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

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, June 28, 2011

PWNe • PWNe are hot bubbles (plerions) of 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) 28/06/2011 N. Bucciantini: HEPRO III 2011 2 Tuesday, June 28, 2011

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: 28/06/2011 N. Bucciantini: HEPRO III 2011 3 Tuesday, June 28, 2011

Sketch of PWN / SNR interaction Pulsar wind Relativistic bubble (PWN, plerion) • The SNR consists of a blast wave expanding in the ISM and by ejecta in free expansion • The ultrarelativistic magnetized TS pulsar wind inflate a plerion CD inside the SNR SNR shell SNR ejecta 28/06/2011 N. Bucciantini: HEPRO III 2011 4 Tuesday, June 28, 2011

Crab Nebula at various energies OPTICAL RADIO X-RAYS γ− rays (<100 MeV) ? 28/06/2011 N. Bucciantini: HEPRO III 2011 5 Tuesday, June 28, 2011

Polarization radio Vela, Dodson et al 03 G106.6+29, Kothes et al 06 Old nebulae interacting with ejecta - distorted stretched field in the back direction 28/06/2011 N. Bucciantini: HEPRO III 2011 6 Tuesday, June 28, 2011

Polarization radio Toroidal field Vela, Dodson et al 03 G106.6+29, Kothes et al 06 Old nebulae interacting with ejecta - distorted stretched field in the back direction 28/06/2011 N. Bucciantini: HEPRO III 2011 6 Tuesday, June 28, 2011

Fine structures Crab Vela • Crab nebula ( Weisskopf et al., 2000; Hester et al., 2002 ) • Vela pulsar ( Helfand et al., 2001; Pavlov et al., 2003 ) 28/06/2011 N. Bucciantini: HEPRO III 2011 7 Tuesday, June 28, 2011

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 ~ sin 2 ( θ ) 28/06/2011 N. Bucciantini: HEPRO III 2011 8 Tuesday, June 28, 2011

TS structure and flow pattern • The wind anisotropy shapes σ =0.03 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 28/06/2011 N. Bucciantini: HEPRO III 2011 9 Tuesday, June 28, 2011

Formation of polar jets by hoop stresses 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 σ =0.003 σ =0.01 σ =0.03 28/06/2011 N. Bucciantini: HEPRO III 2011 10 Tuesday, June 28, 2011

Modeling a striped wind case • Initial magnetic field with a narrow equatorial neutral sheet • Dissipation in a striped wind b=10 28/06/2011 N. Bucciantini: HEPRO III 2011 11 Tuesday, June 28, 2011

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 28/06/2011 N. Bucciantini: HEPRO III 2011 12 Tuesday, June 28, 2011

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 28/06/2011 N. Bucciantini: HEPRO III 2011 13 Tuesday, June 28, 2011

Comparison with Observations 28/06/2011 N. Bucciantini: HEPRO III 2011 14 Tuesday, June 28, 2011

Comparison with Observations 28/06/2011 N. Bucciantini: HEPRO III 2011 14 Tuesday, June 28, 2011

Photon Index Jet not correctly reproduced Mori 02 (required reacceleration) Higher index in the torus Brighter inner ring (recompression and boosting) 28/06/2011 N. Bucciantini: HEPRO III 2011 15 Tuesday, June 28, 2011

Time variability - wisps •Wisp moving outward •Year long limit cycle •Variability in the knot •Bubble in the jet v~ 0.6 c Variability in the knot structure Jet feature moving at 0.6 c Local instabilities or global modes? Slane 05, DeLaney 06 28/06/2011 N. Bucciantini: HEPRO III 2011 16 Tuesday, June 28, 2011

MHD variability - Flow 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 28/06/2011 N. Bucciantini: HEPRO III 2011 17 Tuesday, June 28, 2011

MHD variability - Flow 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 28/06/2011 N. Bucciantini: HEPRO III 2011 17 Tuesday, June 28, 2011

MHD variability - SASI The stable TS configuration Shear layer Shear layer 28/06/2011 N. Bucciantini: HEPRO III 2011 18 Tuesday, June 28, 2011

MHD variability - SASI 28/06/2011 N. Bucciantini: HEPRO III 2011 18 Tuesday, June 28, 2011

MHD variability - SASI The SASI TS instability A pressure wave is launched inside the nebula Eddy forms 28/06/2011 N. Bucciantini: HEPRO III 2011 18 Tuesday, June 28, 2011

MHD variability - SASI Pressure wave Pressure wave The SASI TS instability converge to axis moves outward A pressure wave is launched inside the nebula Eddy forms Eddy advected outward 28/06/2011 N. Bucciantini: HEPRO III 2011 18 Tuesday, June 28, 2011

MHD variability - SASI Pressure wave Pressure wave The SASI TS instability converge to axis moves outward A pressure wave is launched inside the nebula Eddy forms Eddy advected outward Compression waves in the jet Pressure wave reflected by the axis Pressure wave compresses the TS 28/06/2011 N. Bucciantini: HEPRO III 2011 18 Tuesday, June 28, 2011

MHD variability - Emission Outgoing wave pattern Large luminosity variations Features slow down as they move outward 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 28/06/2011 N. Bucciantini: HEPRO III 2011 19 Tuesday, June 28, 2011

MHD variability - Emission Outgoing wave pattern Large luminosity variations Features slow down as they move outward 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 28/06/2011 N. Bucciantini: HEPRO III 2011 19 Tuesday, June 28, 2011

MHD variability - High Energy Wilson-Hodge et al. 2010 ~ 2 yr Timescale 28/06/2011 N. Bucciantini: HEPRO III 2011 20 Tuesday, June 28, 2011

Flares Not from pulsar : Apr 2011 Flare! - flares are not pulsed or in phase - no variations in the Sep 2010 timing residual Feb 2009 Flare Flare Wilson-Hodge et al. 2011 28/06/2011 N. Bucciantini: HEPRO III 2011 21 Tuesday, June 28, 2011

Flares 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 28/06/2011 N. Bucciantini: HEPRO III 2011 22 Tuesday, June 28, 2011

Flares 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? 28/06/2011 N. Bucciantini: HEPRO III 2011 22 Tuesday, June 28, 2011

Free Expansion into Ejecta • Continuous energy injection - High synchrotron luminosity • PWN expands supersonically, R PWN ∝ t 6/5 • Pulsar at the center of PWN SNR G21.5-0.9 (X-rays) SNR G11.2-0.3 (X-rays) Matheson & Safi-Harb 2005 Kaspi et al. 2001 28/06/2011 N. Bucciantini: HEPRO III 2011 23 Tuesday, June 28, 2011

Reverberation 5/ 6 − 1/ 2 n 0 − 1/ 3 kyr • Reverse interacts with PWN after time t ~ 7 M 10 M sun E 51 • Compression; synchrotron burn-off at high energies • Effects of inhomogeneous ISM • Offset pulsar; filamentary structure; mixing forward shock PWN reverse shock van der Swaluw et al. (2004) 28/06/2011 N. Bucciantini: HEPRO III 2011 24 Tuesday, June 28, 2011