5408: A Radio-emitting Magnetar with a Rotation Period of 2 Seconds (2007, background): “Closed, twisted field lines may span a large range of azimuthal angles near the surface of the neutron star, and models of pair production there yield relativistic that are appropriate3g ∼ 10 for radio emission (Beloborodov & Thompson 2007).”
A model for fast extragalactic radio bursts (2014, background): “At the quiescent state, the magnetar magnetosphere is filled by electron-positron plasma generated in cascades induced near the surface of the star by slow untwisting of magnetospheric field lines (Thompson et al. 2002; Beloborodov & Thompson 2007; Thompson 2008; Beloborodov 2013a).”
Time-dependent pair cascades in magnetospheres of neutron stars - I. Dynamics of the polar cap cascade with no particle supply from the neutron star surface (2010, background): “Electromagnetically driven cascades should generate plasma in magnetospheres of magnetars along open (Thompson 2008) as well as closed magnetic field lines (Beloborodov & Thompson 2007).”
Coherent emission mechanisms in astrophysical plasmas (2017, background): “Quasi-stationary gaps are unstable, and E‖ 6= 0 is more plausibly described in terms of large-amplitude electrostatic oscillations (Levinson et al, 2005; Beloborodov and Thompson, 2007) propagating outwards (Luo and Melrose, 2008).”