Transcript slides
PARTICLE ACCELERATION IN ASTROPHYSICAL SOURCES Elena Amato INAF-Osservatorio Astrofisico di Arcetri ACCELERATED PARTICLES IN THE COSMOS EXTRA GALACTIC GALACTIC E-2.7/3 Sub-GeV ~EeV ENERGETIC REQUIREMENTS 1 eV/cm3 LARGE ENERGY DENSITY: EQUIPARTITION WITH B-FIELD AND THERMAL GAS LCR~3x1040 erg s-1 ~0.1 x 1051erg ESN x 3x10-10s-1 RSN SUPERNOVA REMNANT PARADIGM (Baade & Zwicky 1934) E-2.7/3 SUPERNOVA REMNANTS Cas A RX J1713.7 RELATIVISTIC ELECTRONS SEEN THROUGH X-RAY EMISSION Tycho SN 1006 RELATIVISTIC PROTONS IN SNRS? TeV EMISSION DETECTED! NEUTRAL PION-DECAY OR INVERSE COMPTON SCATTERING OF ELECTRONS? RX J1713.7 DETAILED SPECTRAL MODELING REQUIRED! CONCLUSION UNCERTAIN IN MOST CASES BUT…. SN 1006 EVIDENCE FOR RELATIVISTIC PROTONS W44 Cardillo+ 14 “PION BUMP” IN MIDDLE AGED SNRs INTERACTING WITH MOLECULAR CLOUDS Fermi IC443 (Abdo+ 09,10; Ackerman+ 13) & Agile (Giuliani+ 10,11; Cardillo+ 14) NOT VERY ENERGETIC PROTONS THOUGH…. SUPERNOVA REMNANTS PARADIGM Cas A MUST BE PEVATRONS Tycho E-2.7/3 FERMI ACCELERATION MECHANISM PARTICLE GAINS ENERGY SOMETIMES LOSES ENERGY SOME OTHERS AVERAGE ENERGY GAIN DOWNSTREAM PARTICLE GAINS ENERGY EACH TIME IT CROSSES THE SHOCK UPSTREAM ENERGY GAIN PER CYCLE V RETURN PROBABILITY INDEPENDENT OF E POWER LAW ENERGY SPECTRA ONLY DEPENDENT ON COMPRESSION RATIO 3u1 -g N( p) µ p gp = p FROM UPSTREAM u1 - u2 FROM DOWNSTREAM STRONG SHOCKS: V-v2 V-v2 u1/u2=4 p=4 e=2 PARTICLE ISOTROPIZATION COLLISIONLESS PLASMA… WAVE-PARTICLE INTERACTIONS!!! PITCH ANGLE DIFFUSION: ->SPATIAL DIFFUSION INTERACTIONS MOST EFFICIENT AT RESONANCE ACCELERATION TIME DEPENDS ON TURBULENCE LEVEL MAXIMUM ACHIEVABLE ENERGY DEPENDS ON TURBULENCE LEVEL 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 PARTICLE DIFFUSION AND WAVE GROWTH IF CR ARE ISOTROPIZED BY THE WAVES… BEFORE SCATTERING: PCR=nCRmCRvd AFTER SCATTERING: PCR=nCRmCRvA * dPCR nCR mg CR (v d - v A ) = dt t FOR RESONANT ALFVÉN WAVES dPCR dPw 1 dE w 1 (dB) = = = 2g w dt dt v A dt vA 8p 2 with MOMENTUM HAS GONE TO THE WAVES * CR n æ eB ö = nCR ç p > ÷ è ck ø 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 SUBSHOCK CR PRECURSOR DENSITY OF ACCELERATED PARTICLES DIFFERENT ENERGY PARTICLES HAVE DIFFERENT DIFFUSION LENGTHS EXPERIENCE 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 BACK-REACTION OF CRs MAGNETIC FIELD AMPLIFICATION BACK-REACTION OF AMPLIFIED FIELD TWO-FLUIDS: Drury & co. MONTECARLO: Ellison & co. FINITE DIFFERENCE: Berezhko, Volk & co. KINETIC: Amato & Blasi 05,06; Blasi+ 08 Caprioli+ 08,09,10,11 HINTS OF EFFICIENT COMPRESSION RATIO > 4: ACCELERATION: 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 AMPLIFIED MAGNETIC FIELDS Tycho Cas A 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 ORIGIN AND DO NOT IMPLY EFFICIENT SCATTERING… CR AMPLIFIED FIELDS “STANDARD” GROWTH RATE ONLY APPLIES WHEN OTHERWISE GROWTH OF RESONANT MODES IS SUPPRESSED NON 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: 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 SELF-REGULATING ACCELERATION AND ESCAPE LITTLE TURBULENCE LARGE ESCAPE FRACTION LARGE CURRENT CURRENT DECREASES EFFICIENT ACCELERATION TURBULENCE INCREASES EFFICIENT FIELD AMPLIFICATION ALSO HELPS RECONCILING OBSERVED SPECTRA WITH OBSERVATIONS (Zirakashvili & Ptuskin 08, Caprioli 11) STEEPENING THE SOURCE SPECTRA… THEORY PREDICTS FLATTER THAN 2 • • GAMMA RAYS SHOW STEEPER THAN 2 r¢ = u1 + v ¢A,1 u2 + v ¢A,2 a= r¢ + 2 >2 r¢ -1 Caprioli 11 Morlino & Caprioli 11 TYCHO CAVEAT: DEPENDS ON DETAILS OF THE TURBULENCE PROPERTIES MIGHT EVEN FLATTEN THE SPECTRA FOR SLOW SHOCK PARTIAL IONIZATION STEEPENS SPECTRA (Morlino+ 13, 14) SEEING A PEVATRON Schure & Bell 13 PEVATRONS: EXTREME TYPE II FOR FEW X10 YR HOWEVER ONE COULD SEE ESCAPED PeV PARTICLES FOR MUCH LONGER (Gabici & Aharonian 07) WITH UPCOMING TELESCOPES POSSIBLE TO CHECK ON CAS A HARD TO SEE Gallant, Amato, Lavalle in prep. 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 PeV ELECTRONS SOURCE OF B FIELD AND PARTICLES: NS SUGGESTED BEFORE PSR DISCOVERY (Pacini 67) Atoyan & Aharonian 96 A PULSARS AND THEIR WINDS ROTATING CONDUCTING MAGNET SURFACE ELECTRIC FIELD EXTRACTS CHARGES PRIMARY CHARGES EMIT Υ-RAYS AND PAIR PRODUCE: LARGE MULTIPLICTY ~104-108 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 106 THE MOST RELATIVISTIC OUTFLOW IN NATURE AND 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 Gaensler & Slane 2006 Kes 75 (Chandra) (Gavriil et al., 2008) RELATIVISTIC SHOCKS IN ASTROPHYSICS AGNs ~a few tens MQSs ~a few SS433 GRBs ~102 Cyg A PWNe ~104-106 Crab Nebula PARTICLE ACCELERATION THE 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 ENOUGH DRIVEN 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 RESULTS FROM PIC SIMULATIONS BY Spitkovsky 08, Sironi & Spitkovsky 09, 11 EFFICIENT ACCELERATION AT UNMAGNETIZED SHOCKS NO ACCELERATION AT SUPERLUMINAL SHOCKS NOT EVEN FERMI PROCESS AT LARGE OBLIQUITIES… SAME CONCLUSIONS FOR ELECTRON-ION SHOCKS…. DRIVEN MAGNETIC RECONNECTION BROAD PARTICLE SPECTRA WITH =-(1-1.5) JUST RIGHT FOR PWN RADIO EMISSION BUT REQUIRED K>107 RECONNECTION BEFORE THE SHOCK? (Kirk & Skjaeraasen 03) (Sironi & Spitkovsky 11) RESONANT CYCLOTRON ABSORPTION IN ION DOPED PLASMA Configuration at the leading edge ~ cold ring in momentum space Magnetic reflection mediates the transition Drifting e+-e--p plasma B increases Coherent gyration leads to collective emission of cyclotron waves Pairs thermalize to kT~mec2 over 10-100 (1/ce) Plasma starts gyrating Ions take their time: mi/me times longer PARTICLE SPECTRA AND ACCELERATION EFFICIENCY IF •IONS CARRY MOST OF THE ENERGY: <mi/me •WIND SUFFICIENTLY COLD: u/u<me/mi 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% RESULTS BY Amato & Arons 06 NEUTRINOS? RECENTLY CONFIRMED BY Stockem et al 12 (Amato et al 03) SUMMARY • PARTICLE ACCELERATION AT SNR SHOCKS IS A SELFREGULATING 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