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Observational Constraints on Electron Heating at Collisionless Shocks in Supernova Remnants

This study investigates the interactions of electrons in collisionless shocks within supernova remnants, focusing on Hα emission from shock fronts. The analysis covers both non-radiative and radiative shocks, detailing the emission lines (e.g., O III, N II, S II) from the recombination zones. Emphasis is placed on the role of hot electrons, their impact on hydrogen excitation, and the mechanisms driving temperature ratios between electrons and protons. The research utilizes observational data and models to explore cosmic ray interactions and electron heating in the context of shock dynamics.

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Observational Constraints on Electron Heating at Collisionless Shocks in Supernova Remnants

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  1. Observational Constraints on Electron Heating at Collisionless Shocks in Supernova Remnants Cara Rakowski NRL J. Martin Laming NRL Parviz Ghavamian STScI

  2. Hα emission from the shock front • Non-radiative shocks: primarily Hα emission from the immediate shock front • Radiative shocks: show O III, N II, S II etc from recombination zone downstream Cygnus Loop Raymond et al. 2003, ApJ 584, 770

  3. narrow H H H H broad H H Hα narrow and broad components Ghavamian et al. 2002, ApJ 572, 888

  4. narrow H H H H broad H H Hα narrow and broad components Ghavamian et al. 2002, ApJ 572, 888

  5. narrow H H H broad H H Hα narrow and broad components neutral H entering the shock: • excited by electrons or protons, emits narrow Hα • charge exchanges with shock heated protons creating hot neutrals that emit broad Hα • VFWHM, broad→ Tp • IB/IN→ σx, σi → Te, Tp (Chevalier, Kirshner & Raymond 1980 ApJ 235, 186) Ghavamian et al. 2002, ApJ 572, 888

  6. Te/Tp = 0.1 Te/Tp = 0.5 Te/Tp = 1.0 IB/IN (vshock, Te/Tp) electron impact excitation and ionization are peaked functions of Te decreasing charge exchange at high velocities optically thick Lyman α vshock = 635 km s-1 van Adelsberg, Heng, McCray & Raymond astro-ph/0803.2521v3 Ghavamian et al. 2001 ApJ 547, 995

  7. VFWHM,broad(Te/Tp, vshock) At high vshock most protons are too fast to charge exchange, limiting further broadening. van Adelsberg, Heng, McCray & Raymond astro-ph/0803.2521v3

  8. MAfor 3G 105K 1cm-3 50% neutral gas Results from Hα observations of Supernova Remnants (Te/Tp)0  (1/vs2) Tp  vs2 Te=constant Ghavamian, Laming & Rakowski, 2007 ApJ 654, L69

  9. more sophisticated treatment of post-charge exchange distribution functions van Adelsberg, Heng, McCray & Raymond astro-ph/0803.2521v3

  10. cosmic ray lower hybrid waves 2=e p (e,p eB/me,pc) L~  /vs t=  /vs2 meve2 = meD||t D|| Bvs2 (E2) meve2 B  1/B heating independent of both vs and B! B vgroup  vs vphase 1─── 2 1─── 2 k||2/k2 me/mp p+ vs 1─── 2 e ─ upstream rest frame Figure 2 Ghavamian, Laming, & Rakowski 2007

  11. Te/Tp v2shock, Teconstant? Lower hybrid waves (LHW) in a cosmic ray (CR) precursor • CR diffusion length scale for heating, and LHW vgroupvshock allows Te independent of vshock and B. • LHW growth requires some B w.r.t shock normal. • If B generated by B-field amplification, then at MA = 60 ---12, LHW growth will exceed modified Alfvén wave growth. Ghavamian, Laming & Rakowski, 2007 ApJ 654, L69 (first estimates) Rakowski, Laming & Ghavamian 2008 ApJ 684, 348 (kinetic growth rate)

  12. extra slides

  13. DEM L71, new long-slit spectra confirm IB/IN too low in most regions to be matched by current models. We suspect H is being ionized and excited by hot electrons in the CR precursor

  14. Growth Rate Comparison • lower hybrid wave kinetic growth rate • non-resonant modified Alfvén wave growth rate • maximum Alfvén wave growth rate • Mach number at which lower-hybrid waves grow faster than modified Alfvén waves for  shocks:

  15. Cosmic-ray precursor • non-resonant modified Alfvén waves amplify B • MA decreases near shock • lower-hybrid wave growth takes over, heating the resonant electrons parallel Figure 3 perpendicular

  16. Solar Wind Shocks • interplanetary bow shocks in the solar wind show a relationship closer to Te/Tp1/v . • this could be explained if the cosmic rays were non-relativistic picking up an extra factor of vs/c in the diffusion coefficient. Figure 4 data from Schwartz et al 1986

  17. Multi-slit instantaneous EUV/UV Spectra 2.0 1.8 2.7 2.4 Ultimate Goal: detect SEPs by their effect on thermal electrons Mission Concept: see poster Newmark et al. SP43A-07

  18. Ultimate Goal: detect SEPs by their effect on thermal electrons Predicting ground-level SEP events • Primary mission, detect seed particles prior to CME eruption available for acceleration to high energy SEPs • Simultaneously the O VI and He II lines can be modeled to determine the electron to ion temperature ratio to test for rapid electron heating indicative (under our model) of SEP generated lower-hybrid waves UVCS spectrum from Raymond et al 2000, sees wings from shock heated ions Chianti simulated SOCS spectra

  19. DEM L71, new long-slit spectra confirm IB/IN too low in most regions to be matched by current models. We suspect H is being ionized and excited by hot electrons in the CR precursor

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