PARTICLE ACCELERATION IN ASTROPHYSICAL SOURCES Elena Amato INAF-Osservatorio Astrofisico di Arcetri.

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)

SUPERNOVA REMNANTSTycho

RX J1713.7

SN 1006

Cas A

RELATIVISTIC ELECTRONSSEEN THROUGH X-RAY EMISSION

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