Harvard-Smithsonian Center for Astrophysics Patrick Slane Pulsar Wind Nebulae

Harvard-Smithsonian Center for Astrophysics Patrick Slane

Harvard-Smithsonian Center for Astrophysics Patrick Slane 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) The Pulsar Wind Zone

Harvard-Smithsonian Center for Astrophysics Patrick Slane 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 The Pulsar Wind Zone

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

Harvard-Smithsonian Center for Astrophysics Patrick Slane 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

Harvard-Smithsonian Center for Astrophysics Patrick Slane 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 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 pulsar axis van der Swaluw 2003 pulsar axis Elongated Structure of PWNe

Harvard-Smithsonian Center for Astrophysics Patrick Slane G Lu et al Elongated Structure of PWNe Crab Nebula pulsar spin G Roberts et al PSR B Gaensler et al C 58 Slane et al. 2004

Harvard-Smithsonian Center for Astrophysics Patrick Slane The Crab Nebula

Harvard-Smithsonian Center for Astrophysics Patrick Slane 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 Filamentary Structure in PWNe: Crab Nebula Jun 1996

Harvard-Smithsonian Center for Astrophysics Patrick Slane Crab Nebula - radio Crab Nebula – H  cont Filamentary Structure in PWNe: Crab Nebula 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? 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 N W

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

Harvard-Smithsonian Center for Astrophysics Patrick Slane 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 Nebula: L = 2.5 x 10 erg/s 37 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 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 jet ring v

Harvard-Smithsonian Center for Astrophysics Patrick Slane G : Home of a Young Pulsar Slane et al Matheson & Safi-Harb et al Camilo et al G 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

Harvard-Smithsonian Center for Astrophysics Patrick Slane Filamentary Structure in 3C 58 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 Slane et al. 2004

Harvard-Smithsonian Center for Astrophysics Patrick Slane 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 Spectral Structure of 3C 58

Harvard-Smithsonian Center for Astrophysics Patrick Slane van der Swaluw 2003 pulsar axis 3C 58: Structure of the Inner Nebula Central core is extended in 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 Suggests E-W axis for pulsar - consistent with E-W elongation of 3C 58 itself due to pinch effect in toroidal field Slane et al pulsar jet torus 12 arcsec For minimum energy field, the jet length gives a flow speed of

Harvard-Smithsonian Center for Astrophysics Patrick Slane PWN Jet/Torus Structure Komissarov & Lyubarsky 2003 pulsar 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 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 Patrick Slane Inner Structure in PWNe: Jets Crab Nebula (Weisskopf et al 2000) 40” = 0.4 pc PSR B (Gaensler et al 2002) 4’ = 6 pc Vela PWN (Pavlov et al 2003) Kommisarov & Lyubarsky (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?

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

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

Harvard-Smithsonian Center for Astrophysics Patrick Slane Reverse-Shock/PWN Interaction As PWN sweeps up material, reverse shock forms in ejecta - this propagates back to the SNR center and eventually interacts w/ PWN van der Swaluw, Downes, & Keegan 2003

Harvard-Smithsonian Center for Astrophysics Patrick Slane Reverse-Shock/PWN Interaction 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 van der Swaluw, Downes, & Keegan 2003

Harvard-Smithsonian Center for Astrophysics Patrick Slane Reverse-Shock/PWN Interaction 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 van der Swaluw, Downes, & Keegan 2003

Harvard-Smithsonian Center for Astrophysics Patrick Slane G : Sort of Shocking…

Harvard-Smithsonian Center for Astrophysics Patrick Slane G : 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

Harvard-Smithsonian Center for Astrophysics Patrick Slane A Disrupted PWN in G ? 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) Slane et al Whiteoak & Green 1996

Harvard-Smithsonian Center for Astrophysics Patrick Slane A Disrupted PWN in G ? 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? Slane et al. 2004

Harvard-Smithsonian Center for Astrophysics Patrick Slane “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 Bow Shocks: Theory ambient ISM unshocked pulsar wind shocked pulsar wind shocked ISM bow shock contact discontinuity termination shock Bucciantini (2002) } From B. Gaensler

Harvard-Smithsonian Center for Astrophysics Patrick Slane “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 Bow Shocks: Observation From B. Gaensler PSR J / “the Mouse” (Gaensler et al 2003) 30” X-rays Radio   } 2D hydro simulation (van der Swaluw & Gaensler 2004)