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