1 / 23

Understanding Pulsar Wind Nebulae: Expansion, Particle Flow, and Broadband Emission

Explore the dynamics of pulsar wind nebulae, including expansion, particle flow, and the mechanisms behind their broadband emission. Investigate the injection process and the impact of magnetic fields on synchrotron and inverse-Compton emission.

vtravis
Télécharger la présentation

Understanding Pulsar Wind Nebulae: Expansion, Particle Flow, and Broadband Emission

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Pulsar Wind Nebulae

  2. + G + + + + F R Pulsar Wind Nebulae b • Expansion boundary condition at • forces wind termination shock at • - wind goes from v = c/31/2 inside Rw to • v ~ RN/t at outer boundary } Pulsar logarithmic radial scale • Pulsar wind is confined by pressure • in nebula • - wind termination shock Wind MHD Shock Blast Wave  Particle Flow Ha or ejecta shell • Pulsar accelerates • particle wind - spectral break at where synchrotron lifetime of particles equals SNR age - radial spectral variation from burn-off of high energy particles • wind inflates bubble • of particles and • magnetic flux • particle flow in B-field • creates synchrotron • nebula Slane et al. 2004

  3. Broadband Emission from PWNe Zhang et al. 2008 • 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)

  4. Broadband Emission from PWNe Del Zanna et al. 2006 • 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 Volpi et al. 2008 See also talk by O.C. de Jager

  5. Connecting the Synchrotron and IC Emission • Energetic electrons in PWNe produce both synchrotron and inverse-Compton emission • - for electrons with energy ETeV, • synchrotron • inverse-Compton • - comparing photon energies from given electron • population gives B (e.g. Atoyan & Aharonian 1999) • Similarly, relative fluxes fE = E2 f(E) = nSngive B: • For low B, synchrotron lifetime is long, and fic/fs is large • - can expect bright TeV emission from collection of long-lived electrons; could explain • (some of the?) “dark” sources

  6. 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 Slane et al. 2004

  7. 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 Nebula Synchrotron Break Flux Density Injection E

  8. 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 VLA IRAC 4.5m Bietenholz 2006 Chandra IRAC 3.6m Slane et al. 2004 Slane et al. 2008

  9. 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 Slane et al. 2008

  10. 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 PRELIMINARY

  11. MSH 15-52 • Contains PWN powered by energetic • pulsar B1509-58 (Edot = 1037.3erg 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 mG 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 Udust)

  12. MSH 15-52 Aharonian et al. 2005 • Contains PWN powered by energetic • pulsar B1509-58 (Edot = 1037.3erg 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 mG 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 Udust) 6 arcmin

  13. MSH 15-52 • Contains PWN powered by energetic • pulsar B1509-58 (Edot = 1037.3erg 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 mG 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 Udust) 6 arcmin Zhang et al. 2008

  14. Reverse Shock PWN Shock Forward Shock Pulsar Termination Shock Pulsar Wind Unshocked Ejecta Shocked Ejecta Shocked ISM PWN ISM PWNe and Their SNRs • 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

  15. HESS J1640-465 Lemiere et al. 2008 5 arcmin • Extended source identified in HESS GPS • - no known pulsar associated with source • - may be associated with SNR G338.3-0.0 • 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 • - Lx ~ 1033.1erg s-1 Edot ~ 1036.7erg s-1 • - X-ray and TeV spectrum well-described by leptonic model with B ~ 6 mG and t ~ 15 kyr

  16. HESS J1825-137 1 deg G18.0-0.7 XMM de Jager & Djannati-Atai 2008 Gaensler et al. 2003 • Discovered as part of HESS Galactic Plane survey • - large diameter (~1 deg) which makes this an exceptionally large PWN (R = 8.7 dkpc pc) • unless it is very nearby (which, it apparently is not because…) • Apparently associated with PSR B1823-13, whose DM distance is 4.12 kpc • - G18.0-0.7 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

  17. HESS J1825-137 • TeV spectral index steepens w/ increasing radius • - effects of IC/synchrotron cooling • HESS J1825-137 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 g-rays!

  18. Vela X t = 10,000 yr t = 20,000 yr t = 30,000 yr t = 56,000 yr Blondin et al. 2001 van der Swaluw, Downes, & Keegan 2003 • 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

  19. Vela X LaMassa et al. 2008 • 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 g-ray flux • - much larger X-ray coverage of Vela X is required to fully understand structure

  20. Vela X de Jager et al. 2008 • 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

  21. G327.1-1.1: Another Reverse-Shock Interaction • G327.1-1.1 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 • - Lx suggests Edot ~ 1037.3 erg s-1 Temim et al. 2008 • 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?

  22. G327.1-1.1: Another Reverse-Shock Interaction Temim et al. 2008 • G327.1-1.1 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 • - Lx suggests Edot ~ 1037.3 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?

  23. 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 J1825-137, and others) • Low-field, old PWNe may fade from X-ray view, but still be detectable sources • of TeV emission • - VHE g-ray surveys are likely to continue uncovering new members of this class

More Related