1. 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

2. 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)

3. 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?)

4. 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

5. 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

6. 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)

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

8. 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/r 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?

9. 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

10. 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

11. 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

12. 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)

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

14. 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?

15. 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

16. 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

17. 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
(1/ce)
Ions take their time:
mi/me times longer
Plasma starts
gyrating

18. PARTICLE SPECTRA AND ACCELERATION EFFICIENCYIF
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

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

20. 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:

21. 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)

22. 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

23. THE PULSAR MULTIPLICITY
N(g) g
few 105
A BROKEN
POWER-LAW
~ ~ k~106
FROM RADIO EMISSION
(e.g. Bucciantini et al 11)
~ ~3x 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

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

25. 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

26. ORIGIN OF RADIO PARTICLES
= EMAX TeV 1<EMIN/mc2< <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

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

28. 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!