Magnetic dissipation in the Crab Nebula

TL;DR

This paper investigates magnetic dissipation in the Crab Nebula, analyzing observational data to understand the nebula's magnetic properties and dissipation timescales, with implications for pulsar wind models and nebula energetics.

Contribution

It provides constraints on the magnetic inclination angle and dissipation timescale in the Crab Nebula, challenging existing models and highlighting the need for efficient magnetic dissipation.

Findings

Magnetic inclination angle likely around 45 degrees.

Dissipation timescale estimated at about 80 years.

High magnetization conflicts with observed low magnetic field.

Abstract

Magnetic dissipation is frequently invoked as a way of powering the observed emission of relativistic flows in Gamma Ray Bursts and Active Galactic Nuclei. Pulsar Wind Nebulae provide closer to home cosmic laboratories which can be used to test the hypothesis. To this end, we analyze the observational data on the spindown power of the Crab pulsar, energetics of the Crab nebula, and its magnetic field. We show that unless the magnetic inclination angle of the Crab pulsar is very close to 90 degrees the overall magnetization of the striped wind after total dissipation of its stripes is significantly higher than that deduced in the Kennel-Coroniti model and recent axisymmetric simulations of Pulsar Wind Nebulae. On the other hand, higher wind magnetization is in conflict with the observed low magnetic field of the Crab nebula, unless it is subject to efficient dissipation inside the nebula as well. For the likely inclination angle of 45 degrees the data require magnetic dissipation on the timescale about 80 years, which is short compared to the life-time of the nebula but long compared to the time scale of Crab's gamma-ray flares.