Observational Constraints on Electron Heating at Collisionless Shocks in Supernova Remnants

Cara Rakowski NRL

J. Martin Laming NRL

Parviz Ghavamian STScI

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

Ghavamian et al. 2002, ApJ 572, 888

Hbroad H

narrow H

H

HH

Hα narrow and broad components

Ghavamian et al. 2002, ApJ 572, 888

Hbroad H

narrow H

H

HH

Hα narrow and broad components

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)

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

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.

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

more sophisticated treatment of post-charge exchange distribution functions

van Adelsberg, Heng, McCray & Raymond astro-ph/0803.2521v3

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

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)

extra slides

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

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:

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

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

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

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

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