PARTICLE ACCELERATION AND RADIATION IN PULSAR WIND NEBULAE Elena Amato INAF-Osservatorio Astrofisico di Arcetri Collaborators: Jonathan Arons, Niccolo’ Bucciantini, Luca Del Zanna, Barbara Olmi, Delia Volpi

PULSAR WIND NEBULAE AT A GLANCE PLERIONS: SUPERNOVA REMNANTS WITH A CENTER FILLED MORPHOLOGY FLAT RADIO SPECTRUM (R<0.5) VERY BROAD NON-THERMAL EMISSION SPECTRUM (FROM RADIO TO MULTI-TEV -RAYS) Kes 75 (Chandra) (Gavriil et al., 2008)

WHY PWNe ARE INTERESTING PULSAR PHYSICS: THEY ENCLOSE MOST OF THE PULSAR SPIN-DOWN ENERGY ( , , ) CLOSE AND BRIGHT: BEST-SUITED LABORATORIES FOR THE PHYSICS OF RELATIVISTIC ASTROPHYSICAL PLASMAS PARTICLE ACCELERATION AT THE HIGHEST SPEED SHOCKS IN NATURE (104<<107) COSMIC RAYS: ONLY SOURCES SHOWING DIRECT EVIDENCE FOR PEV PARTICLES ANTIMATTER STORAGE ROOMS: AS MANY POSITRONS AS ELECTRONS (PAMELA AND AMS02 EXCESS?)

THE CRAB NEBULA (WHERE WE HAVE LEARNT MOST OF WHAT WE KNOW) 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 Gaensler & Slane 2006 SOURCE OF B FIELD AND PARTICLES: NS SUGGESTED BEFORE PSR DISCOVERY (Pacini 67) Atoyan & Aharonian 96

MAIN OPEN QUESTIONS (personal view) WE KNOW THAT: THESE ARE THE MOST EFFICIENT ACCELERATORS OBSERVED IN NATURE AND ACCELERATION TAKES PLACE IN THE MOST HOSTILE ENVIRONMENT WE DO NOT KNOW: WHAT THE ACCELERATION MECHANISM(S) IS (ARE) POSSIBILITIES DEPEND ON: COMPOSITION (IONS? MULT.?) MAGNETIZATION (=B2/4nmc2) IN PRINCIPLE BOTH DEPEND ON WHERE PARTICLE ACCELERATION EXACTLY OCCURS HOW TO GET CONSTRAINTS? DETAILED DYNAMICAL AND RADIATION MODELING

PROPOSED ACCELERATION MECHANISMS FERMI MECHANISM: RIGHT SLOPE FOR OPTICAL/X-RAY PARTICLES VIABILITY DEPENDS ON PLASMA MAGNETIZATION (Spitkovsky 08, Sironi & Spitokvsky 11,12) RESONANT CYCLOTRON ABSORPTION IN ION DOPED OUTFLOW: MAGNETIZATION IS NOT VERY IMPORTANT REQUIRES IONS DOMINANCE PARTICLE SPECTRUM AND EFFICIENCY DEPEND ON FRACTION OF ENERGY CARRIED BY IONS (Hoshino et al 92, Amato & Arons 06, Stockem et al 12) DRIVEN MAGNETIC RECONNECTION: CORRECT SLOPE FOR RADIO PARTICLES REQUIRES EXTREMELY LARGE MULTIPLICITY DIFFICULT TO MAKE SELF-CONSISTENT (Lyubarsky 03, Lyubarsky & Liverts 08, Sironi & Spitkovsky 11)

CONSTRAINING THE WIND MAGNETIZATION AT THE SHOCK (Weisskopf et al 00) (Pavlov et al 01) Fsin2() Bsin() Lyubarsky 02 Bogovalov & Khangoulian 02

THE PULSAR WIND ANALYTIC SPLIT MONOPOLE SOLUTIONS (Michel 73; Bogovalov 99) CONFIRMED BY NUMERICAL STUDIES IN THE FORCE FREE (Contopoulos et al 99, Gruzinov 04, Spitkovsky 06) AND RMHD REGIME (Bogovalov 01, Komissarov 06, Bucciantini et al 06) Kirk et al 02 STREAMLINES ASYMPTOTICALLY RADIAL BEYOND RLC MAGNETIC FIELD COMPONENTS: Br1/r2 Bsin()/r MOST ENERGY FLOWS AT LOW LATITUDES: Fsin2() (Spitkovsky 06) WIND IS HIGHLY MAGNETIZED (>>1) CURRENT SHEET IN EQUATORIAL PLANE OSCILLATING AROUND EQUATOR IN OBLIQUE CASE ANGULAR EXTENT DEPENDS ON OBLIQUITY: MAGNETIC DISSIPATION?

JETS AND TORI AXISYMMETRIC RMHD SIMULATIONS OF PWNE (Weisskopf et al 00) JETS AND TORI Fsin2() Bsin()G() Lyubarsky 02 Bogovalov & Khangoulian 02 (Pavlov et al 01) AXISYMMETRIC RMHD SIMULATIONS OF PWNE Komissarov & Lyubarsky 03, 04 Del Zanna et al 04, 06 Bogovalov et al 05 Olmi et al 2014 Del Zanna et al 04

THE PHYSICS BEHIND THEM Velocity Magnetization Del Zanna et al 04 =0.03 FOR SUFFICIENTLY HIGH , EQUIPARTITION IS REACHED IN EQUATORIAL REGION EQUATORIAL FLOW IS DIVERTED TOWARDS HIGHER LATITUDES A FAST CHANNEL MAY THEN FORM ALONG THE AXIS

DEPENDENCE ON  OF FLOW VELOCITY (Del Zanna et al 04) =0.003 =0.03 BEST FIT : 10 X LARGER THAN WITHIN 1D MHD MODELING (Kennel & Coroniti 84) BUT STILL <<1 LOWER LIMIT ON : >0.01 REQUIRED FOR JET FORMATION =0.01

ISSUES WITH LOW  =0.025 =1.5 STEEP PARTICLE INJECTION SPECTRA: Mori et al 04: X2.2; Volpi et al 08: X2.7; Olmi+ 14: X2.9 LARGE NUMBER OF PARTICLES REVEALED BY ICS COMPONENT: Lsynne B2 , LICS ne Uph =0.025 LOW  LEADS TO LOWER B FIELD THAN REQUIRED TO FIT INTEGRATED SPECTRUM (Volpi et al 08, Olmi et al 14 vs Atoyan & Aharonian 96, de Jager & Harding 92) (Olmi et al 14) MAYBE  IS NOT THAT SMALL AFTER ALL =1.5 HOOP STRESSES DECREASED BY KINK INSTABILITIES (Begelman 98, Porth et al 13)

INCREASING … =1.5 =0.025 LOW  REQUIRED TO REPRODUCE HIGH ENERGY MORPHOLOGY

RECENT PROGRESS DIMENSIONALITY OF SIMULATIONS: IN 3D SAME  LOOKS VERY DIFFERENT! KINKS MAY MESS UP AND DISSIPATE FIELD IN THE PWN (Begelman 98) CONSEQUENCES ON SPECTRUM AND POLARIZATION??? BOTTOM LINE: CAN ONLY BE LARGER THAN INFERRED FROM 2D (Porth et al 13) SO WHAT?

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 (σ>0.001) SUPERLUMINAL SHOCKS

DIFFUSIVE SHOCK ACCELERATION IN WEIBEL MEDIATED (UNMAGNETIZED) e+-e- SHOCKS FERMI ACCELERATION EFFECTIVE (Spitkovsky 08) POWER LAW INDEX OK FOR THE OPTICAL/X-RAY SPECTRUM OF CRAB (Kirk et al 00) BUT e.g. VELA SHOWS FLATTER SPECTRUM (Kargaltsev & Pavlov 09) ONLY PARTICLES FROM REGIONS WITH 10-3 REST OF PARTICLES SMALL FRACTION OF THE FLOW SATISFIES LOW MAGNETIZATION (<10-3) CONDITION MOST OF THE FLOW HAS 0.1

RESONANT CYCLOTRON ABSORPTION IN ION DOPED PLASMA Configuration at the leading edge ~ cold ring in momentum space Magnetic reflection mediates the transition Coherent gyration leads to collective emission of cyclotron waves Drifting e+-e--p plasma B increases Pairs thermalize to kT~mec2 over 10-100 (1/ce) Ions take their time: mi/me times longer Plasma starts gyrating

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 RECENTLY CONFIRMED BY Stockem et al 12

Constraints on Crab wind parameters (Amato et al 03) Synchrotron from secondaries -rays from 0 decay OLD CALCULATION! TO BE REDONE FOR ICECUBE!

VARIABILITY WITHIN RCA RCA MECHANISM HAS AN INTRINSIC MAXIMUM ENERGY: BASED ON 1D PIC OF RCA (Amato & Arons 06) f~.1-.9 ( and Ei/Etot) Caveat: in 3D? FERMI STEADY CUT-OFF Tvar AND max IN THE BALLPARK FOR FIRST TWO, BUT THE BIG ONE… SPECIAL RELATIVITY COULD HELP:

DRIVEN MAGNETIC RECONNECTION BROAD PARTICLE SPECTRA WITH =-1.5 IF AND BUT REQUIRES K>107 RECONNECTION BEFORE THE SHOCK? (Kirk & Skjaeraasen 03) IF RADIO PARTICLES FROM HIGH LATITUDES LOWER K REQUIRED BUT STRIPES? (Sironi & Spitkovsky 11)

WIND COMPOSITION IF <mi/me IONS MAY CARRY MOST OF THE WIND ENERGY CYCLOTRON ABSORPTION COULD PROVIDE THE ACCELERATION NOTE: IN THE CASE OF CRAB THESE WOULD BE PeV IONS

THE PULSAR MULTIPLICITY N(g) g few 105 A BROKEN POWER-LAW ~1.5 ~104 k~106 FROM RADIO EMISSION (e.g. Bucciantini et al 11) ~2.2 ~3x106 k~104 FROM OPTICAL/X-RAY EMISSION (e.g. Kennel & Coroniti 84) A GJ DENSITY OF IONS, IF PRESENT, WOULD DOMINATE THE WIND ENERGY FLOW NO WAY FOR IONS TO BE ENERGETICALLY IMPORTANT EVEN IF THEY WERE THERE RADIO ELECTRONS MIGHT BE FOSSILE(Atoyan 99) OR ACCELERATED ELSEWHERE

RADIO EMISSION MORPHOLOGY SHOCK ACCELERATION + ADVECTION UNIFORM INJECTION VERY SIMILAR MAP Olmi et al 14

DIFFERENCE BETWEEN IMAGES AT RADIO WISPS MAGNETIC FIELD DIFFERENCE BETWEEN IMAGES AT DIFFERENT TIMES Olmi et al 14 Bietenholz et al 01 RADIO EMISSION TRACES MAGNETIC FIELD RADIO WISPS EVEN FOR UNIFORM PARTICLE DISTRIBUTION

ORIGIN OF RADIO PARTICLES =1.5 EMAX0.1-0.5 TeV 1<EMIN/mc2<103 10-6<n(cm-3)<10-4 PSR ORIGIN FOSSILE (Atoyan 99) WITH REACCELERATION NO CONSTRAINTS ON CURRENT K IF INJECTED AT LOW ENERGY NO VIOLATION OF ENERGY CONSTRAINTS EVAPORATION FROM THERMAL FILAMENTS (Bucciantini et al 11, Komissarov 13) ONLY e- IN THIS CASE: NO CONTRIBUTION TO e+ EXCESS (PAMELA: Adriani et al 09; AMS02: Aguilar et al 13; Blasi & Amato 11) BUT BOW SHOCK PWNe (Yusef-Zadeh & Gaensler 05, Ng et al 12)…. SPECTRAL CONTINUITY

WISPS AT MULTIWAVELENGTHS ISOTROPIC ACCELERATION OBSERVATIONS (Schweizer et al 13) Olmi et al in prep POLAR RADIO EQUATORIAL X

SUMMARY AND CONCLUSIONS PWNe ARE THE MOST EFFICIENT ACCELERATORS SEEN IN NATURE BUT PARTICLE ACCELERATION IN A VERY HOSTILE SETTING UNDERSTANDING THE ACCELERATION PHYSICS REQUIRES PINNING DOWN THE PLASMA PROPERTIES DETAILED DYNAMICS AND RADIATION MODELING ALLOWS TO SET LOWER LIMIT ON WIND MAGNETIZATION X-RAY EMITTING PAIRS MUST BE ACCELERATED IN HIGH  REGIONS: NO FERMI PROCESS AND MAGNETIC RECONNECTION SEEMS INCONSISTENT RADIO MORPHOLOGY DOES NOT ALLOW TO ASSESS THE ACCELERATION SITE OF RADIO PARTICLES ACCELERATION OF RADIO PARTICLES MAYBE UNRELATED TO WIND AND SHOCK CURRENT VALUE OF  MUCH LOWER ION DOMINATED WIND STILL POSSIBLE MULTIWAVELENGTH VARIABILITY OF INNER NEBULA SUGGESTS DIFFERENT ACCELERATION SITES IN DIFFERENT ENERGY RANGES OR TIME DEPENDENCE!