The relativistic wind in PWNe Niccolo Bucciantini Astronomy Group, - - PowerPoint PPT Presentation

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The relativistic wind in PWNe Niccolo Bucciantini Astronomy Group, NORDITA, Albanova University http://www.nordita.edu L. Del Zanna, E. Amato, D. Volpi, J.Arons, S. Komissarov, N. Camus 28/06/2011 N. Bucciantini: HEPRO III 2011 1 Tuesday,

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The relativistic wind in PWNe

Astronomy Group, NORDITA, Albanova University http://www.nordita.edu

  • L. Del Zanna, E. Amato, D. Volpi, J.Arons, S. Komissarov, N. Camus

Niccolo’ Bucciantini

Tuesday, June 28, 2011

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PWNe

  • PWNe are hot bubbles (plerions)
  • f relativistic particles and

magnetic field emitting non- thermal radiation (synchrotron - IC) from Radio to γ-ray.

  • Originated by the interaction of

the ultra-relativistic magnetized pulsar wind with the expanding SNR (or with the ISM)

  • Crab Nebula in optical: central

amorphous mass (continuum) + external filaments (lines)

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PWNe analytical MHD theory

  • Theoretical model for PWNe - 1-D steady-state (Rees

& Gunn 1974; Kennel & Coroniti, 1984) and self-similar

(Emmering & Chevalier, 1987) - free expansion phase. Basic assumptions:

  • The wind terminates with a strong MHD shock
  • Particles are accelerated at TS
  • Relativistic MHD flow in the PWN region
  • Synchrotron losses inside the nebula
  • Wind parameters derived by comparison with observations:

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Sketch of PWN / SNR interaction

  • The SNR consists of a blast

wave expanding in the ISM and by ejecta in free expansion

  • The ultrarelativistic magnetized

pulsar wind inflate a plerion inside the SNR Pulsar wind Relativistic bubble (PWN, plerion) SNR ejecta SNR shell TS CD

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Crab Nebula at various energies

RADIO X-RAYS OPTICAL γ−rays (<100 MeV)

?

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Polarization radio

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Vela, Dodson et al 03 G106.6+29, Kothes et al 06

Old nebulae interacting with ejecta - distorted stretched field in the back direction

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Polarization radio

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Vela, Dodson et al 03 G106.6+29, Kothes et al 06

Old nebulae interacting with ejecta - distorted stretched field in the back direction

Toroidal field

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Fine structures

  • Crab nebula (Weisskopf et al., 2000; Hester et al., 2002)
  • Vela pulsar (Helfand et al., 2001; Pavlov et al., 2003)

Crab Vela

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Wind models

Force-free (Contopulos et al 1999, Gruzinov 2005, Spitkovsky 2006) RMHD (Bogovalov 2001, Komissarov 2006, Bucciantini et al. 2006)

Lorentz factor ~ sin(θ) Energy flux ~ sin2(θ)

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TS structure and flow pattern

  • The wind anisotropy shapes

the TS structure. Downstream flow - equatorial collimation due to the TS shape:

  • A: ultrarelativistic pulsar wind
  • B: subsonic equatorial outflow
  • C: supersonic equatorial funnel
  • D: super-fastmagnetosonic flow
  • a: termination shock front
  • b: rim shock
  • c: fastmagnetosonic surface

σ=0.03

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Formation of polar jets by hoop stresses

σ=0.003 σ=0.03 σ=0.01

  • The global nebular flow changes with σ
  • Flow is diverted to the axis when equipartition is reached
  • For high magnetization (σ > 0.01) a supersonic jet is formed
  • Equipartition must be reached inside the PWN

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Modeling a striped wind case

  • Initial magnetic field with a narrow equatorial neutral sheet
  • Dissipation in a striped wind

b=10

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Comparison with Observations

Main torus Inner ring (wisps structure) Knot Back side of the inner ring

No jet - Axisymmetric assumption

Knot Ring Torus

Hester et al. 1995

Komissarov & Lyubarky 2004

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Striped wind and jet properties

What effect has the striped wind region size on the appearance of the jet? Where the wind magnetization is maximum? Equatorial region or polar? Wind with higher polar magnetization proposed by Arons 1998. σ=0.025, b=10 σ=0.1, b=1

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Comparison with Observations

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Comparison with Observations

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Photon Index

Brighter inner ring

Mori 02

Higher index in the torus

(recompression and boosting)

Jet not correctly reproduced

(required reacceleration)

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Time variability - wisps

  • Wisp moving outward
  • Year long limit cycle
  • Variability in the knot
  • Bubble in the jet v~ 0.6 c

Slane 05, DeLaney 06

Variability in the knot structure Jet feature moving at 0.6 c Local instabilities or global modes?

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MHD variability - Flow

17 Instability of the shear layers creates eddies at the rim shock Eddies are advected outward and a toroidal pressure wave is launched There is no wave reflection from the boundary Waves reflected on the axis modulate the TS shape The equatorial channel is kink unstable

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MHD variability - Flow

17 Instability of the shear layers creates eddies at the rim shock Eddies are advected outward and a toroidal pressure wave is launched There is no wave reflection from the boundary Waves reflected on the axis modulate the TS shape The equatorial channel is kink unstable

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MHD variability - SASI

18 The stable TS configuration

Shear layer Shear layer

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MHD variability - SASI

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MHD variability - SASI

18 The SASI TS instability

Eddy forms A pressure wave is launched inside the nebula

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MHD variability - SASI

18 The SASI TS instability

Eddy forms A pressure wave is launched inside the nebula Eddy advected

  • utward

Pressure wave converge to axis Pressure wave moves outward

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MHD variability - SASI

18 The SASI TS instability

Eddy forms A pressure wave is launched inside the nebula Eddy advected

  • utward

Pressure wave converge to axis Pressure wave moves outward Pressure wave reflected by the axis Compression waves in the jet Pressure wave compresses the TS

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MHD variability - Emission

19 Outgoing wave pattern Large luminosity variations Features slow down as they move

  • utward

Variability observed both in the knot and in the sprite Pressure waves produce variability in the axial emissivity Large striped wind are favored to produce a bright torus

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MHD variability - Emission

19 Outgoing wave pattern Large luminosity variations Features slow down as they move

  • utward

Variability observed both in the knot and in the sprite Pressure waves produce variability in the axial emissivity Large striped wind are favored to produce a bright torus

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MHD variability - High Energy

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Wilson-Hodge et al. 2010

~ 2 yr Timescale

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Flares

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Not from pulsar :

  • flares are not pulsed or

in phase

  • no variations in the

timing residual

Sep 2010 Flare Apr 2011 Flare! Feb 2009 Flare

Wilson-Hodge et al. 2011

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Flares

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Unlikely MHD origin like the slow variability of the wisps:

  • MHD effects are

achromatic

  • size of the accelerator is

very small (day-light)

  • unlikely high magnetic

field

Wilson-Hodge et al. 2011

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Flares

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Unlikely MHD origin like the slow variability of the wisps:

  • MHD effects are

achromatic

  • size of the accelerator is

very small (day-light)

  • unlikely high magnetic

field

Wilson-Hodge et al. 2011

Electrostatic acceleration?

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Free Expansion into Ejecta

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  • Continuous energy injection - High synchrotron luminosity
  • PWN expands supersonically, RPWN ∝ t 6/5
  • Pulsar at the center of PWN

SNR G21.5-0.9 (X-rays) Matheson & Safi-Harb 2005 SNR G11.2-0.3 (X-rays) Kaspi et al. 2001

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Reverberation

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  • Reverse interacts with PWN after time
  • Compression; synchrotron burn-off at high energies
  • Effects of inhomogeneous ISM
  • Offset pulsar; filamentary structure; mixing

t ~ 7M10M sun

5/ 6

E51

−1/ 2n0 −1/ 3 kyr

van der Swaluw et al. (2004)

forward shock PWN reverse shock

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Reverberation

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  • Reverse interacts with PWN after time
  • Compression; synchrotron burn-off at high energies
  • Effects of inhomogeneous ISM
  • Offset pulsar; filamentary structure; mixing

t ~ 7M10M sun

5/ 6

E51

−1/ 2n0 −1/ 3 kyr

Vela (radio) Duncan et al. 1996 van der Swaluw et al. (2004)

forward shock PWN reverse shock

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Transition to bow shock

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  • PWN expands into shocked ejecta
  • “Relic” radio PWN left behind
  • New PWN around pulsar (X-ray)

van der Swaluw (2004)

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Transition to bow shock

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  • PWN expands into shocked ejecta
  • “Relic” radio PWN left behind
  • New PWN around pulsar (X-ray)

SNR G327.1-1.1, Gaensler & van der Swaluw (2004)

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Transition to bow shock

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  • PWN expands into shocked ejecta
  • “Relic” radio PWN left behind
  • New PWN around pulsar (X-ray)

SNR G327.1-1.1, Gaensler & van der Swaluw (2004) SNR W44 (Frail et al. 1996, Giacani et al. 1997)

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Bow Shock PWN

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  • Most pulsars kick velocity is supersonic in ISM
  • Forward shock visible in Hα
  • PWN visible as a radio and X-rays tail

Hα X- rays

15”

PSR B1957+20 (Stappers et al. 2003) PSR B2224+65 (Chatterjee & Cordes 2002)

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Are we over-biased by Crab ?

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Not every PWN is Crab Not all Crab properties are universal

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Are we over-biased by Crab ?

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Not every PWN is Crab Not all Crab properties are universal

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Are we over-biased by Crab ?

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Not every PWN is Crab Not all Crab properties are universal

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Summary and conclusions

  • PWNe are well defined system, where a base agreement on engine and

emission properties has beed reached

  • There is now a “canonical” model which can explain many of the
  • bserved features
  • There are still open areas of research for old objects
  • Tools for PWNe study are easy to use, and widely available now
  • Still hard to derive fully consistent models that can account for all of the
  • bserved properties
  • Holes remain in the entire picture that NEED to be filled
  • Not all PWNe are Crab “clones” - Nor should every model!

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Summary and conclusions

  • PWNe are well defined system, where a base agreement on engine and

emission properties has beed reached

  • There is now a “canonical” model which can explain many of the
  • bserved features
  • There are still open areas of research for old objects
  • Tools for PWNe study are easy to use, and widely available now
  • Still hard to derive fully consistent models that can account for all of the
  • bserved properties
  • Holes remain in the entire picture that NEED to be filled
  • Not all PWNe are Crab “clones” - Nor should every model!

Thank you

Tuesday, June 28, 2011