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Abstract We investigate how a fast radio burst (FRB) emitted near a magnetar would propagate through its surrounding dipole magnetosphere at radiir= 107–109cm. First, we show that a GHz burst emitted in the O-mode with luminosityL≫ 1040erg s−1is immediately damped for all propagation directions except a narrow cone along the magnetic axis. Then, we examine bursts in the X-mode. GHz waves propagating near the magnetic equator behave as magnetohydrodynamic (MHD) waves if they haveL≫ 1040erg s−1. The waves develop plasma shocks in each oscillation and dissipate at cm. Waves with lowerLor propagation directions closer to the magnetic axis do not obey MHD. Instead, they interact with individual particles and require a kinetic description. The kinetic interaction quickly accelerates particles to Lorentz factors 104–105at the expense of the wave energy, which again results in strong damping of the wave. In either propagation regime, MHD or kinetic, the dipole magnetosphere surrounding the FRB source acts as a pillow absorbing the radio burst and reradiating the absorbed energy in X-rays. These results constrain the origin of observed FRBs. We argue that the observed FRBs avoid damping because they are emitted by relativistic outflows from magnetospheric explosions, so that the GHz waves do not need to propagate through the outer equilibrium magnetosphere surrounding the magnetar.
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Can a Strong Radio Burst Escape the Magnetosphere of a Magnetar?
Abstract We examine the possibility that fast radio bursts (FRBs) are emitted inside the magnetosphere of a magnetar. On its way out, the radio wave must interact with a low-densitye±plasma in the outer magnetosphere at radiiR= 109–1010cm. In this region, the magnetospheric particles have a huge cross section for scattering the wave. As a result, the wave strongly interacts with the magnetosphere and compresses it, depositing the FRB energy into the compressed field and the scattered radiation. The scattered spectrum extends to theγ-ray band and triggerse±avalanche, further boosting the opacity. These processes choke FRBs, disfavoring scenarios with a radio source confined atR≪ 1010cm. Observed FRBs can be emitted by magnetospheric flare ejecta transporting energy to large radii.
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- Award ID(s):
- 2009453
- PAR ID:
- 10305468
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 922
- Issue:
- 1
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L7
- Size(s):
- Article No. L7
- Sponsoring Org:
- National Science Foundation
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