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Pulsar Wind Nebulae

Pulsar Wind Nebulae. http://www.astroscu.unam.mx/neutrones/home.html. Rotating magnetosphere generates E X B wind - direct particle acceleration as well, yielding (e.g. Michel 1969; Cheng, Ho, & Ruderman 1986). The Pulsar Wind Zone. Magnetic polarity in

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Pulsar Wind Nebulae

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  1. Pulsar Wind Nebulae

  2. http://www.astroscu.unam.mx/neutrones/home.html

  3. Rotating magnetosphere • generates E X B wind • - direct particle acceleration • as well, yielding • (e.g. Michel 1969; Cheng, • Ho, & Ruderman 1986) The Pulsar Wind Zone • Magnetic polarity in • wind alternates spatially • - magnetically “striped” wind • - does reconnection result in • conversion to kinetic energy? • (e.g. Coroniti 1990, Michel • 1994, Lyubarsky 2003)

  4. Rotating magnetosphere • generates E X B wind • - direct particle acceleration • as well, yielding • (e.g. Michel 1969; Cheng, • Ho, & Ruderman 1986) The Pulsar Wind Zone • Magnetic polarity in • wind alternates spatially • - magnetically “striped” wind • - does reconnection result in • conversion to kinetic energy? • (e.g. Coroniti 1990, Michel • 1994, Lyubarsky 2003) • Wind expands until ram • pressure is balanced by • surrounding nebula • - flow in outer nebula restricts • inner wind flow, forming • pulsar wind termination • shock

  5. b } + Pulsar G + logarithmic radial scale + + + Wind R MHD Shock Blast Wave Particle Flow Ha or ejecta shell - spectral break at where synchrotron lifetime of particles equals SNR age - radial spectral variation from burn-off of high energy particles Pulsar Wind Nebulae • Expansion boundary condition at • forces wind termination shock at • - wind goes from inside to • at outer boundary • Pulsar wind is confined by pressure • in nebula • - wind termination shock obtain by integrating radio spectrum • Wind is described by magnetization • parameter • s = ratio of Poynting flux to particle • flux in wind • Pulsar accelerates • particle wind • wind inflates bubble • of particles and • magnetic flux • particle flow in B-field • creates synchrotron • nebula

  6. Pulsar Wind Nebulae • Young NS powers a particle/magnetic • wind that expands into SNR ejecta • - toroidal magnetic field results in • axisymmetric equatorial wind • Termination shock forms where pulsar • wind meets slowly expanding nebula • - radius determined by balance of • ram pressure and pressure in nebula • As PWN accelerates higher density • ejecta, R-T instabilities form • - optical/radio filaments result • As SNR/PWN ages, reverse shock • approaches/disrupts PWN • - as pulsar reaches outer portions of SNR, • a bow-shock nebula can form Gaensler & Slane 2006

  7. pulsar axis van der Swaluw 2003 Begelman & Li 1992 Elongated Structure of PWNe pulsar axis • Dynamical effects of toroidal field • result in elongation of nebula along • pulsar spin axis • - profile similar for expansion into ISM, • progenitor wind, or ejecta profiles • - details of structure and radio vs. X-ray • depend on injection geometry and B • MHD simulations give differences in • detail, but similar results overall • - B field shows variations in interior • - turbulent flow and cooling could result in • additional structure in emission

  8. 3C 58 Slane et al. 2004 G5.4-0.1 PSR B1509-58 Lu et al. 2002 G11.2-0.3 pulsar spin Roberts et al. 2003 Gaensler et al. 2002 Elongated Structure of PWNe Crab Nebula

  9. The Crab Nebula

  10. Filamentary Structure in PWNe: Crab Nebula • Optical filaments show dense ejecta • - total mass in filaments is small; still • expanding into cold ejecta? • Rayleigh-Taylor fingers produced as • relativistic fluid flows past filaments • - continuum emission appears to reside • interior to filaments; filamentary shell Jun 1996

  11. Crab Nebula - radio N Filamentary Structure in PWNe: Crab Nebula • Optical filaments show dense ejecta • - total mass in filaments is small; still • expanding into cold ejecta? • Rayleigh-Taylor fingers produced as • relativistic fluid flows past filaments • - continuum emission appears to reside • interior to filaments; filamentary shell W • Radio emission shows structure • similar to optical line emission • - interaction with relativistic fluid in PWN • forms nonthermal filaments? • Overall morphology is elliptical • - suggestive of pulsar rotation axis with • southeast-northwest orientation • What do we see in in X-rays? Crab Nebula – Ha + cont

  12. The Crab Nebula in X-rays • Fine structure observed in Chandra • image • - poloidal loop structures surround torus • as well (seen w/ HST too)

  13. v ring The Crab Nebula in X-rays How does pulsar energize synchrotron nebula? Pulsar: P = 33 ms dE/dt = 4.5 x 10 erg/s 38 37 Nebula:L = 2.5 x 10 erg/s x • X-ray jet-like structure appears • to extend all the way to the • neutron star • - jet axis aligned with pulsar proper • motion; same is true of Vela pulsar jet • inner ring of x-ray emission • associated with shock wave • produced by matter rushing • away from neutron star - corresponds well with optical wisps delineating termination shock boundary

  14. Camilo et al. 2005 Slane et al. 2000 G21.5-0.9: Home of a Young Pulsar • G21.5-0.9 is a composite SNR for which a radio • pulsar with the 2nd highest spin-down power has • recently been discovered (Camilo et al. 2005) • - • -  ~ 4.8 kyr; true age more likely < 1 kyr • Merged 351 ks HRC observation reveals point • source embedded in compact nebula (torus?) • - no X-ray pulsations observed • - column density is > 2 x 10 cm , distance ~5 kpc 22 -2 Matheson & Safi-Harb et al. 2005

  15. Filamentary Structure in 3C 58 Slane et al. 2004 • X-ray emission shows considerable filamentary structure • - particularly evident in higher energy X-rays • Radio structure is remarkably similar, both for filaments and overall size

  16. Spectral Structure of 3C 58 • Radial steepening of spectral index shows aging • of synchrotron-emitting electrons • - consistent with injection from central pulsar • Modeling of spectral index in expected toroidal • field is unable to reproduce the observed profiles • - model profile has much more rapid softening of spectrum • (Reynolds 2003) • - diffusive particle transport and mixing may be occurring

  17. pulsar axis pulsar van der Swaluw 2003 jet torus 3C 58: Structure of the Inner Nebula 12 arcsec Slane et al. 2002 • Suggests E-W axis for pulsar • - consistent with E-W elongation of 3C 58 • itself due to pinch effect in toroidal field • Central core isextendedin N/S direction • - suggestive of inner Crab region with structure • from wind termination shock zone • 65 ms pulsar at center: • Pressure in radio nebula: • X-ray spectrum of jet shows no break • from synchrotron cooling • For minimum energy field, the jet • length gives a flow speed of

  18. pulsar jet torus PWN Jet/Torus Structure • Poynting flux from outside pulsar light • cylinder is concentrated in equatorial • region due to wound-up B-field • - termination shock radius decreases with • increasing angle from equator • For sufficiently high magnetization • parameter ( ~ 0.01), magnetic stresses • can divert particle flow back inward • - collimation into jets may occur • - asymmetric brightness profile from Doppler • beaming • Collimation is subject to kink instabilities • - magnetic loops can be torn off near TS and • expand into PWN (Begelman 1998) • - many pulsar jets are kinked or unstable, • supporting this picture spin axis Komissarov & Lyubarsky 2003

  19. 4’ = 6 pc 40” = 0.4 pc Crab Nebula (Weisskopf et al 2000) PSR B1509-58 (Gaensler et al 2002) Inner Structure in PWNe: Jets Vela PWN (Pavlov et al 2003) • Collimated features • - some curved at ends – why? • Wide range in brightness and • size (0.01–6 pc) • - how much energy input? • Perpendicular to inner ring • - directed along spin axis? • Relativistic flows: • - motion, spectral analysis • give v/c ~ 0.3–0.6 • Primarily one-sided • - Doppler boosting? • Magnetic collimation / hoop • stress? Kommisarov & Lyubarsky (2003)

  20. 4’ = 6 pc HESS Detection of PSR B1509-58 10 arcmin

  21. Reverse-Shock/PWN Interaction van der Swaluw, Downes, & Keegan 2003 • As PWN sweeps up material, reverse shock forms in ejecta

  22. Reverse-Shock/PWN Interaction van der Swaluw, Downes, & Keegan 2003 • As PWN sweeps up material, reverse shock forms in ejecta • - this propagates back to the SNR center and eventually interacts w/ PWN

  23. Reverse-Shock/PWN Interaction van der Swaluw, Downes, & Keegan 2003 • As PWN sweeps up material, reverse shock forms in ejecta • - this propagates back to the SNR center and eventually interacts w/ PWN • PWN can be disrupted, then re-form

  24. Reverse-Shock/PWN Interaction van der Swaluw, Downes, & Keegan 2003 • As PWN sweeps up material, reverse shock forms in ejecta • - this propagates back to the SNR center and eventually interacts w/ PWN • PWN can be disrupted, then re-form • - eventually bow-shock can form from supersonic pulsar motion

  25. G292.0+1.8: Sort of Shocking…

  26. G292.0+1.8: Sort of Shocking… • Oxygen and Neon abundances seen in ejecta • are enhanced above levels expected; very • little iron observed (Park et al. 2003) • - reverse shock appears to still be progressing • toward center; not all material synthesized in • center of star has been shocked • - pressure in PWN is higher than in ejecta as • well  reverse shock hasn’t reached PWN • Pulsar is offset from geometric center of SNR • - age and offset can give velocity estimate • Emission from around pulsar is also elongated • - if interpreted as jet, this could imply kick velocity • is (somewhat) aligned with rotation axis

  27. A Disrupted PWN in G327.1-1.1? Slane et al. 1999 Whiteoak & Green 1996 • Radio image shows shell with bright PWN in center • - distinct “radio finger” observed in PWN • Extended X-ray emission observed in central region • - ROSAT image shows X-ray emission trails away from central plerion • - faint compact X-ray source located at tip of radio finger (Slane et al. 1999)

  28. A Disrupted PWN in G327.1-1.1? Slane et al. 2004 • Radio image shows shell with bright PWN in center • - distinct “radio finger” observed in PWN • Extended X-ray emission observed in central region • - ROSAT image shows X-ray emission trails away from central plerion • - faint compact X-ray source located at tip of radio finger (Slane et al. 1999) • Chandra observation shows compact source w/ trail of emission • - has PWN been disrupted by reverse shock?

  29. Bow Shocks: Theory • “Stand-off distance” of shock • set by ram pressure balance: • Analytic solution for shape • of bow shock: (Wilkin 1996) • Forward (“bow”) and reverse • (“termination”) shocks, separated • by contact discontinuity • Termination shock elongated • by ratio of ~ 5:1 termination shock bow shock contact discontinuity ambient ISM shocked ISM shocked pulsar wind unshocked pulsar wind } Bucciantini (2002) From B. Gaensler

  30. Bow Shocks: Observation X-rays Radio • “Stand-off distance” of shock • set by ram pressure balance: • Analytic solution for shape • of bow shock: (Wilkin 1996) • Forward (“bow”) and reverse • (“termination”) shocks, separated • by contact discontinuity • Termination shock elongated • by ratio of ~ 5:1  30” PSR J1747-2958 / “the Mouse” (Gaensler et al 2003)  } From B. Gaensler 2D hydro simulation (van der Swaluw & Gaensler 2004)

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