Pulsar Wind Nebulae with LOFAR

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Pulsar Wind Nebulae with

LOFARJason Hessels

(ASTRON/UvA)

Astrophysics with E-LOFAR - Hamburg - Sept. 16th -19th, 2008

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OutlineObserving Pulsar Wind Nebulae (PWNe)

with LOFAR

General theoretical model of PWNe Observational properties of PWNe Observing PWNe with LOFAR


Pulsar Wind Nebulae (PWNe):

< 10% of “spin-down” energy converted into pulsations

Majority is released as a pulsar wind

The wind continuously injects high-energy electrons/positrons and magnetic field at the centre of an expanding supernova remnant producing a synchrotron nebula

In general, PWNe are found around the youngest and/or most energetic pulsars,

Wind persists beyond point where nebula is visible

Not just young pulsars: also high Edot, or strong wind confinement (high-velocity pulsars)

•~ 50 PWNe known

a.k.a. “Plerions”

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Chandra time-lapse view of Crab PWN

From Gaensler & Slane (2006)

Schematic PWN

PWN: Synchrotron-emitting bubble of energetic particles at the center of an expanding supernova remnant

Wind is not isotropic: equatorial and polar outflows

Crab is in many ways the prototype

Also bow-shock nebulae (high-velocity pulsars) and wind shocks in compact binaries

(young pulsar case)

Observational CharacteristicsMost PWNe only observed at cm radio and 1-10 keV X-rays

Decreasing size of nebula going from radio to X-rays

General radio properties:-- radio-emitting e-/e+ have very - long synchrotron lifetimes- amorphous (not shell-like or torii) - filaments and other structures- high (>10%) fractional linear - polarization- flat, non-thermal, power-law - spectrum (alpha = 0.0-0.3) - need for spectral break between - radio and X-rays

Crab Nebula From Gaensler & Slane (2006)

Astrophysics of PWNe

Pulsar birth properties (link to progenitor properties?)

Understanding the P-Pdot diagram (i.e. pulsar energetics and magnetic fields)

Relativistic flows/shocks (can resolve nebula)

Particle acceleration and interaction with ISM

Strong link with Galactic population of rare GeV and TeV sources

PWN with LOFAR

Detect SNR shells around known PWNe

Roughly half of the ~50 known PWNe are “naked”

e.g. the elusive Crab SNR shell (crab supernova blast wave hasn’t interacted with enough surrounding gas yet?)

Provide information on the composition and density profile of the material that the nebula is expanding into (relation between environment and morphology)

-



G11.2-0.3 Roberts et al. 2002

PWN with LOFARWhere does the radio spectrum turn over?

Flat spectrum in the radio with one or several spectral breaks necessary to connect with the X-rays

At what low freq does this turn over? (does emission become self-absorbed?)

PWNe will be dim, LOFAR’s huge collecting area will be critical

LOFAR

PWN with LOFARMorphology and Extent

Radio-emitting electrons have very long synchrotron lifetimes, trace energetic history of the pulsar

Radio filaments and other features marking regions of instability

LOFAR (long baselines incl.) will have similar (arcsecond) resolution to Chandra

Compare X-ray/radio morph.

Larger/smaller extent at low freq.?

G0.9+0.1 Dubner et al. 2008G11.2-0.3 Roberts et al. 2003

Soft X-ray Hard X-ray Radio

PWN with LOFARSpatially Resolved Spectroscopy and Polarimetry

Electron cooling as one moves away from pulsar

Spectral steepening observed in X-rays (also in radio?)

Polarimetry (not yet possible in X-rays) to trace magnetic structure far out in the nebula

Relate to pulsar geometry and proper motion

Vela - Dodson et al. 2003

Direction of proper motion and spin axis

PWN with LOFAR

Pulsar Winds in Binary Systems

Pulsar wind can be strongly confined near the pulsar

Probe the wind at very small distance from the pulsar

Double pulsar PSR J0737-3039 (within light cylinder)

Black-widow pulsars (PSR B1957+20)

Be-star companions (PSR B1259-63, LSI +61o 303?)LSI +61o 303

Dhawan et al. 2006

The TeV Sky in 2008

figures courtesy Jim Hinton

VERITAS (“northern HESS”) also coming online

Target Galactic TeV sources

PWN with LOFAR



Summary

PWN observations with LOFAR

Find SNR shells around “naked” PWNe

Map low-frequency spectrum and cut-off

Morphology and extent

Spatially resolved spectroscopy and polarimetry

Find new PWNe in binary systems or associated

with Galactic TeV sources


Pulsar Wind Nebulae with LOFAR

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