Fundamental Problems:

Pulsars to their Winds O. de Jager, C. Venter, M. Vorster (NWU, S.A.) O. de Jager, C. Venter, M. Vorster (NWU, S.A.)

North-West University, PotchefstroomNorth-West University, PotchefstroomSouth Africa South Africa

NS & GB – 30 March to 5 April: NS & GB – 30 March to 5 April: Cairo & AlexandriaCairo & Alexandria

ContentsContents Primary acceleration fields Primary acceleration fields

(unscreened by pair production) (unscreened by pair production) – ensemble average of pulsed gamma-ensemble average of pulsed gamma-

ray emission from a globular cluster.ray emission from a globular cluster.– Caviats: pair production in ms pulsarsCaviats: pair production in ms pulsars

Pulsar Wind Nebulae probing pulsar Pulsar Wind Nebulae probing pulsar properties:properties:– Birth periods from dynamics and MWL Birth periods from dynamics and MWL

observations.observations.– Pair production multiplicities.Pair production multiplicities.– Caviats: Stabbed PWN – Vela XCaviats: Stabbed PWN – Vela X

How can we test first principles of How can we test first principles of pulsar electrodynamics pulsar electrodynamics

experimentally?experimentally? Select unscreened pulsars to test basic semi Select unscreened pulsars to test basic semi

self consistent models for particle self consistent models for particle acceleration. Screening complicates matters.acceleration. Screening complicates matters.

Average over a large sample of similar Average over a large sample of similar pulsars to obtain a pulsars to obtain a statistical average over statistical average over uncertain magnetic inclination and viewer uncertain magnetic inclination and viewer line of sightsline of sights..

N=50 millisecond pulsars in 47 Tucanae N=50 millisecond pulsars in 47 Tucanae Globular cluster provide an ideal sample.Globular cluster provide an ideal sample.

GR-Frame dragging model of Muslimov & GR-Frame dragging model of Muslimov & Harding. Magnetic inclination and EoS Harding. Magnetic inclination and EoS

enters as main uncertainty.enters as main uncertainty.

• 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).

Predicted pulsed flux Predicted pulsed flux within a factor 2 of Fermi within a factor 2 of Fermi

if we reduce N to 50.if we reduce N to 50.

• Venter & de Jager (2008) and • Venter, de Jager & Clapson

(2009), ApJL

• EoS and number N of pulsars main uncertainties.

Predicted unpulsed Predicted unpulsed nebular flux to be tested nebular flux to be tested

with CTA.with CTA.

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 However, disaster !!! Look at the radio, X-ray and Fermi the radio, X-ray and Fermi

pulse profiles of ms pulsars !pulse profiles of ms pulsars !

Implications:Implications: Fermi Pulse profiles implies:Fermi Pulse profiles implies: Copious pair production: Copious pair production:

– Field strength too low for magnetic pair Field strength too low for magnetic pair production.production.

– However, photon-photon pair productionHowever, photon-photon pair production– Cascading – include synchrotron for X-raysCascading – include synchrotron for X-rays– ScreeningScreening– Slot gaps etc. to explain Fermi fan beams.Slot gaps etc. to explain Fermi fan beams.

Let us be self-critical and face our Let us be self-critical and face our demons:demons: Why did we predict Fermi Why did we predict Fermi a-prioria-priori correct within a factor 2 ? correct within a factor 2 ?

At least three constraints on At least three constraints on pulsar birth periods.pulsar birth periods.

1.1. Galactic Radio pulsar statistics (F-G & Kaspi 06): Galactic Radio pulsar statistics (F-G & Kaspi 06): PP00=0.3±0.15 s=0.3±0.15 s PPminmin=0.01 s (SN157B in LMC)=0.01 s (SN157B in LMC)

2.2. Millisecond Birth Period would destroy the SNR shellMillisecond Birth Period would destroy the SNR shell (1/2)I(1/2)I22 = 2E52 (1 ms/P) = 2E52 (1 ms/P)22 erg > E erg > ESN SN =10=105151 E E5151 erg erg

3.3. Leptons ejected during spindown history give a relic Leptons ejected during spindown history give a relic wind. X-ray synchrotron emitting leptons would most wind. X-ray synchrotron emitting leptons would most likely burn away, but surviving lower energy leptons likely burn away, but surviving lower energy leptons should give IC radiation gamma-ray nebula. Lack of should give IC radiation gamma-ray nebula. Lack of such a nebula gives a lower limit on birth period. such a nebula gives a lower limit on birth period.

Estimating the Birth Period of Pulsars through Estimating the Birth Period of Pulsars through GLASTGLAST LAT Observations of Their Wind NebulaeLAT Observations of Their Wind Nebulae(O. C. de Jager 2008 (O. C. de Jager 2008 ApJ)ApJ)

Kes 75: MWL studies of SNRKes 75: MWL studies of SNR

Total number of leptons: NTotal number of leptons: Nee>8x10>8x1048 48

Integrated number of Goldreich Julian pairs: Integrated number of Goldreich Julian pairs: NNGJGJ=1.6x10=1.6x104444

Pair production multiplicity: 2.5x10Pair production multiplicity: 2.5x105 5 > M > 2.4x10> M > 2.4x1044

How reliable are these How reliable are these calorimetric calorimetric

measurements?measurements?

We will see that Vela X has been We will see that Vela X has been stabbed !stabbed !

Measurements of the sigma parameter and pulsar Measurements of the sigma parameter and pulsar conversion efficiency in from Vela compact nebula conversion efficiency in from Vela compact nebula

from X-rays and MHD principles. from X-rays and MHD principles. How does that square up with HESS observations?How does that square up with HESS observations?

• 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)

Zoom in on compact PWN: Pulsar/Torus/JetZoom in on compact PWN: Pulsar/Torus/Jet

Solving 1D particle transport equation downstream Solving 1D particle transport equation downstream including synchrotron & adiabatic losses. including synchrotron & adiabatic losses.

Synchronize grid with X-ray resolution.Synchronize grid with X-ray resolution.Calculate synchrotron spectra from lepton spectraCalculate synchrotron spectra from lepton spectra

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

Parameters for Vela X:Parameters for Vela X:

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

Vela Torus/Jet/PulsarVela Torus/Jet/PulsarREVERSE SHOCK

HESS detection of Vela X (Aharonian et al. 2006)

Who pricked the bag of Vela X ?Who pricked the bag of Vela X ?

The total lepton energy from TeV (+ MWL) The total lepton energy from TeV (+ MWL) observations correspond to a conversion observations correspond to a conversion efficiency of 0.001 of spindown power to leptons.efficiency of 0.001 of spindown power to leptons.

Estimate from X-rays is Estimate from X-rays is ~~0.1 => factor 100 0.1 => factor 100 higher.higher.

Reverse shock could have punched the field line Reverse shock could have punched the field line structure of the PWN => protective azimuthal structure of the PWN => protective azimuthal configuration lost.configuration lost.

Leptons leak out.Leptons leak out. How serious is this leakage problem for other How serious is this leakage problem for other

post-reverse shock (Vela-like) HESS PWN ? Are post-reverse shock (Vela-like) HESS PWN ? Are they reliable calorimeters ? The pre-reverse shock they reliable calorimeters ? The pre-reverse shock HESS PWN (Crab-like) maintain their leptons.HESS PWN (Crab-like) maintain their leptons.

ConclusionsConclusions Galactic plane seems to be dotted with PWN along |b|Galactic plane seems to be dotted with PWN along |b|0, where 0, where

Type II SNR are typically formed following massive star Type II SNR are typically formed following massive star formation in molecular clouds.formation in molecular clouds.

Ground-based VHE gamma-ray observations probe the electron Ground-based VHE gamma-ray observations probe the electron component of extended PWN, which corresponds to the EUV component of extended PWN, which corresponds to the EUV domain (in synchrotron), which cannot be done with EUV domain (in synchrotron), which cannot be done with EUV instruments (absorption).instruments (absorption).

Target photon field for PWN is CMBR/galactic photons fields => Target photon field for PWN is CMBR/galactic photons fields => spatial map of VHE emission truly reflects the electron spatial map of VHE emission truly reflects the electron distribution. Same cannot always be said about X-ray distribution. Same cannot always be said about X-ray observations, due toobservations, due to– Contamination from thermal emission andContamination from thermal emission and– Possible gradients in the PWN magnetic field strength Possible gradients in the PWN magnetic field strength

complicates conclusions about resident electron distributions.complicates conclusions about resident electron distributions. Energy dependent morphology is a proof of electron origin in Energy dependent morphology is a proof of electron origin in

G18.0-0.7. First detection of such morphology in HESS J1825-G18.0-0.7. First detection of such morphology in HESS J1825-137.137.

Particle dominated PWN are ideal VHE sources (de Jager & Particle dominated PWN are ideal VHE sources (de Jager & Venter 2005). This allow them to (a) have radiation maxima in IC Venter 2005). This allow them to (a) have radiation maxima in IC rather than synchrotron, and (b) maximal expansion sizes from rather than synchrotron, and (b) maximal expansion sizes from electron survival considerations.electron survival considerations.