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Pulsar Wind Nebulae with LOFAR Jason Hessels (ASTRON/UvA) Astrophysics with E-LOFAR - Hamburg - Sept. 16 th -19 th, 2008.

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Presentation on theme: "Pulsar Wind Nebulae with LOFAR Jason Hessels (ASTRON/UvA) Astrophysics with E-LOFAR - Hamburg - Sept. 16 th -19 th, 2008."— Presentation transcript:

1 Pulsar Wind Nebulae with LOFAR Jason Hessels (ASTRON/UvA) Astrophysics with E-LOFAR - Hamburg - Sept. 16 th -19 th, 2008

2 Outline Observing 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. 16 th -19 th, 2008

3 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” Chandra time-lapse view of Crab PWN

4 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)

5 Observational Characteristics Most 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 = ) - need for spectral break between - radio and X-rays Crab Nebula From Gaensler & Slane (2006)

6 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

7 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) - G Roberts et al. 2002

8 PWN with LOFAR Where 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

9 PWN with LOFAR Morphology 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.? G Dubner et al G Roberts et al Soft X-ray Hard X-ray Radio

10 PWN with LOFAR Spatially 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 Direction of proper motion and spin axis

11 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 J (within light cylinder) Black-widow pulsars (PSR B ) Be-star companions (PSR B , LSI +61 o 303?) LSI +61 o 303 Dhawan et al. 2006

12 The TeV Sky in 2008 figures courtesy Jim Hinton VERITAS (“northern HESS”) also coming online Target Galactic TeV sources PWN with LOFAR

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


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