Heidelberg 2008 Patrick Slane (CfA) Pulsar Wind Nebulae

Heidelberg 2008 Patrick Slane (CfA) Pulsar Wind Nebulae Expansion boundary condition at forces wind termination shock at - wind goes from v = c/3 1/2 inside R w to v ~ R N /t 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 R  F Slane et al. 2004

Heidelberg 2008 Patrick Slane (CfA) Broadband Emission from PWNe Spin-down power is injected into the PWN at a time-dependent rate Based on studies of Crab Nebula, there appear to be two populations – relic radio-emitting electrons and electrons injected in wind (Atoyan & Aharonian 1996) Get associated synchrotron and IC emission from electron population, and some assumed B field (e.g. Venter & dE Jager 2006) Zhang et al. 2008

Heidelberg 2008 Patrick Slane (CfA) Broadband Emission from PWNe Del Zanna et al Volpi et al More completely, assume wind injected at termination shock, with radial particle distribution and latitude-dependent magnetic component: Evolve nebula considering radiative and adiabatic losses to obtain time- and spatially-dependent electron spectrum and B field (e.g. Volpi et al. 2008) - integrate over synchrotron and IC emissivity to get spectrum See also talk by O.C. de Jager

Heidelberg 2008 Patrick Slane (CfA) Connecting the Synchrotron and IC Emission Energetic electrons in PWNe produce both synchrotron and inverse-Compton emission - for electrons with energy E TeV, synchrotron inverse-Compton - comparing photon energies from given electron population gives B (e.g. Atoyan & Aharonian 1999) Similarly, relative fluxes f E = E 2 f(E) = S give B : For low B, synchrotron lifetime is long, and f ic /f s is large - can expect bright TeV emission from collection of long-lived electrons; could explain (some of the?) “dark” sources

Heidelberg 2008 Patrick Slane (CfA) A Point About Injection: 3C 58 Slane et al C 58 is a bright, young PWN - morphology similar to radio/x-ray; suggests low magnetic field - low-frequency spectral break suggests possible injection break PWN and torus region observed in Spitzer/IRAC and CFHT observations - jet structure not seen above diffuse emission

Heidelberg 2008 Patrick Slane (CfA) A Point About Injection: 3C 58 3C 58 is a bright, young PWN - morphology similar to radio/x-ray; suggests low magnetic field - low-frequency spectral break suggests possible injection break PWN and torus region observed in Spitzer/IRAC and CFHT observations - jet structure not seen above diffuse emission E Flux Density Injection Nebula Synchrotron Break

Heidelberg 2008 Patrick Slane (CfA) Spitzer Observations of 3C 58 VLA IRAC 3.6  m Chandra Bietenholz 2006 IRAC 4.5  m Slane et al. 2004Slane et al C 58 is a bright, young PWN - morphology similar to radio/x-ray; suggests low magnetic field - low-frequency spectral break suggests possible injection break PWN and torus region observed in Spitzer/IRAC and CFHT observations - jet structure not seen above diffuse emission

Heidelberg 2008 Patrick Slane (CfA) Spitzer Observations of 3C 58 3C 58 is a bright, young PWN - morphology similar to radio/x-ray; suggests low magnetic field - low-frequency spectral break suggests possible injection break PWN and torus region observed in Spitzer/IRAC and CFHT observations - jet structure not seen above diffuse emission IR flux for entire nebula falls within extrapolation of x-ray spectrum - indicates single break just below IR - sub-mm observations would be of interest Torus spectrum requires change in slope between IR and x-ray bands - challenges assumptions of single power law for injection into nebula; TeV observations should provide constraints Slane et al. 2008

Heidelberg 2008 Patrick Slane (CfA) Spitzer Observations of 3C 58 PRELIMINARY 3C 58 is a bright, young PWN - morphology similar to radio/x-ray; suggests low magnetic field - low-frequency spectral break suggests possible injection break PWN and torus region observed in Spitzer/IRAC and CFHT observations - jet structure not seen above diffuse emission IR flux for entire nebula falls within extrapolation of x-ray spectrum - indicates single break just below IR - sub-mm observations would be of interest Torus spectrum requires change in slope between IR and x-ray bands - challenges assumptions of single power law for injection into nebula; TeV observations should provide constraints

Heidelberg 2008 Patrick Slane (CfA) MSH Contains PWN powered by energetic pulsar B ( Edot = erg s -1 ) - complex nebula, with arcs, time-varying clumps, and bright jet extending to SE HESS observations reveal emission with extended morphology following jet - similar morphology to x-ray synchrotron emission suggests leptonic origin - IC model requires B~17  G and an anomalously high energy density in dust IR emission, possibly from SNR (Aharonian et al. 2005) - Zhang et al. (2008) find similar results from broad-band evolutionary model (slightly higher B, lower U dust )

Heidelberg 2008 Patrick Slane (CfA) 6 arcmin MSH Aharonian et al Contains PWN powered by energetic pulsar B ( Edot = erg s -1 ) - complex nebula, with arcs, time-varying clumps, and bright jet extending to SE HESS observations reveal emission with extended morphology following jet - similar morphology to x-ray synchrotron emission suggests leptonic origin - IC model requires B~17  G and an anomalously high energy density in dust IR emission, possibly from SNR (Aharonian et al. 2005) - Zhang et al. (2008) find similar results from broad-band evolutionary model (slightly higher B, lower U dust )

Heidelberg 2008 Patrick Slane (CfA) 6 arcmin MSH Contains PWN powered by energetic pulsar B ( Edot = erg s -1 ) - complex nebula, with arcs, time-varying clumps, and bright jet extending to SE HESS observations reveal emission with extended morphology following jet - similar morphology to x-ray synchrotron emission suggests leptonic origin - IC model requires B~17  G and an anomalously high energy density in dust IR emission, possibly from SNR (Aharonian et al. 2005) - Zhang et al. (2008) find similar results from broad-band evolutionary model (slightly higher B, lower U dust ) Zhang et al. 2008

Heidelberg 2008 Patrick Slane (CfA) PWNe and Their SNRs ISM Shocked ISM Shocked EjectaUnshocked Ejecta PWN Pulsar Wind Forward Shock Reverse Shock PWN Shock Pulsar Termination Shock Pulsar Wind - sweeps up ejecta; shock decelerates flow, accelerates particles; PWN forms Supernova Remnant - sweeps up ISM; reverse shock heats ejecta; ultimately compresses PWN; particles accelerated at forward shock generate magnetic turbulence; other particles scatter off this and receive additional acceleration Gaensler & Slane 2006

Heidelberg 2008 Patrick Slane (CfA) HESS J arcmin Lemiere et al Extended source identified in HESS GPS - no known pulsar associated with source - may be associated with SNR G XMM observations (Funk et al. 2007) identify extended X-ray emission, securing an associated X-ray PWN Chandra observations (Lemiere et al. 2008) reveal point source within extended nebula, apparently identifying associated neutron star - HI absorption indicates a distance d ~ 8 – 13 kpc - L x ~ erg s -1  Edot ~ erg s -1 - X-ray and TeV spectrum well-described by leptonic model with B ~ 6  G and t ~ 15 kyr

Heidelberg 2008 Patrick Slane (CfA) 1 deg HESS J de Jager & Djannati-Atai 2008 XMMG Gaensler et al Discovered as part of HESS Galactic Plane survey - large diameter (~1 deg) which makes this an exceptionally large PWN ( R = 8.7 d kpc pc) unless it is very nearby (which, it apparently is not because…) Apparently associated with PSR B , whose DM distance is 4.12 kpc - G is known PWN associated with pulsar; asymmetric morphology suggests reverse shock interaction (Gaensler et al. 2003) - TeV emission shows same basic asymmetry on much larger scale; TeV-emitting electrons have lower energy than X-ray electrons  very low magnetic field See talk by M. Renaud

Heidelberg 2008 Patrick Slane (CfA) HESS J TeV spectral index steepens w/ increasing radius - effects of IC/synchrotron cooling HESS J appears to be a very extended PWN living in a large, unseen, old SNR that has evolved in a non-uniform ISM (causing reverse shock to displace PWN from position of pulsar) - may indicate a class of PWNe with low-energy electrons observable only (pardoxically) in TeV  -rays!

Heidelberg 2008 Patrick Slane (CfA) Vela X is the PWN produced by the Vela pulsar - located primarily south of pulsar - apparently the result of relic PWN being disturbed by asymmetric passage of the SNR reverse shock Elongated “cocoon-like” hard X-ray structure extends southward of pulsar - clearly identified by HESS as an extended VHE structure - this is not the pulsar jet (which is known to be directed to NW); presumably the result of reverse shock interaction Vela X van der Swaluw, Downes, & Keegan 2003 t = 10,000 yrt = 20,000 yrt = 30,000 yrt = 56,000 yr Blondin et al. 2001

Heidelberg 2008 Patrick Slane (CfA) Vela X LaMassa et al XMM spectrum shows nonthermal and ejecta-rich thermal emission from end of cocoon - reverse-shock crushed PWN and mixed in ejecta? Radio, X-ray, and  -ray measurements appear consistent with synchrotron and I-C emission from power law particle spectrum w/ two spectral breaks - density derived from thermal emission 10x lower than needed for pion-production to provide observed  -ray flux - much larger X-ray coverage of Vela X is required to fully understand structure

Heidelberg 2008 Patrick Slane (CfA) Vela X de Jager et al Radio and VHE spectrum for entire PWN suggests presence of two distinct electron populations - radio-emitting particles may be relic population; higher energy electrons injected by pulsar Maximum energy of radio-emitting electrons not well-constrained - this population will generate IC emission in GLAST band; spectral features will identify indentify emission from dintinct up-scattered photon populations - upcoming observations will provide strong constraints on this electron population

Heidelberg 2008 Patrick Slane (CfA) G : Another Reverse-Shock Interaction Temim et al G is a composite SNR with a bright central nebula - nebula is offset from SNR center - “finger” of emission extends toward northwest X-ray observations reveal compact source at tip of radio finger - trail of emission extends into nebula - L x suggests Edot ~ erg s -1 Compact X-ray emission is extended; presumably pulsar torus - PWN has apparently been disturbed by SNR reverse shock, and is now re-forming around pulsar, much like Vela X et al. Curious prong-like structures extend in direction opposite the relic PWN - these prongs appear to connect to a bubble blown by the pulsar in the SNR interior, apparently in the region recently crossed by the reverse shock; ANY TEV EMISSION?

Heidelberg 2008 Patrick Slane (CfA) G : Another Reverse-Shock Interaction Temim et al G is a composite SNR with a bright central nebula - nebula is offset from SNR center - “finger” of emission extends toward northwest X-ray observations reveal compact source at tip of radio finger - trail of emission extends into nebula - L x suggests Edot ~ erg s -1 Compact X-ray emission is extended; presumably pulsar torus - PWN has apparently been disturbed by SNR reverse shock, and is now re-forming around pulsar, much like Vela X et al. Curious prong-like structures extend in direction opposite the relic PWN - these prongs appear to connect to a bubble blown by the pulsar in the SNR interior, apparently in the region recently crossed by the reverse shock; ANY TEV EMISSION?

Heidelberg 2008 Patrick Slane (CfA) Conclusions PWNe are reservoirs of energetic particles injected from pulsar - synchrotron and inverse-Compton emission places strong constraints on the underlying particle spectrum and magnetic field Modeling of broadband emission constrains evolution of particles and B field - modeling form of injection spectrum and full evolution of particles still in its infancy Reverse-shock interactions between SNR and PWNe distort nebula and may explain TeV sources offset from pulsars - multiwavelength observations needed to secure this scenario (e.g. Vela X. HESS J , and others) Low-field, old PWNe may fade from X-ray view, but still be detectable sources of TeV emission - VHE  -ray surveys are likely to continue uncovering new members of this class