Pulsar Wind Nebulae Patrick Slane HarvardSmithsonian Center for

Pulsar Wind Nebulae Patrick Slane Harvard-Smithsonian Center for Astrophysics

http: //www. astroscu. unam. mx/neutrones/home. html Patrick Slane Harvard-Smithsonian Center for Astrophysics

The Pulsar Wind Zone • Rotating magnetosphere generates E X B wind - direct particle acceleration as well, yielding (e. g. Michel 1969; Cheng, Ho, & Ruderman 1986) • 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) Patrick Slane Harvard-Smithsonian Center for Astrophysics

The Pulsar Wind Zone • Rotating magnetosphere generates E X B wind - direct particle acceleration as well, yielding (e. g. Michel 1969; Cheng, Ho, & Ruderman 1986) • 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 Patrick Slane Harvard-Smithsonian Center for Astrophysics

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

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 Gaensler & Slane 2006 Patrick Slane • As SNR/PWN ages, reverse shock approaches/disrupts PWN - as pulsar reaches outer portions of SNR, a bow-shock nebula can form Harvard-Smithsonian Center for Astrophysics

Elongated Structure of PWNe pulsar axis Begelman & Li 1992 • 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 Patrick Slane van der Swaluw 2003 • 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 Harvard-Smithsonian Center for Astrophysics

Elongated Structure of PWNe 3 C 58 Slane et al. 2004 G 5. 4 -0. 1 PSR B 1509 -58 Lu et al. 2002 G 11. 2 -0. 3 pulsar spin Crab Nebula Roberts et al. 2003 Patrick Slane Gaensler et al. 2002 Harvard-Smithsonian Center for Astrophysics

The Crab Nebula Patrick Slane Harvard-Smithsonian Center for Astrophysics

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 Patrick Slane Harvard-Smithsonian Center for Astrophysics

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

The Crab Nebula in X-rays • Fine structure observed in Chandra image - poloidal loop structures surround torus as well (seen w/ HST too) Patrick Slane Harvard-Smithsonian Center for Astrophysics

The Crab Nebula in X-rays How does pulsar energize synchrotron nebula? Pulsar: P = 33 ms d. E/dt = 4. 5 x 10 38 erg/s Nebula: L x v = 2. 5 x 10 37 erg/s • X-ray jet-like structure appears to extend all the way to the neutron star jet - jet axis aligned with pulsar proper motion; same is true of Vela pulsar • inner ring of x-ray emission associated with shock wave produced by matter rushing away from neutron star ring - corresponds well with optical wisps delineating termination shock boundary Patrick Slane Harvard-Smithsonian Center for Astrophysics

G 21. 5 -0. 9: Home of a Young Pulsar • G 21. 5 -0. 9 is a composite SNR for which a radio pulsar with the 2 nd 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 22 -2 - column density is > 2 x 10 cm , distance ~5 kpc Matheson & Safi-Harb et al. 2005 Camilo et al. 2005 Slane et al. 2000 Patrick Slane Harvard-Smithsonian Center for Astrophysics

Filamentary Structure in 3 C 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 Patrick Slane Harvard-Smithsonian Center for Astrophysics

Spectral Structure of 3 C 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 Patrick Slane Harvard-Smithsonian Center for Astrophysics

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

pulsar PWN Jet/Torus Structure jet torus spin axis • 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 Komissarov & Lyubarsky 2003 Patrick Slane • 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 Harvard-Smithsonian Center for Astrophysics

Inner Structure in PWNe: Jets 40” = 0. 4 pc Crab Nebula (Weisskopf et al 2000) 4’ = 6 pc PSR B 1509 -58 (Gaensler et al 2002) Vela PWN (Pavlov et al 2003) • Relativistic flows: - motion, spectral analysis give v/c ~ 0. 3– 0. 6 • Collimated features - some curved at ends – why? • Wide range in brightness and size (0. 01– 6 pc) - how much energy input? • Primarily one-sided - Doppler boosting? • Perpendicular to inner ring - directed along spin axis? • Magnetic collimation / hoop stress? Patrick Slane Kommisarov & Lyubarsky (2003) Harvard-Smithsonian Center for Astrophysics

HESS Detection of PSR B 1509 -58 4’ = 6 pc 10 arcmin Patrick Slane Harvard-Smithsonian Center for Astrophysics

Reverse-Shock/PWN Interaction van der Swaluw, Downes, & Keegan 2003 • As PWN sweeps up material, reverse shock forms in ejecta Patrick Slane Harvard-Smithsonian Center for Astrophysics

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 Patrick Slane Harvard-Smithsonian Center for Astrophysics

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 Patrick Slane Harvard-Smithsonian Center for Astrophysics

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 Patrick Slane Harvard-Smithsonian Center for Astrophysics

G 292. 0+1. 8: Sort of Shocking… Patrick Slane Harvard-Smithsonian Center for Astrophysics

G 292. 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 Patrick Slane Harvard-Smithsonian Center for Astrophysics

A Disrupted PWN in G 327. 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) Patrick Slane Harvard-Smithsonian Center for Astrophysics

A Disrupted PWN in G 327. 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? Patrick Slane Harvard-Smithsonian Center for Astrophysics

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

Bow Shocks: Observation X-rays • “Stand-off distance” of shock set by ram pressure balance: Radio • Analytic solution for shape of bow shock: (Wilkin 1996) 30” PSR J 1747 -2958 / “the Mouse” (Gaensler et al 2003) • Forward (“bow”) and reverse (“termination”) shocks, separated by contact discontinuity } • Termination shock elongated by ratio of ~ 5: 1 Patrick Slane From B. Gaensler 2 D hydro simulation (van der Swaluw & Gaensler 2004) Harvard-Smithsonian Center for Astrophysics