PULSARS AND PULSAR WIND NEBULAE

Transcription

1 PULSARS AND PULSAR WIND NEBULAE Lecture 1 Elena Amato INAF-Osservatorio Astrofisico di Arcetri

2 OUTLINE LECTURE 1 INTEREST FOR ASTROPARTICLE PHYSICS PULSAR THEORY: CHARGE EXTRACTION, PAIR PRODUCTION, FORMATION OF A WIND GLOBAL ENERGY LOSSES, GAMMA-RAY EMISSION LATEST ADVANCES AND CHALLENGES PULSAR WIND NEBULAE BASIC INFERECES FROM SYNCHROTRON THEORY EVOLUTIONARY ONE-ZONE MODELS CHALLENGES LECTURE 2 MHD MODELING OF NEBULAE AND THEIR RADIATION 1-D MHD MODELING 2-D MHD MODELING VARIABILITY PARTICLE ACCELERATION AT THE MOST RELATIVISTIC SHOCKS IN NATURE OLD NEBULAE, FAST PULSARS AND THE ELECTRON-POSITRON EXCESS IN COSMIC RAYS

3 INTRODUCTION PULSAR WIND NEBULAE & PULSARS God s Hand B

4 WHY ARE PULSARS INTERESTING? MATTER IN EXTREME CONDITIONS BEST KNOWN COSMIC CLOCKS PRIMARY SOURCES OF ANTIMATTER IN THE GALAXY EXCELLENT LABS TO TEST GENERAL RELATIVITY AMONG THE FEW OBJECTS IN THE GALAXY WITH POTENTIAL DROPS IN EXCESS OF 1 PeV

5 WHY ARE PWNe INTERESTING? They enclose most of the pulsar spin-down energy: pulsed emission really is the tip of the iceberg Best-suited laboratories for the physics of relativistic astrophysical plasmas: close to c and close to us Particle acceleration at the highest speed shocks in Nature (10 4 < <10 7 ): a formidable challenge As many positrons as electrons:something to do with Pamela excess? Only sources showing direct evidence for PeV particles

6 THE PERFECT TIME TO STUDY THESE OBJECTS

7 HESS AND Fermi ERA High Energy Stereoscopic System ENERGY RANGE: Hess Victor 100 GeV<E <100 TeV Nobel Prize 1936 ANGULAR RESOLUTION: ~1 ENERGY RANGE: 100 MeV < E <300 GeV ANGULAR RESOLUTION: ~30 Fermi Enrico Nobel Prize 1938

8 THE GOLDEN AGE OF PSRs -Raywith Pulsars New Fermi Known LAT Before Pulsars Fermi Gamma Only MSP Radio+Gamma

9 UPDATED. QuickTime and a decompressor are needed to see this picture.

10 THE PULSING GeV SKY Pulses at 1/10 th true rate

11 THE NEBULOUS TeV SKY More than 1/2 of HESS sources associated with PWNe

12 PULSARS

13 DISCOVERY Bell and Hewish 1967 (Nobel 1974) IMPULSE WITH P1.33S LASTING 1/100 S D<cT POINTS TO PLANET WHITE DWARF? TOO FAST!!!

14 NEUTRON STARS PREDICTED IN THE 30s (Baade & Zwicky) AS FINAL PRODUCTS OF STELLAR COLLAPSE R 10km R 2 const 10 3 Hz BR 2 const B G ASSOCIATION PROVEN!!! CRAB PULSAR PREDICTED 1967 (Pacini) DETECTED 1968 (Staelin & Reifenstein)

15 OBLIQUE ROTATING MAGNETIC DIPOLE QuickTime and a decompressor are needed to see this picture. THIS IS ALL IN VACUUM

16 NO VACUUM PHYSICS STAR IS AN EXCELLENT CONDUCTOR IF VACUUM OUTSIDE: WHERE BOUNDARY CONDITION AT STAR SURFACE FINITE SURFACE CHARGE DENSITY AND A LARGE FIELD TO EXTRACT IT

17 THE GOLDREICH AND JULIAN MAGNETOSPHERE CHARGES EXTRACTED UNTIL E-FIELD CONTINUOUS AT STAR SURFACE (Goldreich & Julian, 1969) THE PULSAR DEVELOPS A COROTATING MAGNETOSPHERE THROUGHOUT COROTATION REGION QuickTime and a decompressor are needed to see this picture. COROTATION ONLY POSSIBLE UNTIL v<c LIGHT CYLINDER

18 CHARGE DISTRIBUTION CHARGE DENSITY? GJ CHANGES SIGN WHERE LAST CLOSED FIELD LINE TANGENT TO R LC AT THE EQUATOR QuickTime and a decompressor are needed to see this picture.

19 THE WIND ZONE ACTS AS SOURCE OF TOROIDAL FIELD: B T COMPARABLE TO B P AT THE LIGHT CYLINDER AT LARGER DISTANCES FIELD LINES ARE OPEN: B P MONOPOLE LIKE QuickTime and a decompressor are needed to see this picture. TOROIDAL FIELD BECOMES DOMINANT ~SAME AS FOR OBLIQUE DIPOLE IN VACUUM

20 PULSAR SPIN DOWN MORE GENERALLY:. a n Ė I. ai n1 AFTER INTEGRATION Ė ai 0 n 1 1 t / 0 n 1 n1 (t) 0 1/(n1) t / 0 1n a(n 1) n=braking INDEX. n=3 FOR A DIPOLE FIELD AND <3 FOR OTHER CASES DERIVING n IMPLIES MEASURING d 2 P/dt 2 MEASURED FOR 4 PSRs ONLY: ALWAYS LESS THAN 3!!!!

21 P-Pdot DIAGRAM PULSAR CHARACTERISTIC AGE QuickTime and a decompressor are needed to see this picture. MORE CORRECTLY ALSO PROVIDES A MEASURE OF B *

22 POTENTIAL DIFFERENCE IN CRAB E max 60 PeV UNSCREENED POTENTIAL ACCELERATION TO E» KNEE FOR PSRs IS MEASURED DIRECTLY:

23 P-Pdot DIAGRAM QuickTime and a decompressor are needed to see this picture.

24 CHARGE-SEPARATED FLOW? NOT FOR LONG! CHARGE DENSITY IS (SMALLER) LARGER THAN GJ ON (UN)FAVOURABLY CURVED FIELD LINES EITHER VACUUM OR SPACE-CHARGE LIMITED GAPS CREATE

25 PAIR PRODUCTION SITES POLAR CAPS SLOT GAPS OUTER GAPS CLOSE TO STAR UNSCREENED E // DUE TO FIELD LINE CURVATURE VACUUM OR SCL SAME BUT ON POLAR CAP BOUNDARY MORE EXTENDED ALONG LAST CLOSED FIELD LINE AT R LC

26 PULSAR EMISSION AT DIFFERENT ENERGIES FERMI GAMMAS RESEMBLE OPTICAL VHE GAMMA RESEMBLE HARD X-RAYS

27 ORIGIN OF RADIATION AT DIFFERENT ENERGIES EGRET PULSARS QuickTime and a QuickTime decompressor and a are needed decompressor to see this picture. are needed to see this picture. RADIO: COHERENT FROM POLAR CAP FROM OPTICAL TO GAMMA-RAYS: CURVATURE FROM FURTHER OUT

28 POLAR CAPS VACUUM GAPS (Ruderman & Sutherland 75,.) - GJ GJ SPACE-CHARGE LIMITED (Arons & Scharlemann 79, ) - GJ << GJ e - Curvature or ICS on star X-rays (E>50 MeV) +Be + +e - primary ~10 7 secondary ~ HARD -RAY SPECTRA: E -1.5/-2 WITH SUPERXP. CUTOFF AT FEW GeV PAIR MULTIPLICITY:

29 FERMI RESULTS THE CRAB PULSAR SPECTRUM QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. POLAR CAPS EXCLUDED! EXTENDED EMISSION FROM UP TO A FEW R * REQUIRED

30 QuickTime and a SLOT GAPS VELA LIGHT-CURVE decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. ALTITUDE OF PFF VARIES WITH MAGNETIC COLATITUDE (Arons 83): E // DECREASES TOWARDS RIM PFF AT LARGER DISTANCE SPECIAL RELATIVISTIC EFFECTS LEAD TO CAUSTICS (Dyks & Rudack 03) CUTOFF IS EXPONENTIAL

31 OUTER GAPS TPC QuickTime and a decompressor are needed to see this picture. VELA Romani & Watters 10 OUTER GAP - GJ GJ QuickTime and a decompressor are needed to see this picture. (Cheng, Ho, Ruderman 86; Hirotani, Romani ) EXPONENTIAL CUTOFF MULTIPLICITY?

32 LATEST DEVELOPMENTS ON PULSAR -RAY EMISSION MAGIC & VERITAS RESULTS ON CRAB FORCE-FREE LIGHT CURVES PARADIGM SHIFT?

33 MAGIC & VERITAS EMISSION MUST COME FROM (Aliu et al 08, 11; Aleksic et al 11, 12) R>30-40R * AND PROBABLY CANNOT BE CURVATURE AT ALL

34 MAGIC & VERITAS QuickTime and a decompressor are needed to see this picture. SINGLE PARTICLE CURVATURE SPECTRUM HAS A BREAK MAXIMUM PARTICLE ENERGY IS LIMITED BY LOSSES CURVATURE RADIATION SPECTRUM MUST BREAK (Aliu et al 08, 11; Aleksic et al 11, 12) ICS PROPOSED AS AN ALTERNATIVE (Lyutikov, Otte, McCann 11, Aharonian et al 12)

35 NEW PROPOSALS REPROCESSING X-RAYS THROUGH ICS QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. (Lyutikov, Otte, McCann 11; Aharonian, Bogovalov, Khangulyan 12)

36 THE FORCE FREE MAGNETOSPHERE FIELD LINES IN THE PLANE FOR 60 0 INCLINATION QuickTime and a decompressor are needed to see this picture. INTENSITY OF B INTENSITY OF J Spitkovsky 08

37 FROM VACUUM TO FORCE-FREE MAGNETOSPHERE IS POPULATED WITH PAIRS!!!! MULTIPLICITY >10 4 REQUIRED FROM PWN OBSERVATIONS TPC GAPS BECOME LARGER (Bai & Spitkovsky 10) OG QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture.

38 WHY SHOULD FORCE-FREE BE BETTER? BECAUSE WE MEASURE VERY LARGE MULTIPLICITIES

39 FOLLOW THE ENERGY -RAYS (AND PULSED EMISSION IN GENERAL) IS NOT WHERE THE ENERGY GOES!!!!! L 10 2 E R ON THE OTHER HAND L radio E R L PWN 0.1E R THE PWN IS WHERE THE ENERGY GOES!!!!

40 CONSTRAINTS ON PAIR PRODUCTION THE PULSAR WIND ENERGY E R B 2 0 R c ds c 3 4 E B wind E R N GJ m c 2 wind 1 m i m N GJ R 02 p 2 c GJ 0 e s 1 2 P AT R LC IS VERY LARGE!!!! IN THE NEBULAE WE OBSERVE is very large (e.g <<10 6 in Crab) wind is very large (e.g <<10 6 in Crab)) n m e n i m i c 3 N B 2 N GJ 4 m eff n eff c 2 2 wind

41 WHAT IS? WHAT IS? OPEN QUESTIONS E R N GJ m c 2 wind IS IT IONS WHO CARRY THE RETURN CURRENT? WHAT IS wind? 1 m i m 1 NOTE: for wind =10 6 These would be PeV Protons or 30PeV Fe And dominate the energy DETAILED MODELING OF PWNE REQUIRED FOR QUANTITATIVE ANSWERS Qualitatively: is very large (e.g <<10 6 in Crab) No charge sep. wind is very is very large large (e.g <<10 6 in Crab) But must become small MHD

42 LEARNING FROM PWNe FIRST LESSON: A DENSE OUTFLOW SIMPLEST DESCRIPTION: FORCE FREE CLOSE TO THE STAR MHD FURTHER OUT

43 PULSAR WIND NEBULAE Plerions: Supernova Remnants with a center filled morphology Flat radio spectrum ( R <0.5) Very broad non-thermal emission spectrum (from radio to X-ray and even -rays) (~15 objects at TeV energies) Kes 75 (Chandra) (Gavriil et al., 2008)

44 THE PULSAR WIND NEBULA ONE OF BEST STUDIED OBJECTS IN THE UNIVERSE D=6000 lyr BIRTH=1054 A.C. Chaco Canyon Anasazi Painting Chinese astronomers and native americans: a guest star in Taurus, 4 times brighter than Venus at maximum visible during the day for 23 days and at night for 2 years

45 THE PULSAR WIND NEBULA PRIMARY EMISSION MECHANISM: SYNCHROTRON RADIATION BY RELATIVISTIC PARTICLES IN AN INTENSE (>FEW X 100 B ISM ) ORDERED (HIGH DEGREE OF RADIO POLARIZATION) MAGNETIC FIELD SOURCE OF BOTH MAGNETIC FIELD AND PARTICLES: NEUTRON STAR SUGGESTED BEFORE PULSAR DISCOVERY (Pacini 67)

46 BASIC PICTURE OF A PWN ELECTROMAGNETIC BRAKING OF FAST-SPINNING MAGNETIZED NS IF WIND IS EFFICIENTLY CONFINED BY SURROUNDING SNR MAGNETIZED RELATIVISTIC WIND STAR ROTATIONAL ENERGY VISIBLE AS NON-THERMAL EMISSION OF THE MAGNETIZED RELATIVISTIC PLASMA R N pulsar wind R TS Synchrotron bubble

47 MODELING OF PWNe BASIC ARGUMENTS 1-ZONE MODELING 1-D MAGNETOHYDRODYNAMICAL MODELING 2-D AXISYMMETRIC MHD MODELING

48 SYNCHROTRON RADIATION SPECTRUM N() k p P tot s L P tot 4 3 c T 2 2 B 2 8 P P tot () s P a 1 2 B 2 s () s () a 2 2 B

49 P SYNCHROTRON RADIATION a 1 2 B 2 s () s () a 2 2 B SPECTRUM SINGLE PARTICLE SPECTRUM POWER-LAW PARTICLE DISTRIBUTION S () max N()P ()d a 1 B 2 2 min max min k p ( s ())d ( s ()) ( 0 ) s, ( 0 ) ( 0 ) 2a 2 0 B ( 0 ) 2a B S sync () a 1 2 a (1) 2 k B 1 p 1 2 IN ORDER TO ESTIMATE K AND WE NEED TO KNOW B

50 ESTIMATES OF B IN NON-THERMAL SOURCES EQUIPARTITION OR MINIMUM ENERGY

51 N() k p min max W tot V B2 8 max min EQUIPARTITION N() mc 2 d V B2 8 max min k mc 2 1 p d W tot V B2 8 kmc2 2 p (2 p) (2 p) max min w part kmc 2 (2 p ) (2 p ) max min 2 p 0 c 2 B 1 2 S () c 1 2 c (1) 2 k B 1 k 2S (1) c 1 c B( 1) 2 w part 2S mc 2 B ( 1) max (1) c 1 c 2 (2 p)/ 2 (2 p)/ 2 min 2 p c 2 ( p2)/ 2 B ( p2)/ 2

52 EQUIPARTITION FIELD w part 2S mc 2 B ( 1) max (1) c 1 c 2 (2 p)/ 2 (2 p)/ 2 min 2 p c 2 ( p2)/ 2 B ( p2)/ 2 p 2 1 W part B ( p2)/ 2 B (1) B 3/ 2 4S mc 2 min 3 / 2 c 1 c 2 (21)/ 2 (21)/ 2 max 2 1 W tot V B V B B5 / 2 0 B min 6 W B W part B eq 8 2/ 7 W tot CAVEATS!!!! B2 8 B3 / 2 2 / 7

53 CAVEATS ON EQUIPARTITION SAME VOLUME AND HOMOGENEITY W tot V B2 8 B3 / 2 MIN AND MAX FREQ. NOT KNOWN IN GENERAL 4S mc 2 min 3 / 2 c 1 c 2 (21)/ 2 (21)/ 2 max 2 1 RADIO EMITTING PARTICLES MIGHT NOT CARRY MOST OF THE ENERGY WHY EQUIPARTITION OR MINIMUM ENERGY?

54 EQUIPARTITION FIELD IN CRAB RADIO EMITTING PARTICLES HAVE THEIR EMISSION CORRESPONDS TO NOTE: EVEN IF IONS ARE THERE, THEY CANNOT BE ENERGETICALLY DOMINANT

55 BUT IN ~SAME B, X-RAYS COME FROM PARTICLES CORRESPONDING TO SYNCHROTRON SOURCES EVOLVE WITH TIME X-RAY EMITTING PARTICLES HAVE SHORT SYNCHROTRON LIFETIMES MIGHT RADIO EMITTING PARTICLES BE FOSSILE?????

56 1-ZONE EVOLUTIONARY MODELS EVERYTHING IS SPATIALLY HOMOGENEOUS BUT TIME-DEPENDENT (Pacini & Salvati 73): CHANGING PULSAR INPUT, SYNCHROTRON AND ADIABATIC LOSSES OF PARTICLES AND FIELD ARE INCLUDED INJECTION SPECTRUM PER UNIT TIME AND ENERGY INTERVAL: J(E,t) k(t) E K(t) CONSERVATION OF PARTICLE NUMBER dn(e,t) de J(E i,t i )dt i de i N(E,t) E JE i ;t i (E i,e,t) t max i RELATION NEEDED de E i E BETWEEN E, E i, t i

57 SINGLE PARTICLE EVOLUTION de dt c 1B 2 (t)e 2 E 3 1 V(t) dv dt SYNCHROTRON AND ADIABATIC LOSSES V 1/ 3 E 2 de dt V 4 3 3E dv dt c 1B 2 (t)v 1 3 (t) d dt 1 EV 1 3 c 1 B 2 (t)v 1 3 (t) 1 EV 1 3 (t) 1 E i V 1 3 (t i ) t c 1 B2 (t, )V 1 3 (t, ) dt, t i t i E E i E 2 dlogv i dt i 1/ CONTAINS SEEKED RELATION BETWEEN 1 E, E i, t i E i E b (t i ) E b (t) c 1 B 2 (t) dlogv 1/ 3 dt 1 BREAK ENERGY: SYNCHROTRON AND ADIABATIC LOSSES EQUAL

58 MAGNETIC FIELD EVOLUTION dw B dt d dt B L(t) W B 3V(t) dv dt dr B 2 R 3 B 2 R 2 dt 6 BLt V (t) 4 3 R(t)3 W B db 2 dt CONSERVATION OF MAGNETIC FLUX! d B 2 R 4 6 B L t dt t B2 t R(t)3 R 3 4B 2 R 2 dr dt 6 BL t R(t) B 2 R 4 B 0 2 R B L(t)R(t)dt t t 0 Ė ai 0 n 1 1 t / 0 n 1 n1

59 MAGNETIC FIELD EVOLUTION B 2 R 4 B 0 2 R B t t 0 L(t)R(t)dt EXPANSION WITH CONSTANT VELOCITY CONSTANT ENERGY SUPPLY: t<< R(t) vt L(t) L 0 B 2 6 B L 0 vt 2 QuickTime and a decompressor are needed to see this picture. v 4 t 4 B(t) 6 BL 0 v 3 1/ 2 1 t EXPANSION WITH CONSTANT BR 2 =cost VELOCITY 6 B(t) B L 0 2 DECAYING ENERGY SUPPLY: t>> ( -1)( - 2)v 3 1/ 2 1 t 2

60 R(t) vt B(t) B 0 t a BACK TO THE PARTICLES 1 EV 1 3 (t) 1 E i V 1 3 (t i ) t c 1 B2 (t, )V 1 3 (t, ) dt, t i 1 Et 1 c 1 E i t i 2a B2 (t i ) B 2 (t) E b (t) CONSTANT ENERGY INPUT: a=1 t i E E it i 1 E 1 i E i 1 E it E 2 E b (t i ) E 2 t i E b (t)t i t i Et 2 E i 2E i EE b (t) 1 1 c 1 B 2 (t)t t 1/ 2 E 2E b (t) 1 1 E 2E b (t) BREAK WAS ONCE AT VERY LOW ENERGY INITIAL RADIO PARTICLES CANNOT 1

61 LOW ENERGY LIMIT t i Et E i 2 E i EE b (t) 1 1/ 2 E 2E b (t) 1 E 2E b (t) 1 t i E E it i 1 E i E 2 E b (t i ) 1 E i 1 E it E 2 t i E b (t)t i 1 E b (t) 1 c 1 B 2 (t)t t N(E,t) E<<E b OR E B :ADIABATIC LOSSES ONLY t i Et t i E i E E it i E t 2 E E JE i ;t i (E i,e,t) t max i de E i J(E,t) k(t) E E N(E,t) k t E E max E E i de i kte

62 HIGH ENERGY LIMIT E>E B : SYNCHROTRON LOSSES DOMINATE t i Et 2 E i 2E i EE b (t) 1 t i Et 2E i 2 2E i EE b (t) E 2E b (t) t i E E it i 1 E i E 2 E b (t i ) 1 1/ 2 1/ 2 E 2E b (t) E 2E b (t) 1 1 Et E i t i E E it i E 2 E 2E b (t) E i E b E b E 1 E i E b (t i ) 1 t i t t i E t ie b E 2 N(E,t) K E max E t E i i de i E N(E,t) kte b E 2 E max E E i de i kt E b E 2 E 1 1 N(E,t) kte b E SPECTRUM STEEPENS BY -1 RADIATION SPECTRUM BY -1/2

63 SYNCHROTRON BREAK S sync () a 1 2 a (1) 2 k B 1 PARTICLE SPECTRUM N(E,t) kte 1 N(E,t) kte b E E E E b E b p 1 2 RADIATION SPECTRUM ( 1)/ 2 S (,t) S (,t) / 2 b b 2 b c 2 BE 2 1 b c 2 B c 1 B 2 t b c 2 c B 3 t 2 c 2 c 1 a 1 (mc 2 ) 2 a 2 (mc 2 ) T c 9(mc 2 ) ec 2(mc 2 ) 3 MAGNETIC FIELD IN A SOURCE OF KNOWN AGE B c c 1 t 2 b 1/ G t 2 / 3 [kyr] b 1/ 3 [GHz]

64 THE CRAB NEBULA b Hz B 300G p p b Hz B 100G E p 1 E E b N 1 (E) k E b E ( p 1 1) E b E E 0 ( p E 2 p ) 1 0 E b E ( p 2 1) E 0 E E max E p 1 E E 0 ( p N 2 (E) k E 2 p ) 1 0 E p 2 E 0 E E b ( p E 2 p ) 1 0 E b E ( p 2 1) E b E E max TWO BREAKS BETWEEN RADIO AND GAMMA-RAYS: WHICH ONE IS SYNCHROTRON AND WHICH IS AGE? B 80G t 2 [kyr] b [GHz] 1/ 3

65 sync sync P P tot s () a 2 2 B ADD ICS s () a 1 2 B 2 s () p 1 2 S sync () a 1 2 a (1) 2 k B 1 ICS P P tot ICS c () 8a 1 2 U rad c () c () 3 2 T a 1 Tc 9 a e 3 2 2mc S ICS () 4a 1 (3 T ) (1) U rad k

66 EXAMPLE CASE E p 1 E E 0 ( p N(E) k E 2 p ) 1 0 E p 2 E 0 E E b ( p E 2 p ) 1 0 E b E ( p 2 1) E b E E max CHECK OUT RELATIVE NORMALIZATION p p Hz 0 (300) and 0 (3) b Hz 1 (300) and 0 (3) b Hz 1 (300) and 0 (3)

67 THE CRAB NEBULA AGAIN B 80G t 2 [kyr] b [GHz] 1/ 3 p 1 2 p 1 / 2 b B 300G p p b B 100G E p 1 E E b N 1 (E) k E b E ( p 1 1) E b E E 0 ( p E 2 p ) 1 0 E b E ( p 2 1) E 0 E E max E p 1 E E 0 ( p N 2 (E) k E 2 p ) 1 0 E p 2 E 0 E E b ( p E 2 p ) 1 0 E b E ( p 2 1) E b E E max ( p 21)/ 2 p 2 / 2 ( p 11)/ 2 QuickTime and a decompressor are needed to see this picture.

68 1-ZONE MODELS FOR THE PWN EVOLUTION v L(t) 1/2 c / v =cost w =L(t)/(dN/dt) Crab w ~5x10 4 c ~7x10 5 3C58 w ~3x10 4 c ~10 5 Bucciantini et al. in prep

69 INFERRED MULTIPLICITIES QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture.

70 PeV PARTICLES WE SAID. EGRET: max ~30 MeV Fermi: max ~100 MeV (Abdo et al 2010) GETTING CLOSE TO MAXIMUM AVAILABLE POTENTIAL DROP

71 -RAY FLARES AGILE (Tavani et al. 2011) and Fermi (Abdo et al. 2011) Feb. 2009: F/F~5.5; T~16d Sept. 2010: F/F~4; T~4d

72 THE BIG ONE! Buehler et al 12 QuickTime and a decompressor are needed to see this picture. APRIL 2011: A FACTOR OF 30 INCREASE IN LUMINOSITY DURATION~10 DAYS VARIABILITY TIME-SCALE~HOURS

73 FLARE SPECTRUM

74 t loss E 6 mc de /dt sync T B 2 t acc t loss max 3h 2 LOSS-LIMITED ACCELERATION eb 2mc 2 max t acc max E mc 2 de /dt acc e E c mc feb t acc D B u 2 f 9h 2 cr L c 2 mc eb f 1 1 f 6e f B T B 100G e 2 mc T 230 f MeV NOTE: ALREADY FERMI STEADY IS CHALLENGING!!!! EXOTIC ACCELERATION PHYSICS?

75 WHAT CAN HELP. E-FIELDS LARGER THAN B-FIELD (LIKE IN RECONNECTION LAYERS) RELATIVISTIC BOOSTING: HELPS WITH CUT-OFF FREQUENCY AND TIME-SCALES MORE TOMORROW. MHD MODELING PARTICLE ACCELERATION MECHANISMS SOURCES OF VARIABILITY IN PWNE AND THEIR TIME-SCALES