Structure and Evolution

Structure and Evolution

of Pulsar Wind NebulaePatrick Slane MODE SNR/PWN Workshop Orsay, France (6/19/2013)

Take In:

Orsay, France (6/19/2013)Patrick Slane MODE SNR/PWN Workshop

• Pulsars are born as reservoirs of tremendous rotational energy

• Their strong magnetic fields and rapid rotation rates promote loss of rotational energy through formation of a relativistic magnetized wind

• Particles from that wind eventually merge into the ISM. Pulsars thus convert rotational energy into diffuse relativistic particle energy in the ISM

How can we possibly follow the conversion of a rotational energyexceeding 1031 erg cm-3 to its ultimate fate as a particle energydensity comprising a tiny fraction of 1 eV cm-3? (Hint: It isn’t easy,and still far from perfect…)

Jet/Torus Structure in PWNe

Patrick Slane MODE SNR/PWN Workshop Orsay, France (6/19/2013)

van den Heuvel 2006

• Anisotropic flux with maximum energy flux in equatorial zone - radial particle outflow - striped wind from Poynting flux decreases away from equator

- Wind in nebula is particle-dominated

€

F ≈Ω2ψ 0

2

4πc 2R2sin2 θ +

1

σ 0

⎛

⎝ ⎜

⎞

⎠ ⎟

Lyubarsky 2002





€

F ≈Ω2ψ 0

2

4πc 2R2sin2 θ +

1

σ 0

⎛

⎝ ⎜

⎞

⎠ ⎟



- Doppler beaming indicates torus flows with v > 0.4c (e.g., Lu et al. 2001)

€

F ≈Ω2ψ 0

2

4πc 2R2sin2 θ +

1

σ 0

⎛

⎝ ⎜

⎞

⎠ ⎟

• Polar jets form - subject to kink instabilities - outflow speeds > 0.2c (e.g. Gaensler et al. 2002)



Crab

G54.1+0.3

Vela

Seward et al. 2006

Lu et al. 2001

Pavlov et al. 2003

• Magnetic tension in equatorial plane results in elongation along rotation axis



Begelman & Li 1992

puls

ar a

xis


Crab

G54.1+0.3

3C 58

Seward et al. 2006

Lu et al. 2001

Slane et al. 2004




€

F ≈Ω2ψ 0

2

4πc 2R2sin2 θ +

1

σ 0

⎛

⎝ ⎜

⎞

⎠ ⎟

• Magnetic tension in equatorial plane results in elongation along rotation axis



Begelman & Li 1992

puls

ar a

xis


Crab

G54.1+0.3

3C 58

Hester et al. 2008

Lu et al. 2001

Slane et al. 2004




€

F ≈Ω2ψ 0

2

4πc 2R2sin2 θ +

1

σ 0

⎛

⎝ ⎜

⎞

⎠ ⎟

ISM

Sh

ock

ed ISM

Sh

ock

ed E

ject

a

Unsh

ock

ed

Eje

cta

PW

N

Puls

ar

Win

dForward Shock

Reverse ShockPWN Shock

PulsarTerminationShock

• Pulsar - injects particles and Poynting flux

• Pulsar Wind - sweeps up ejecta; shock decelerates flow, accelerates particles; PWN forms

• Supernova Remnant - sweeps up ISM; reverse shock heats ejecta; ultimately compresses PWN; energy distribution of particles in nebula tracks evolution; instabilities at PWN/ejecta interface may allow particle escape

Gaensler & Slane 2006


PWNe and Their SNRs

Example: G292.0+1.8

Chandra/ACIS

Park et al. 2007

4.0-7.0 keVRed: O Ly, Ne He

Orange: Ne Ly

Green: Mg He

Blue: Si He, S He


Example: G292.0+1.8

Chandra/ACIS

Red: O Ly, Ne He

Orange: Ne Ly

Green: Mg He

Blue: Si He, S He


Lee et al. 2010

Park et al. 2007

• X-rays reveal shocked wind from massive progenitor star

PWN Evolution

€

˙ E = IΩ ˙ Ω = ˙ E 0 1+t

τ

⎡ ⎣ ⎢

⎤ ⎦ ⎥

−n +1

n−1

energy input and swept-up ejecta mass

€

dM

dt= 4πR2ρ SN (v − R / t)

€

d4πR3

3pi

⎡

⎣ ⎢

⎤

⎦ ⎥

dt= ˙ E − pi 4πR2 dR

dt

€

Mdvdt

= 4πR2 pi − ρ SN v− R / t( )2

[ ]

PWN evolution

see Gelfand et al. 2009


PWN Evolution

€

˙ E = IΩ ˙ Ω = ˙ E 0 1+t

τ

⎡ ⎣ ⎢

⎤ ⎦ ⎥

−n +1

n−1

energy input and swept-up ejecta mass

€

dM

dt= 4πR2ρ SN (v − R / t)

€

d4πR3

3pi

⎡

⎣ ⎢

⎤

⎦ ⎥

dt= ˙ E − pi 4πR2 dR

dt

€

Mdvdt

= 4πR2 pi − ρ SN v− R / t( )2

[ ]

PWN evolution


Vorster et al. 2013

Evolution of PWN Emission

• Spin-down power is injected into the PWN at a time-dependent rate

• Assume input spectrum (e.g., PL):

- note that studies of Crab and other PWNe suggest that there may be multiple components€

Q(t) = Q0 (t)(Ee / Eb )−α€

˙ E = IΩ ˙ Ω = ˙ E 0 1+tτ

⎛ ⎝ ⎜

⎞ ⎠ ⎟−

n+1

n−1

• Get associated synchrotron and IC emission from electron population in the evolved nebula - combined information on observed spectrum and system size provide constraints on underlying structure and evolution


Evolution of PWN Emission

• Spin-down power is injected into the PWN at a time-dependent rate

• Assume input spectrum (e.g., PL):

- note that studies of Crab and other PWNe suggest that there may be multiple components€

Q(t) = Q0 (t)(Ee / Eb )−α€

˙ E = IΩ ˙ Ω = ˙ E 0 1+tτ

⎛ ⎝ ⎜

⎞ ⎠ ⎟−

n+1

n−1

• Get associated synchrotron and IC emission from electron population in the evolved nebula - combined information on observed spectrum and system size provide constraints on underlying structure and evolution

1000 yr2000 yr5000 yr

CMBinverse

Comptonsynchrotron


Injection from Relativistic Shocks

Spitkovsky 2008

• PIC simulations of particle acceleration in relativistic shocks show build-up of energetic particles (Spitkovsky 2008)

• Multi-component input spectrum: Maxwellian + power law – and possibly more complex if conditions differ at different acceleration sites


PWN Structure & Evolution: 3C 58

Slane et al. 2004


Slane et al. 2008

• Thermal X-rays evident from shocked ejecta (Bocchino et al. 2001; Slane et al. 2004)

• Spectrum of torus indicates complex injection spectrum (Slane et al. 2008)

- evidence of position-dependent acceleration?

PWN Structure & Evolution: SNR 0540-69CXO

Kaaret et al. 2001

Mignani et al. 2012


• Multi- studies reveal 0-rich ejecta, bright PWN, young pulsar, expanding SNR shell

• Broadband spectrum shows evolutionary break - disconnect in X-rays complicates interpretation; may indicate complex injection spectrum

G21.5-0.9Matheson & Safi-Harb 2005

CXO


36 arcsec

• X-rays reveal SNR shell and PWN with compact core and (Slane et al. 2000)

- shell from dust scattering, DSA, and ejecta (Bocchino et al. 2005)

- radio observations identify young, faint pulsar (Camilo et al. 2006)

G21.5-0.9Matheson & Safi-Harb 2005

CXO

Spitzer 24/8 m





• PWN and torus detected in IR - Broadband spectrum of torus shows evidence of structure between IR and X-ray

G21.5-0.9

Zajczyk et al. 2012

Ks linear-polarized intensity

[Fe II] 1.64 m





• PWN and torus detected in IR - Broadband spectrum of torus shows evidence of structure between IR and X-ray

• [Fe II] 1.64 mm image shows shocked ejecta surrounding PWN

• Polarization in IR indicates magnetic field with toroidal geometry

RS Interactions: G327.1-1.1

• G327.1-1.1 is a composite SNR for which radio morphology suggests PWN/RS interaction

Patrick Slane MODE SNR/PWN Workshop Orsay, France (6/19/2013)Temim et al. 2009

t = 20,000 yr

Blondin et al. 2001

high

low



prongs

cometarystructure

tail

pulsar + torus?



Radio Simulation

prongs

cometarystructure

tail

pulsar + torus?

RS Interactions: MSH 15-56

• Radio observations reveal shell with bright, flat-spectrum nebula in center - no pulsar known, but surely a PWN - nebula significantly displaced from SNR center


• X-ray studies show thermal shell w/ very faint hard emission near PWN - pulsar candidate seen as hard point source w/ faint X-ray trail extending to PWN

Temim et al. 2013


• Radio observations reveal shell with bright, flat-spectrum nebula in center - no pulsar known, but surely a PWN - nebula significantly displaced from SNR center


Temim et al. 2013



• X-ray spectrum gives n0 ≈ 0.1 cm-3

• SNR/PWN modeling gives t ≈ 12 kyr - SNR reverse shock has completely disrupted PWN

• Fermi observations of MSH 15-56 may be consistent with emission from an evolved PWN - if correct, pulsar has essentially departed relic PWN and is injecting particles into newly-forming nebula - additional observations required to better constrain ambient density and ejecta mass

Temim et al. 2013


de Jager et al. 2008

LaMassa et al. 2008

pulsarwind

ejecta

cocoon

RadioPWN

pulsar

Vela X: An Evolved PWN


H.E.S.S.contours

Fermi LATcontours


Hinton et al. 2011

• TeV emission observed concentrated along cocoon - GeV emission observed throughout PWN, but brightest region is offset from TeV peak

• TeV peak may be recent injection into cocoon following RS interaction - older energetic particles may have been lost to diffusion; however…


H.E.S.S.contours

Fermi LATcontours

hard emissionat Fermi LAT

peak

nonthermal emission hardalong cocoon, but soft

in eastern PWN as expectedfrom synchrotron losses


Re-acceleration

of low energy electrons, producing

GeV IC peak and flat X-ray

spectrum?

Take Away

• The magnetic/particle pulsar wind is axisymmetric and particle-dominated. It creates a nebula that drives itself through the interior of its host SNR. - The particle spectrum is complicated. This affects the multi- spectrum.

• The evolution of the wind nebula is strongly affected by that of its surrounding SNR, particularly the mass of its ejecta, and the density of its surroundings. - Early evolution can be dominated by massive radiative losses. Late evolution can be dominated by asymmetric crushing of nebula. This may increase diffusive escape of particles.

• Our models for PWN evolution can be directly tied to phenomena that we can image, and spectral evolution that we can resolve. The picture is still evolving, but we are clearly on the right track.


• Pulsars are born as reservoirs of tremendous rotational energy

• Their strong magnetic fields and rapid rotation rates promote loss of rotational energy through formation of a relativistic magnetized wind

• Particles from that wind eventually merge into the ISM. Pulsars thus convert rotational energy into diffuse relativistic particle energy in the ISM

Summary• Multiwavelength studies of PWNe reveal: - spin properties of central engines - geometry of systems - spatially-resolved spectra - interaction with supernova ejecta - presence of freshly-formed dust

• These lead to constraints on: - particle acceleration in relativistic shocks - formation of jets - physics of pulsar magnetospheres - nature of progenitor stars - early and late-phase evolution of pulsar winds

• Current advances are being made across the electromagnetic spectrum, as well as in theoretical modeling, and point the way for investigations in virtually every wavelength band.


Structure and Evolution

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