PARTICLE ACCELERATION IN ASTROPHYSICAL SOURCES Elena Amato INAF-Osservatorio Astrofisico di Arcetri.
-
Upload
janelle-water -
Category
Documents
-
view
217 -
download
1
Transcript of PARTICLE ACCELERATION IN ASTROPHYSICAL SOURCES Elena Amato INAF-Osservatorio Astrofisico di Arcetri.
ACCELERATED PARTICLES IN THE COSMOS
Sub-GeV
GALACTIC
EXTRAGALACTIC
~EeV
CERN
LHC (1
4 T
eV)
FIN
AL T
EVATRO
N (2
TeV)
E-2.7/3
ENERGETIC REQUIREMENTS
1 eV/cm3
CERN
LHC (1
4 T
eV)
FIN
AL T
EVATRO
N (2
TeV)
E-2.7/3
LARGE ENERGY DENSITY:EQUIPARTITION
WITHB-FIELD AND THERMAL GAS
LCR~3x1040 erg s-1
~0.1 x 1051erg x 3x10-10s-1
ESN RSN
SUPERNOVA REMNANTPARADIGM
(Baade & Zwicky 1934)
RELATIVISTIC PROTONS IN SNRS?
RX J1713.7
TeV EMISSION DETECTED!
SN 1006
NEUTRAL PION-DECAYOR
INVERSE COMPTON SCATTERING
OF ELECTRONS?
DETAILED SPECTRALMODELING REQUIRED!
CONCLUSION UNCERTAIN
IN MOST CASESBUT….
EVIDENCE FOR RELATIVISTIC PROTONS
W44
“PION BUMP” IN MIDDLE AGED SNRs INTERACTING WITH
MOLECULAR CLOUDS Fermi (Abdo+ 09,10; Ackerman+ 13) & Agile
(Giuliani+ 10,11; Cardillo+ 14)
Cardillo+ 14
IC443
NOT VERY
ENERGETIC PROTONS THOUGH….
SUPERNOVA REMNANTS PARADIGM
CERN
LHC (1
4 T
eV)
FIN
AL T
EVATRO
N (2
TeV)
E-2.7/3
Cas A
TychoMUST BE PEVATRONS
FERMI ACCELERATION MECHANISM
PARTICLE GAINS ENERGYEACH TIME IT CROSSES THE
SHOCK
PARTICLE GAINS ENERGY SOMETIMES
LOSES ENERGY SOME OTHERSAVERAGE ENERGY GAIN
ENERGY GAIN PER CYCLEV
UPSTREAMDOWNSTREAM
V-v2
FROM UPSTREAM FROM DOWNSTREAM
V-v2
RETURN PROBABILITY INDEPENDENT OF E
POWER LAW ENERGY SPECTRA ONLY DEPENDENT ON COMPRESSION RATIO
STRONG SHOCKS: u1/u2=4 p=4 e=2
PARTICLE ISOTROPIZATION
IF B SAME RESPONSIBLE FOR CR CONFINEMENT IN THE GALAXY: Emax~GeV
IF B ~B0, Emax~103-104 GeV (Lagage & Cesarsky 83)
•AMPLIFIED B IS REQUIRED TO REACH THE KNEE
COLLISIONLESS PLASMA…WAVE-PARTICLE INTERACTIONS!!!
INTERACTIONS MOST EFFICIENT AT RESONANCE
ACCELERATION TIME DEPENDS ONTURBULENCE LEVEL
MAXIMUM ACHIEVABLE ENERGY DEPENDS ON TURBULENCE LEVEL
->SPATIAL DIFFUSION
PITCH ANGLE DIFFUSION:
PARTICLE DIFFUSION AND WAVE GROWTH
IF CR ARE ISOTROPIZED BY THE WAVES…
MOMENTUM HAS GONE TO THE WAVES
BEFORE SCATTERING: PCR=nCRmCRvd
AFTER SCATTERING: PCR=nCRmCRvA
FOR RESONANT ALFVÉN WAVES
with
SUPERALFVÉNIC STREAMING OF CRs WAVE GROWTH
IN ADDITION 10% EFFICIENCY SHOCK MODIFICATION!!!!
EFFICIENT ACCELERATION AT SNR SHOCKS
CR STREAMING INDUCES PRESSURE GRADIENT UPSTREAM A PRECURSOR IS FORMED: FLUID PROGRESSIVELY SLOWS DOWN CR ESCAPE MAKES SHOCK RADIATIVE
RTOT>4 WHILE RSUB<4
CR PRECURSOR
SUBSHOCK
DENSITY OF ACCELERATED PARTICLES
DIFFERENT ENERGY PARTICLES HAVE DIFFERENT DIFFUSION LENGTHSEXPERIENCE DIFFERENT R (<4 AT LOW EN, >4 AT HIGH EN)
SPECTRUM BECOMES CONCAVE (STEEP AT LOW EN. FLAT AT HIGH)
BASIC PREDICTIONS OF NL-DSA
COMPRESSION RATIO > 4:
CD VS SHOCK IN TYCHO (Warren+ 05)
AND SN1006 (Cassam-Chenaii+ 08) AND
EMISSION PROFILES (Morlino+ 10)
T2 IS LOWER THAN EXPECTED: IN RCW86
T2~1/10 TRH (Helder+ 09, Morlino+ 13)
CONCAVE SPECTRA: RADIO SNRs (Reynolds & Ellison 92)
AND SED FITTING OF SN1006 AND RCW86 (Vink 12)
B-FIELD LARGELY AMPLIFIED
Blasi, Gabici, Vannoni 05
BACK-REACTION OF CRs MAGNETIC FIELD
AMPLIFICATION BACK-REACTION OF AMPLIFIED
FIELDTWO-FLUIDS: Drury & co.MONTECARLO: Ellison & co.FINITE DIFFERENCE: Berezhko, Volk & co.KINETIC: Amato & Blasi 05,06; Blasi+ 08Caprioli+ 08,09,10,11HINTS OF EFFICIENT
ACCELERATION:
AMPLIFIED MAGNETIC FIELDS
B~100-300G
IN THE SIMPLEST PICTURE
EFFICIENT PARTICLE ACCELERATION BECAUSE OF HIGH B-FIELD
HIGH B-FIELD BECAUSE OF EFFICIENT PARTICLE ACCELERATION
CAVEAT: LARGE MAGNETIC FIELDS MIGHT HAVE DIFFERENT ORIGINAND DO NOT IMPLY EFFICIENT SCATTERING…
Cas A Tycho
CR AMPLIFIED FIELDS“STANDARD” GROWTH RATE
ONLY APPLIES WHEN
OTHERWISE GROWTH OF RESONANT MODES IS SUPPRESSEDNON RESONANT MODES (Bell 04, Amato & Blasi 09) BECOME DOMINANT
CR CURRENT INDUCES COMPENSATING CURRENT IN PLASMA
INDUCES TRANSVERSE
PLASMA MOTION
RESULTING CURRENT ACTS AS A SOURCE OF B
FOR RIGHT-HAND POLARIZED WAVES, FIELD LINES ARE STRETCHED: FIELD IS AMPLIFIED
VERY LARGE FIELD ON VERY SMALL SCALES
EFFICIENT FOR SCATTERING?
SATURATION & SCATTERING • B-FIELD EASILY AMPLIFIED TO FEW X 100 G (Riquelme &
Spitkovsky 09, Caprioli & Spitkovsky 14)
• BUT SCATTERING IN SMALL SCALE TURBULENCE -> D(p)p2 ONLY EXTREME SNRS REACH THE KNEE (Zirakashvili & Ptuskin 08)
• BUT BELL’S TURBULENCE MIGHT SEED A DYNAMO (Bykov+13)
• NUMERICAL WORK (Caprioli & Spitkovsky 14): SCALE INDEED GROWS QUICKLY AND SCATTERING IS IN BOHM REGIME
EFFICIENT FIELD AMPLIFICATION ALSO HELPS RECONCILING OBSERVEDSPECTRA WITH OBSERVATIONS (Zirakashvili & Ptuskin 08, Caprioli 11)
SELF-REGULATING ACCELERATION AND ESCAPE
LITTLE TURBULENCE
LARGE CURRENT
LARGE ESCAPE FRACTION
TURBULENCE INCREASES
CURRENT DECREASES
EFFICIENT ACCELERATION
STEEPENING THE SOURCE SPECTRA…
Caprioli 11
Morlino & Caprioli 11
TYCHO
• THEORY PREDICTS FLATTER THAN 2 • GAMMA RAYS SHOW STEEPER THAN 2
CAVEAT: DEPENDS ON DETAILS OF THE TURBULENCE PROPERTIES MIGHT EVENFLATTEN THE SPECTRA
FOR SLOW SHOCK PARTIAL IONIZATIONSTEEPENS SPECTRA (Morlino+ 13, 14)
SEEING A PEVATRON
HOWEVER ONE COULD SEE ESCAPED PeV
PARTICLES FOR MUCH LONGER
(Gabici & Aharonian 07)
HARD TO SEE
Gallant, Amato, Lavalle in prep.
WITH UPCOMING TELESCOPES
POSSIBLE TO CHECK ON CAS A
PEVATRONS: EXTREME TYPE II FOR FEW X10 YR
Schure & Bell 13
A PEVATRON WE SEE…SYNCHROTRON AND ICS RADIATION
BY RELATIVISTIC PARTICLES
IN INTENSE (>few x 100 BISM) ORDERED
(HIGH POLARIZATION, IN RADIO, OPTICAL AND EVEN -RAYS, Dean et
al 08) MAGNETIC FIELD
SOURCE OF B FIELD AND PARTICLES:NS SUGGESTED
BEFORE PSR DISCOVERY
(Pacini 67)
Atoyan & Aharonian 96
PeV ELECTRONS
A PULSARS AND THEIR WINDS
PRIMARY CHARGES EMIT Υ-RAYS AND PAIR PRODUCE:
LARGE MULTIPLICTY ~104-108
ROTATING CONDUCTING MAGNET SURFACE ELECTRIC FIELD EXTRACTS CHARGES
A DENSE RELATIVISTIC WIND
MAINLY MADE OF PAIRS (THOUGH MAYBE PeV
IONS…)AND A TOROIDAL B-FIELD
LEAVES THE STAR:LORENTZ FACTOR ~ 104-FEW X 106THE MOST RELATIVISTIC
OUTFLOW IN NATUREAND THE MOST EFFICIENT ACCELERATOR KNOWN!!!
PULSAR WIND NEBULAE • WIND IS CONFINED BY
SURROUNDING SNR (OR ISM IN OLDER SYSTEM)
• WIND MUST SLOW DOWN TO MATCH SNR EXPANSION SPEED
• THIS HAPPENS THROUGH A SHOCK TRANSITION
Kes 75 (Chandra)
(Gavriil et al., 2008)
Gaensler & Slane 2006
RELATIVISTIC SHOCKS IN ASTROPHYSICS
Cyg ASS433
Crab Nebula
AGNs ~a few tensMQSs ~a few
PWNe ~104-106 GRBs ~102
PARTICLE ACCELERATIONTHE PW TERMINATION SHOCK IS COLLISIONLESS
MECHANIMSMS FOR DISSIPATION AND ACCELERATION DEPEND ON FLOW
•COMPOSITION(e--e+-p?)•MAGNETIZATION (=B2/4nmc2)
•GEOMETRY ( (B·n))
•COMPOSITION: MOSTLY PAIRS BY NUMBER BUT….
•MAGNETIZATION:DYNAMICS -> >10-2 FOR MOST OF THE FLOW•GEOMETRY: TRANSVERSE
PROPOSED MECHANISMS:FERMI MECHANISM IF/WHERE MAGNETIZATION IS LOW
ENOUGHDRIVEN MAGNETIC RECONNECTION AT THE SHOCK
(Lyubarsky 03, Lyubarsky & Liverts 08, Sironi & Spitkovsky 11)RESONANT CYCLOTRON ABSORPTION IN ION DOPED
PLASMA
(Hoshino et Al 92, Amato & Arons 06)
FERMI PROCESS AT RELATIVISTIC PAIR SHOCKS
EFFICIENT ACCELERATION AT UNMAGNETIZED SHOCKSNO ACCELERATION AT SUPERLUMINAL SHOCKS
NOT EVEN FERMI PROCESS AT LARGE OBLIQUITIES…SAME CONCLUSIONS FOR ELECTRON-ION SHOCKS….
RESULTS FROM PIC SIMULATIONS BY
Spitkovsky 08,Sironi & Spitkovsky 09, 11
DRIVEN MAGNETIC RECONNECTION
(Sironi & Spitkovsky 11)
REQUIRED K>107
BROAD PARTICLE SPECTRA WITH
=-(1-1.5)JUST RIGHT FOR
PWN RADIO EMISSION
BUT
RECONNECTION BEFORE THE SHOCK?
(Kirk & Skjaeraasen 03)
Drifting e+-e--pplasma
Plasma starts
gyrating
B increases
Configuration at the leading edge~ cold ring in momentum space
Coherent gyration leads tocollective emission of cyclotron waves
Pairs thermalize tokT~mec2 over 10-100 (1/ce)
Ions take their time:mi/me times longer
RESONANT CYCLOTRON ABSORPTION IN ION DOPED PLASMA
Magnetic reflection mediates the transition
ACCELERATION EFFICIENCY:
~few% for Ui/Utot~60% ~30% for Ui/Utot~80%
SPECTRAL SLOPE:>3 for Ui/Utot~60% <2 for Ui/Utot~80%
MAXIMUM ENERGY:~20% mic2 for
Ui/Utot~60% ~80% mic2 for
Ui/Utot~80%
PARTICLE SPECTRA AND ACCELERATION EFFICIENCY
•IONS CARRY MOST OF THE ENERGY: <mi/me
•WIND SUFFICIENTLY COLD: u/u<me/mi
RESULTS BY Amato & Arons 06 RECENTLY CONFIRMED BY Stockem et al 12
IF
NEUTRINOS? (Amato et al 03)
SUMMARY• PARTICLE ACCELERATION AT SNR SHOCKS IS A SELF-
REGULATING PROCESS WELL DESCRIBED BY NLDSA THEORY
• ACCELERATION UP TO THE “KNEE” LIKELY POSSIBLE FOR A SHORT TIME AFTER THE SN EXPLOSION
• NO EVIDENCE YET FOR PEVATRONS AMONG SNRs BUT HOPES FOR THE NEAR FUTURE
• PeV ELECTRONS ARE SEEN IN PWNe: THE CRAB NEBULA IS THE MOST EFFICIENT ACCELERATOR DIRECTLY OBSERVED IN NATURE!
• THE MAIN ACCELERATION PROCESS IS NOT FULLY UNDERSTOOD
• THE PRESENCE OF PEV IONS COULD PROVIDE A POSSIBLE SOLUTION TO THIS PUZZLE