Pulsar Wind and pulsar wind nebulae

Transcription

1 Pulsar Wind and pulsar wind nebulae Takata Jumpei 1

2 Outline S1, Pulsar Wind (PW) and Pulsar Wind Nebula(PWN) around isolate pulsars. -PWN nebula around the Crab pulsar -Formation of PW and PWNe -Kennel & Coroniti model -CHANDRA images of PWNe -TeV emissions -Polarization S2, Pulsar wind around binary system -PSR B a Be star system 2

3 References Bucciniti N. Modeling Pulsar Wind Nebulae, 2008 Kargaltsev O., Pavlov G.G. Pulsar Wind Nebulae in the Chandra Era, 2008 de Jager O.C., Djannati-Atai A. Implications of H.E.S.S. observations of pulsar wind nebula, 2008 Dubus G., Binaries and GLAST, 2007 Gaensler B.M., Slane P., The evolution and Structure of Pulsar Wind Nebulae,

4 PW of isolated pulsrs 4

5 Pulsar wind nebula around the Crab pulsar Pulsar Inner ring -0.1pc (10arc s) -under luminous Pulsar Torus Jets Tourus and Jests -Synchrotron and I.C. Inner ring 5

6 Spectral energy distribution of the Crab PWN 1, Spectral peak energy 2,Luminosity TeV emissions 3,Equipartition condition ~10 6 B~ 0.1mG N ~1038 / s Pulsar supplies electrons and positrons 6

7 Pulsar wind formation In pulsar magnetosphere -formation of pulsar wind electrons/positrons. Ω Light cylinder Pair-creation ~1000km Beyond light cylinder -particles are cold (due to the radiation colling near the pulsar) - magnetic field is frozen in the flow. -pulsar wind carries pulsar spin down energy (5 10^38erg/s) 7

8 Pulsar Wind Nebula If PW interacts with ambient gases, a termination shock stands -Pulsar wind pressure = Ambient gas pressure 1/2 1/2 s,36 amb, 10 RTS ~0.05 E P pc (Inner ring) -Pulsar wind is being thermalized -Particles are accelerated at the shock 0.1pc PW (cold) Torus -Thermalized electrons/positrons emit the photons via Synchrotron and inverse-compton process ==> Pulsar Wind Nebula shock 8

9 Kennel & Coroniti (1984) Spherical symmetric Steady Ideal MHD Magnetic field components perpendicular flow direction PW (cold) shock (Thermalize) To shine as the Crab nebula, the energy of the relativistic bulk motion (dynamical energy) before the shock must go to thermal (internal) energy after the shock. = Electromagnetic energy flux Particle energy flux 9

10 Kennel & Coroniti (1984) L sp 6 ~10 1 B = 2 r s c 1 r s ~0.1pc L sp n1 = r s m e c 1 P 1=0 2 1 shock B1 P1 u1 n1 B2 P2 u2 n2 u1 B1 u2 B2 = Jump Condition 1 2 E B1 E B2 1 1 = n1 u 1 4 n1 u 1 P1 B 21 P2 B 22 1 u 1 = 2 u2 n1 u1 8 n1 u1 n1 u1 8 n1 u1 n 1 u 1=n 2 u 2 10

11 Internal energy vs. σ 1.0 Large sigma; weak shock Total energy -most of total energy is carried by as magnetic energy Mangetic energy Particle internal energy -Less efficiencient conversion from bulk motion (dynamics) energy to Dynamic energy thermal energy downstream 0.5 Small sigma (<<1); strong shock σ Efficient conversion 11

12 Atoyan & Aharonian (1996) =

13 MHD simulations = 0.03 Jet Torus Small sigma upstream flow produces polar jets (by hoop stress), and jet velocity (0.7c) consistent with the observation. Del Zanna et al

14 Sigma paradox Sigma must be very large near the pulsar. The energy conversion from magnetic to particle energy have to take place between the pulsar and the shock, so that from 1 near the pulsar to 1 at the shock Magnetic reconnection (Kirk 2005)? 14

15 Pulsar Wind Nebula with Chandra Thanks to spacial resolution of Chandra, 40PWNe (+14 candidates) have been identified. P-dot P 15

16 Crab B Vela B

17 B Geminga 17

18 18

19 PWNe and TeV H.E.S.S.=High Energy Stereoscopic System 18 out of 71 TeV sources are PWNe. 19

20 Crab PWN 1TeV electrons/positrons emit optical photons by synchrotron radiation and 1TeV photons by the IC process with CMB. Why is it point source? Is it IC origin? 20

21 Vela-X region 21

22 TeV emission mechanism PSR B

23 Hadronic Model Nakamori et al. (2008) Positrons Nuclei π+ π- π0 2γ 23

24 Leptonic Model electron X-ray B TeV CMB 24

25 Optical polarization map (CFHT) / = B-vector Polarization Optical Crab pulsar Optical (Hickson & Van Den Bergh 1990) Soft X-ray (Weisskopf et al., 1978) - 19% at ~160 25

26 Random fields? Nakamura & Shibata (2007) If magnetic fields has only toroidal components, the expected averaged polarization degree is about 50%. The observed values are explained, if 60% of the magnetic field energy are provided by the random fields. Energetically, the random field may dominate 26 the pure toroidal fileld.

27 Makishima et al 左の図の模式図 27

28 Questions Where and how the conversion from magnetic energy to particle energy are taken place? What is the composition of PW. - TeV emission mechanisms -Shock acceleration mechanism Polarization in higher energy bands. 28

29 PW of pulsar in binary systems 29

30 PSR B a Be star system PSR B ; P~48ms (pulsed radio) Be star; M~10Msun, R~10Rsun, T~40000K eccentricity~0.87, Po~3.4yr Periastron Rp~0.7AU and apastron Ra~10AU d~2kpc 30

31 Non-pulsed emissions From Radio and TeV emissions. Emissions from the pulsar wind particles accelerated at the shock, where the PW preesure is equal to the stellar wind pressure 31

32 Stellar wind -Polar wind -Dense equatorial wind Shock standing point 13 RTS ~5 10 cm 12 RTS ~5 10 cm Johnston et al periastron 32

33 apastron Light curves periastron Disk apastron Disk X-ray TeV Radio 33

34 Light curve; Flux vs. photon index (X-ray bands) 34

35 Previous studies Leptonic model (Tavani & Arons 1997, Kirk et al. 1996) Radio, X-ray ; synchrotron TeV; inverse Compton Hadronic model (Chernyakova et al. 2006) -Protons (ions) energy dominate in PW. TeV; π-zero decay loaded by protons in PW and stellar wind. Radio to X-ray; synchrotron and IC processes of pairs. 35

36 Problem Leptonic model - Why does TeV flux decrease around the periastron? Hadronic model - Why can we see the X-ray emissions at apastron? -Why is PW composition different from that of the Crab? Leptonic + Hadronic model? Light curve 36

37 Summary There are still many open questions about PW -sigma paradox -PW composition -PW TeV emission mechanisms -Magnetic structure in PW (polarization) Binary system is another way to study PW -Flux and photon index variations with orbital phases 37

38 38

39 sigma~0.003 Expansion speed of PWN as a function of radial distance is obtained by solving dynamics. R=20 shock radius, from optical σ=1 observation σ=0.1 σ=0.01 σ= Rs 39

40 40