Observational Constraints on Electron Heating at Collisionless Shocks in Supernova Remnants
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Observational Constraints on Electron Heating at Collisionless Shocks in Supernova Remnants
Cara Rakowski NRL
J. Martin Laming NRL
Parviz Ghavamian STScI
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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
Raymond et al. 2003, ApJ 584, 770
Cygnus Loop
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Ghavamian et al. 2002, ApJ 572, 888
Hbroad H
narrow H
H
HH
Hα narrow and broad components
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Ghavamian et al. 2002, ApJ 572, 888
Hbroad H
narrow H
H
HH
Hα narrow and broad components
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Ghavamian et al. 2002, ApJ 572, 888
broad H
narrow H
H
HH
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
• V FWHM, broad → Tp
• IB/IN → σx, σi → Te, Tp
(Chevalier, Kirshner & Raymond 1980 ApJ 235, 186)
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Te/Tp = 0.1
Te/Tp = 0.5
Te/Tp = 1.0
IB/IN (vshock, Te/Tp)
van Adelsberg, Heng, McCray & Raymond astro-ph/0803.2521v3
optically thick Lyman α vshock = 635 km s-1
Ghavamian et al. 2001 ApJ 547, 995
electron impact excitation and ionization are peaked
functions of Te
decreasing charge exchange at high velocities
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VFWHM,broad(Te/Tp, vshock)
van Adelsberg, Heng, McCray & Raymond astro-ph/0803.2521v3
At high vshock most protons are too fast to charge exchange, limiting further broadening.
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MA for 3G 105K 1cm-3 50% neutral gas
(Te/Tp)0 (1/vs2)
Tp vs2
Te=constant
Ghavamian, Laming & Rakowski, 2007 ApJ 654, L69
Results from Hα observations of Supernova Remnants
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more sophisticated treatment of post-charge exchange distribution functions
van Adelsberg, Heng, McCray & Raymond astro-ph/0803.2521v3
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cosmic ray lower hybrid waves
upstream rest frame
vs
k||2/k
2 me/mp
B
vgroup vsvphase
2=e p (e,p eB/me,pc)
L~ /vs
t= /vs2
meve2 = meD||t
D|| Bvs2 (E2)
meve2 B
1/Bheating independent of heating independent of
both vboth vss and B! and B!
1 ───
2
1 ───
2
1 ───
2
e ─
p+
Ghavamian, Laming, & Rakowski 2007Figure 2
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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)
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extra slides
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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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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:
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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
perpendicular Figure 3
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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
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Ultimate Goal: detect SEPs by their effect on thermal electrons
Multi-slit instantaneous EUV/UV Spectra
1.8 2.0 2.4 2.7
Mission Concept: see poster Newmark et al. SP43A-07
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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
Chianti simulated SOCS spectra
UVCS spectrum from Raymond et al 2000, sees
wings from shock heated ions
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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