Model of Radio Emission from Spherically Symmetric Pulsar Wind Nebulae

1. ABSTRUCT We study spatially resolved radio emission from PWNe. We assume that a PWN has the pure toroidalB-field and the has power-law radial velocity profile. We apply the model to the Crab Nebula and succeed to reproduce the observed spatially integrated radio spectrum with a single power-law injection. The obtained radial velocity profile is very different from the model by Kennel & Coroniti and the spatially resolved radio emission in our model is inconsistent with that in observations. Further studies about the spherically symmetric PWNe are important to understand the origin of the radio emission from young PWNe. I IV Introduction Total spectrum of PWNe have large break Δα> 0.5 The spectrum is smooth at optical and we expect both components are same origin, i.e., injected from the central pulsar. • Model (1D PWN) • No diffusion & no syn. cooling because we consider evolution of radio emitting paricles. • Radial flow & toroidal B-field (+ induction eq.). • Injection from PSR (single PL, σ-parametar) • Introducing inner radius r0 and then main parameters are σ, αu, r0, γmin, γmax spectral index α (Fν∝να) The Crab Nebula Total Spectrum Model of Radio Emission from Spherically Symmetric Pulsar Wind Nebulae ST&Takahara 10 II • Pair Multiplicity of Pulsar Wind • (One-zone spectral model) • Broken Power-law injection. • Mean B-field ~ 100μG & • break energy γb ~ 106. • Radio emitting particles • require γmin ~ 102. • Number of particles inside Crab Nebula ~ 1051. • Corresponding pair multiplicity is κ ~ 4x106! • This contradicts theoretical studies of … • Pulsar magnetosphere (e.g., Daugherty & Harding(1982)) • Pulsar wind (e.g., Wilson&Rees(1978)) V • RESULTS • Integrated spectrum at radio is reproduced. • Projection of flux (consistent with uniform distribution) • Spectral index map (do not fit to observation) The Crab Nebula Total Spectrum lnN ∝γ-p1 ∝γ-p2 out in Shuta J. Tanaka Aoyama Gakuin University, Japan lnγ γmin γb γmax • Calculation(10MHz) • Observation(74MHz) Fν logFν Bietenholz+97 PSR r[pc] III • MOTIVATION • Beyond one-zone spectral model & comparing with spatially resolved observations. • Adiabatic cooling may be important because radio spectrum of some PWNe is reproduced by adiabatic cooling in one-zone model (ST&Takahara(2011)). • Calculation(10MHz) • α～+0.3 • Observation(74-1500MHz) • Centered on α= -0.299 Δα 1000 α Bietenholz+97 PSR r[pc] • CONCLUSIONS • Simple spherical model can create spectral break Δα > 0.5. • However, we need more studies to explain the whole characteristic of PWNe. • Spatially resolved observations are not reproduced. • Dynamics are very different from Kennel&Coroniti(1984)⇨ • FUTURE WORKS • Diffusion of radio emitting particle (beyond Kennel&Coroniti)? • Reconsideration of magnetosphere and pulsar wind studies? Pressure Distribution (Normalized @ r0) Our KC84 magnetic u∝r-0.16 u∝r-2⇒u∝r0 magnetic 2012, Aug. 20-25, IAU Symposium 291@Beijing, China particle particle 0.1pc Radius 2pc 0.1pc Radius 2pc