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Magnetic energy dissipation and gamma-ray emission in energetic pulsars

Presentation #116.33 in the session Stellar/Compact Objects.

Published onJul 01, 2023
Magnetic energy dissipation and gamma-ray emission in energetic pulsars

Some of the most energetic pulsars exhibit rotation-modulated gamma-ray emission in the 0.1 to 100 GeV band. The luminosity of this emission is typically 0.1-10% of the pulsar spin-down power (gamma-ray efficiency), implying that a significant fraction of the available electromagnetic energy is dissipated in the magnetosphere and reradiated as high-energy photons. To investigate this phenomenon we model a pulsar magnetosphere using 3D particle-in-cell simulations with strong synchrotron cooling. We particularly focus on the dynamics of the equatorial current sheet where magnetic reconnection and energy dissipation take place. Our simulations demonstrate that a fraction of the spin-down power dissipated in the magnetospheric current sheet is controlled by reconnection at microphysical plasma scales and only depends on the pulsar inclination angle. We demonstrate that the maximum energy and the distribution function of accelerated pairs is controlled by the available magnetic energy per particle near the current sheet, the magnetization parameter. The shape and the extent of the plasma distribution is imprinted in the observed synchrotron emission, in particular, the peak of the observed spectrum and the cutoff. We study how the strength of synchrotron cooling affects the observed variety of spectral shapes. Our conclusions naturally explain why pulsars with higher spin-down power have wider spectral shapes and, as a result, lower gamma-ray efficiency.

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