balmer-dominated supernova remnants and the physics of … · 2018. 4. 30. · supernova remnants...
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Balmer-Dominated Supernova Remnants and the Physics of
Collisionless Shocks
Parviz Ghavamian
SNR 0509-67.5HST ACS Hα (F657N)
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Supernova Remnants Heat and Enrich the ISM and Accelerate Cosmic Rays
blast wave (~5000 km s-1)(X-ray synchrotron radiation
from e- CRs ~ 10 TeV)
reverse-shocked Si-Rich and Fe-Rich SN ejectaT ~ 5×107 K
Remnant of SN 1572 (Tycho’s SNR)(CXC/NASA)
Bozkurt et al. (2013)
X-ray synchrotronin SW Tycho
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SNRs Are Believed to Generate Cosmic Rays Up to the Proton ‘Knee’ near 1015 eV
(Taylor 2016)
Unknown&Galactic&sources
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Why Study Supernova RemnantShocks?
I. They Accelerate Cosmic Rays
II. They are Collisionless Shocks, Whose Physics isPoorly Understood
III. These shocks occur in many places inastrophysics (Galaxy clusters, star formingregions, large scale structure formation…), sounderstanding them is important!
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The Shock Jump Conditions in a Plasma
T1, !1, B1T2, !2, B20
mj
shock front of thickness ∆d ~ ℓ mfp
v1
v2
B1 ∣∣
B1 ⊥
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Why Collisionless?
• Average distance a proton of velocity v (cm/s) travels before suffering a hard 90º deflection is
• For protons in a SNR shock, v ~ 2000-104 km s-1, and ni
~ 0.1-1.0 cm-3, so
100 L.Y. ≲ d90º ≲ 1000 L.Y. ~ ∆d ≫ RSNR
…Shock jump CANNOT be one collision mean free path!
• Instead, scattering and heating of charged particles atthe shock front occurs via plasma waves and MHDturbulence
(Spitzer 1962)L.Y.
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Quasi-Perpendicular Collisionless Shock
∆d ≈ rL,i= miv⊥ / eB
∆d
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Broad Physics of a Collisionless Shock
STREAM Kinetic Energy Entering Shock(e-s and ions in interstellar B-field)
Plasma Instabilities(2-stream, firehose, Weibel….)
Plasma Waves(Alfvén, lower hybrid, whistler)
Heating of Ions(resonant/non-resonant scattering of ions and e-s)
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Perpendicular Shocks Have Pre-Shock Wave Activity!
∆d
superthermalions
(the ‘foot’)
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• Electron and ion heating at shock transition dependson complicated microphysics of the plasma, so:
(me/mp) ≤ (Te / Tp)0 ≤ 1
• Observational probes of conditions in the immediatepostshock gas are needed
Degree of Electron-Ion (Ion-Ion) Temperature Equilibration is Unknown
minimal from jump cond(~ 1/1836 for e-, p)
maximum (efficient collisionless heating)
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(courtesy A. Spitkovsky) (relativistically correct shock speed)
mag
netiz
atio
n pa
ram
eter
Parameter Space of Collisionless Shocks
ΓvSH/c
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Blue+Green: X-rays (Chandra)Red: Hα
One Tool: Non-Radiative Shocks in Warm Partially Ionized Gas (Balmer-Dominated
Shocks)
SNR 0509-67.5(HST/ACS) SNR 0519-69.0 SNR 0505-67.9
(DEM L 71)(HST/WFC3)
Fe-rich ejecta
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Most Balmer-Dominated SNRs Result from Type Ia SNe (Detonation of a C/O or O/Ne WD)
Whelan & Iben (1973)Shen & Bildsten (2009)
Webbink (1984)Ilkov & Soker (2012)
Strömgren sphereLow Radiation Prior to Merger
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What Are Balmer-Dominated Shocks?
• Nonradiative shocks in warm, partially neutral ISM producespectra dominated by collisionally excited H I (T ~ 107-108 K)
e-, p
slow HI
fast HI
(Raymond et al. 2010)
pbroad
Hα, Hβ…
narrow Hα, Hβ… ∆vFHWM ~ 10-50 km/s
∆vFHWM � 1000 km/s
• Faint: nISM ~ 1 cm-3; only factor of 4 post-shock compression
• Hard to detect, requires deep narrowband Hα imagery
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Broad and Narrow Hα Emission is Sensitive to The Initial Electron-Ion Equilibration
broad and narrow H lines
(Te)0
(Tp)0
(FUV)100 - 200 nm
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dHI ≲ 10-4 pc
SN 1006: Edge-on Sheet Geometry
Winkler et al. (2009)
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15#yr&X#ray&Expansion&of&Tycho’s&SNR&(Chandra)
(1"3$keV$(soft$X"rays):&shows&thermal&emission&only)
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Tycho’s SNR: The Movie
Tycho’s SNR: 19-year baseline
Winkler, Blair & Fesen (KPNO 4m data)
Knot g
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Hα
3.0-5.0 keV0.3-1.0 keV
Ghavamian et al. (2013)
(P. F Winkler)(S. Park et al.
2007)
Balmer-Dominated Shocks
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Observables in Balmer-Dominated Spectra
SN 1006Nikolic et al. (2013): IFU obs.
∆VFWHM
SN 1006
∆V
∆VFWHM(Hα, Hβ,...) ∝ Tp, VSH
(Smith et al. 1991; G01, G02, G07, G13, van
Adelsberg et al. 2008)
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Tycho Knot g
Tycho NETycho NWKepler
SN 1006
SNR 0548-70.4
(DEM L71)
SNR 0519-69.0
RCW 86
(Te/Tp)0
Observing Many Balmer SNRs Reveals a Distinct Trend: (Te/Tp)0
van Adelsberg et al 2008; G13
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Cosmic Ray Acceleration
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A Possible Explanation For Te/Tp ∝ 1/VSH2
(T, n, B)
shock jump
∝ pCR(max)
vSH
• A constant heating ∆Ee wouldreproduce what we see
• Likely occurs ahead of the shock• Likely candidate: cosmic rayprecursor
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How to Get this Trend?One Possibility: Lower Hybrid (LH) in the CR Precursor
(G07; Rakowski et al. 2008)
(CR-driven Alfvén waves)
B⃑
• LH waves can bulk heat e-s parallel to δB • ∆Ee = ½me∆ve2 ∝ Ωe #CR
∆Ee ~ 0.3 keV (const)
δB⃑
LH waves:
δB⃑
ωLH = (Ωe Ωp)1/2
B⃑