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O. de Jager, C. Venter, M. Vorster (NWU, S.A.)

North-West University, Potchefstroom

South Africa

Fundamental Problems: Pulsars to their WindsNS & GB – 30 March to 5 April:

Cairo & Alexandria

Primary acceleration fields (unscreened by pair production)

- ensemble average of pulsed gamma-ray emission from a globular cluster.
- Caviats: pair production in ms pulsars
- Pulsar Wind Nebulae probing pulsar properties:
- Birth periods from dynamics and MWL observations.
- Pair production multiplicities.
- Caviats: Stabbed PWN – Vela X

Select unscreened pulsars to test basic semi self consistent models for particle acceleration. Screening complicates matters.

- Average over a large sample of similar pulsars to obtain a statistical average over uncertain magnetic inclination and viewer line of sights.
- N=50 millisecond pulsars in 47 Tucanae Globular cluster provide an ideal sample.

Calculate 3D rotating model magnetospheres for sample of N=100 cluster ms pulsars in 47 Tuc with random P,Pdot.

- Take random observer & magnetic angles and calculate flux slices cut by observer.
- Follow escape of radiation reaction limited electrons through the light cylinder (about 1% of spindown power).

Venter & de Jager (2008) and

- Venter, de Jager & Clapson (2009), ApJL
- EoS and number N of pulsars main uncertainties.

Venter, de Jager & Clapson (2009), ApJL

- Shocked “Pulsar Winds” from ms pulsars?
- Assume Bohm diffusion in cluster. No re-acceleration assuming sigma parameter does not decrease beyond light cylinder. Also, no reacceleration in cluster space. Even HESS becomes constraining for 5 – 10 G cluster fields given N=50. However, if field lines in cluster are not tangled then diffusion faster than Bohm is possible and predicted unpulsed cluster flux should drop.

However, disaster !!! Look at the radio, X-ray and Fermi pulse profiles of ms pulsars !

Fermi Pulse profiles implies:

- Copious pair production:
- Field strength too low for magnetic pair production.
- However, photon-photon pair production
- Cascading – include synchrotron for X-rays
- Screening
- Slot gaps etc. to explain Fermi fan beams.
- Let us be self-critical and face our demons: Why did we predict Fermi a-priori correct within a factor 2 ?

Galactic Radio pulsar statistics (F-G & Kaspi 06):

- P0=0.3±0.15 s
- Pmin=0.01 s (SN157B in LMC)
- Millisecond Birth Period would destroy the SNR shell
- (1/2)I2 = 2E52 (1 ms/P)2 erg > ESN =1051 E51 erg
- Leptons ejected during spindown history give a relic wind. X-ray synchrotron emitting leptons would most likely burn away, but surviving lower energy leptons should give IC radiation gamma-ray nebula. Lack of such a nebula gives a lower limit on birth period.
- Estimating the Birth Period of Pulsars through GLAST LAT Observations of Their Wind Nebulae(O. C. de Jager 2008 ApJ)

Kes 75: MWL studies of SNRTotal number of leptons: Ne>8x1048 Integrated number of Goldreich Julian pairs: NGJ=1.6x1044Pair production multiplicity: 2.5x105 > M > 2.4x104

X-rays in annular rings measure flux & photon index vs. radius

- Connect profiles for radial flow velocity V(r) and radial field strength B(r) profile via Faraday’s induction equation.
- Assume spherical and planar (cylindrical) geometry, obtain trial (B,V) solutions coupled via Faraday.
- Free parameters at pulsar wind termination shock and downstream:
- Conversion efficiency of spindown power to leptons
- Field compression ratio
- Maximum lepton energy (constrained by gyroradius size)
- Sigma parameter
- Radial dependence of flow profile (depends on geometry)

Measurements of the sigma parameter and pulsar conversion efficiency in from Vela compact nebula from X-rays and MHD principles. How does that square up with HESS observations?

Solving 1D particle transport equation downstream including synchrotron & adiabatic losses. Synchronize grid with X-ray resolution.Calculate synchrotron spectra from lepton spectra

Model & observed spectral evolution vs. radius. Constrain to freshly injected compact nebula (30 years) – avoid outer regions of reverse shock.

What does it predict for HESS? Too little ! Because we see relic electrons accumulated over 11 kyr

Who pricked the bag of Vela X ?

- The total lepton energy from TeV (+ MWL) observations correspond to a conversion efficiency of 0.001 of spindown power to leptons.
- Estimate from X-rays is ~0.1 => factor 100 higher.
- Reverse shock could have punched the field line structure of the PWN => protective azimuthal configuration lost.
- Leptons leak out.
- How serious is this leakage problem for other post-reverse shock (Vela-like) HESS PWN ? Are they reliable calorimeters ? The pre-reverse shock HESS PWN (Crab-like) maintain their leptons.

Conclusions

- Galactic plane seems to be dotted with PWN along |b|0, where Type II SNR are typically formed following massive star formation in molecular clouds.
- Ground-based VHE gamma-ray observations probe the electron component of extended PWN, which corresponds to the EUV domain (in synchrotron), which cannot be done with EUV instruments (absorption).
- Target photon field for PWN is CMBR/galactic photons fields => spatial map of VHE emission truly reflects the electron distribution. Same cannot always be said about X-ray observations, due to
- Contamination from thermal emission and
- Possible gradients in the PWN magnetic field strength complicates conclusions about resident electron distributions.
- Energy dependent morphology is a proof of electron origin in G18.0-0.7. First detection of such morphology in HESS J1825-137.
- Particle dominated PWN are ideal VHE sources (de Jager & Venter 2005). This allow them to (a) have radiation maxima in IC rather than synchrotron, and (b) maximal expansion sizes from electron survival considerations.

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