Crab Pulsar. Chandra Image of the Crab Nebula. Crab is the most famous pulsar, which is studied in detail across the entire energy spectrum

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2 Crab Pulsar Chandra Image of the Crab Nebula Crab is the most famous pulsar, which is studied in detail across the entire energy spectrum

3 Conventional view on the Crab Pulsar Related Emitting Zones Pulsar(Massaro+) PWN(Aharonian&Atoyan) There are a few bright emissions sites, which are related to each other, but characterized by very different conditions

4 Non-Thermal Radiation of Pulsar

5 Non-Thermal Radiation of Pulsar Intuitive simplification Particles rapidly damp the perpendicular motion

6 Curvature Radiation

7 Curvature Radiation Radiation Scenario Particles move along magnetic field lines Radiation is caused by the B- field line bending

8 Curvature Radiation Radiation Scenario Particles move along magnetic field lines Radiation is caused by the B- field line bending Prediction High energy exponential cut-off

9 Curvature Radiation REVISITED (Kelner&Aharonian, 2012) Intuitive simplification Particles rapidly damp the perpendicular motion Intuitive simplification is WRONG c 2 1 = p2 v 2 +m2 c 2 p 2 p = p mc p 2 +m 2 c 2 = const

10 Curvature Radiation REVISITED (Kelner&Aharonian, 2012) Results In case of large initial pitch-angles to the magnetic field line, one should expect synchrotron emission In case of small pitch-angles There is a special trajectory around magnetic field line (smooth trajectory), which is characterized by conventional curvature radiation (i.e. provides a strict definition of the curvature radiation) When the particles move close to the smooth trajectory, the emitted spectrum differs from the one predicted by the conventional theory

11 Curvature Radiation REVISITED (Kelner&Aharonian, 2012) Spectra: Curvature vs small Pitch-Angle Case P ζ ( (ω/ω ) 1/3 ζ 1/3) 2 e u, ω where u = 3 2 ζ 1/3 (ω/ω ) 2/3 ζ 2/3 (ω/ω ) 1/ ζ

12 Curvature Radiation REVISITED (Kelner&Aharonian, 2012) P ζ ( (ω/ω ) 1/3 ζ 1/3) 2 e u, ω where u = 3 2 ζ 1/3 (ω/ω ) 2/3 ζ 2/3 (ω/ω ) 1/ ζ Fermi Measurements: P e (ω/ω )0.4 (e.g. Buehler, 2012) Fermi spectra deviates from the exponential cut-off for many pulsars

13 Curvature Radiation REVISITED (Kelner&Aharonian, 2012) P ζ ω ( (ω/ω ) 1/3 ζ 1/3) 2 e u, where u = 3 2 ζ 1/3 (ω/ω ) 2/3 ζ 2/3 (ω/ω ) 1/ ζ VHE Pulsed Signal: Power-Law? (MAGIC and VERITAS) Is these measurements are inconsistent with the obtained results? CONSISTENT

14 VHE observations of the Crab pulsar MAGIC Collaboration(2008) Veritas Collaboration(2011) MAGIC Collaboration(2011) Currently there is a general agreement between different experiments regarding the detection of the pulsed VHE emission from the Crab pulsar

15 Where is the pulsed VHE emission produced? It was predicted that the pulsar can also emit potentially detectable emission, which under certain conditions can be pulsed Signal produced by cold pulsar wind (Bogovalov&Aharonian, 2001)

16 Pulsar Nebula is a colorimeter of the wind Pulsar Related Emitting Zones Pulsar(Massaro+) PWN(Aharonian&Atoyan) Wind is not expected to emit any obvious radiation component, however it is possible to infer its properties through the non-thermal emission of the nebula

17 Kennel&Coroniti1984 Sketch of the model Pulsar wind Total Luminosity L w erg/s Bulk Lorentz Factor Γ w Wind Magnetization σ D MHD model by Kennel&Coroniti favored an ultrarelativistic weakly magnetized wind

18 2D numerical modeling of the Crab nebula Crab Nebula Del Zanna+2006 A few groups achieved a very impressive progress in 2D modeling of the Crab nebula: Amato, Bucciantini, Del Zanna+; Komissarov+; Bogovalov+

19 What is the pulsar wind Pulsar and Nebula 1D MHD Bulk Lorentz Factor Γ w 10 6 Wind Magnetization σ D MHD Bulk Lorentz Factor (?) Wind Magnetization σ 10 2 The properties of pulsar winds are not yet firmly established, however the requirement of ultrarelativistic wind apparently remains unavoidable

20 Bulk Comptonization of the wind Sketch of the scenario (Aharonian+2012) If the pulsar wind is accelerated enough close to the magnetosphere, a quite strong IC emission can be generated

21 Is the wind IC emission pulsed? Sketch of the scenario (Aharonian+2012) The X- and gamma-ray signals are perfectly synchronized if the wind is formed NOT very close to the pulsar

22 Inverse Compton interaction angle is determined from the first principles (Bogovalov&Aharonian2001) Energy Angular Momentum losses of pulsar: Ė sd = ΩṀsd Energy carried by an electron: Γ w mc 2 Angular Momentum carried by an electron: Γ w mr v Pulsar wind trajectory (if σ 1 ): r = c Ω = R L It is plausible that during the acceleration stage the wind trajectories are bended leading to a non-zero IC interaction angle

23 Spectrum can be explained SED accounting for the wind signal (Aharonian+2012) The flux level appears to depend strongly on the both model parameters: wind formation distance and wind Lorentz factor

24 Is the wind IC emission pulsed? Sketch of the scenario (Aharonian+2012) The X- and gamma-ray signals are perfectly synchronized if the wind is formed NOT very close to the pulsar

25 Wind signal lightcurve Light Curve (Aharonian+2012) Although the VHE lightcurve is consistent with the data points if the wind is formed not very close to the pulsar, the ratio of the lightcurve peaks indicates on presence of some wind anisotropy

26 Is it possible to measure the properties of the wind? Wind density reconstruction Current VHE data imply a large uncertainty for the density profile of the pulsar wind

27 Spectrum can be explained SED accounting for the wind signal (Aharonian+2012) The inferred wind bulk Lorentz factor appeared to match perfectly the value introduced by Kennel&Coronity to explain the optical-to-gamma emission of the nebula

28 Pulsar Wind Nebula Synchrotron and IC emission components (Aharonian&Atoyan, 1998)

29 Radio Emitting Electrons It is well known that Kennel&Coronity model cannot selfconsistently explain the radio spectrum detected from the Crab Nebula (e.g. Atoyan, 2000) However, it is important to distinguish two different constraints: the number of the available electrons, and their energy distribution The pulsar has injected into the nebula an amount of electrons sufficient to produce the radio emission, if Γ w B 1 0.1mG > i.e., the inferred wind Lorentz factor allows to inject enough electrons if B 200µG Although, a re-acceleration of these electrons is required

30 High Energy Part of the Spectrum EGRET Excess (Atoyan&Aharonian, 1996)

31 High Energy Part of the Spectrum MeV Dip (Aharonian&Atoyan, 1998)

32 High Energy Part of the Spectrum Crab Flare (Buehler+2012)

33 Summary We still don t understand Crab Complex Many problems wait for their solution, and...some others need to be revisited (also because of the improved quality of the observational data)