The Crab Nebula and its Pulsar

Abstract

The Crab looks (presently) atypically slow because we only see its bright interior. The latter consists of (i) a thermal component, of temperature T ≳ 10⁴ K, density n = 10^{3.5 ± 0.5} cm^-3, mass ≳ 1M_⊙, and volume-filling factor f ≈ 10^-3, composed of ≳ 10⁴ filaments. The volume is filled by (ii) relativistic pair plasma, of energy distribution N_γ d_γ ∼ γ^-2.2 d_γ between γ = 10^5.5 and 10^8.8, which is continually injected by the pulsar; it is essentially weightless. Moreover, (iii) there is a bath of multiply reflected 30 Hz waves, strong enough to have post-accelerated the thermal filaments by 8%.

If the Crab’s progenitor was a blue giant with a fast, low-density wind, most of the ejected matter finds itself presently in the low-density CSM where it is too thin to be (easily) detected, both in emission and absorption.