Radio Pulsar Phenomenology: What can we learn from pulsar profiles?

Radio Pulsar Phenomenology:What can we learn frompulsar profiles?Simon Johnston (ATNF, CSIRO)Aris Karastergiou (Oxford, UK)

Outline• Brief tour through the basics• P-Pdot diagram• The Rotating Vector Model– Obtaining pulsar geometry• What we’ve learned from integrated profiles– Beam models• Thoughts

Basic Observables and Derivables. I.Measurespin period, P, and its derivatives, dP/dt etcDeriveSpin down energy: Edot = 4π 2 I Pdot/P 3Magnetic Field: B = 3.2×10 19 √(P Pdot) Braking index: n = νν/ν 2Characteristic Age: τ c = Pdot / (n-1)PLight cylinder radius: R lc = 4.77×10 4 P

Basic Observables and Derivables. II.MeasureDM, RM, Tscatt, HI absorptionDeriveInterstellar medium densityInterstellar medium magnetic fieldInterstellar medium turbulencePulsar distances Global picture of Galaxy structure

Basic Observables and Derivables. II.MeasureDM, RM, TscattJohnston et al. 2005Loehmer et al. 2004Image: Reiner Beck

Basic Observables and Derivables. III.MeasurePulse arrival times, glitch parameters,timing noise, binary parametersDeriveTests of general relativityDetection of gravitational wavesPulsar distancesNS interior density profile and structureEquation of state

Kramer et al. 2006Image: NASAVerbiest et al. 2010

Basic Observables and Derivables. IV.Single pulses – an area rich in phenomenologyKarastergiou et al. 2001Weltevrede et al. 2007van Leeuwen et al. 2003DeriveEmission physics, emission modelsHankins & Eilek 2007

Basic Observables and Derivables. V.MeasureIntegrated Pulsar ProfilesDeriveGeometry, emission heights, beamstructure, emission physics, beam models

Assumptions aboutradio emission• Emission from open fieldlines above polar cap• Dipolar magnetic field• Emission from near surface• Must be coherent emission(unlike at high energies)Could argue about allthese assumptions!

Pulsar geometry and therotating vector modelImportant angles are:α – angle between therotation and magnetic axisβ – closest approach of lineof sight to magnetic axisρ – cone opening angleThe RVM uses the PA swing to derive the geometry

The Rotating Vector Model (RVM) for polarization 150 o Longitude

The Rotating Vector Model (RVM) for polarization Longitude

The Rotating Vector Model (RVM) for polarization Longitude

The Rotating Vector Model (RVM) for polarization Longitude

The Rotating Vector Model (RVM) for polarization Longitude

The Rotating Vector Model (RVM) for polarization 90 o Longitude

The Rotating Vector Model (RVM) for polarization Longitude

The Rotating Vector Model (RVM) for polarization Longitude

The Rotating Vector Model (RVM) for polarization Longitude

The Rotating Vector Model (RVM) for polarization Longitude

The Rotating Vector Model (RVM) for polarization Longitude

The Rotating Vector Model (RVM) for polarization 30 o Longitude

α = 30, β = -1.7α = 86, β = -3.2RVM fit inalpha-betaspace

α = 30, β = -1.7α = 86, β = -3.2Ambiguity due to restrictedlongitude range!!

RVM is a useful tooland geometry iscrucial for testingmodels of γ-rayemission (and radioemission). In practice,hard to constrain.This PA swing is “forbidden” by the RVM, and is likelythe result of magnetospheric or propagation effects.

Mapping the magnetosphere• We can use the radio observations to make a3D map of the emission zones– Need geometry– Need a method of computing altitudes– Need a large sample of pulsars• BUT– Geometry often uncertain– Conflicting results from altitude derivations• Models of the beam

Beam modelsof Rankindeveloped in aseries ofpapers since1983.In a nutshell: Two different types of emission, fromthe “core” and from “cones”. Emission heights aretypically 300 km at 1 GHz. Circular polarization signchange in the core. Elliptical beams.

Beam modelof Lyne &ManchesterIn a nutshell: No distinction between “core” and“cone” emission. Patchy beams with randomemission locations. Circular beams.

Emission heightversus longitudefrom Gangadhara& GuptaIn a nutshell: Emission far from the centre occurs athigher heights than emission from the centre at agiven observing frequency.

Young pulsarstudy ofJohnston &WeisbergIn a nutshell: Highly polarized, double component(simple) pulsars with high emission heights. Somehave large widths.

Linear polarization fraction versus EdotWeltevrede &Johnston showthat Edot is acrucialparameter!Abrupt transition betweenfrom low to high polarizationstates around Edot of 10 34.5 .No orthogonal mode jumps. Onemode dominates but this is split50:50 between parallel andorthogonal modes!!

Polarization and the P-Pdot diagramWeltevrede & Johnston 2008Harding et al. 2002Links with high energy slot-gap models??

Pulse width versus EdotOrthogonal rotatorsHigh Edot, widebeam single poleLow Edotaligned rotatorsWeltevrede &Johnston studyof interpulsepulsars.In a nutshell: Random orientation of B-Ω axis atbirth, becoming aligned over time.

Orthogonal RotatorsWeltevrede & Wright 2009Kramer & Johnston 2008Beam mapping of B0906-49 (left) and B1055-52(above) following RVM fits. Emission heights similarabove both poles. Evidence for emission from theclosed field lines (see also Keith et al. 2010).

Beam model ofKarastergiou &JohnstonHigh EdotLow EdotIn a nutshell: High single emission height for highEdot pulsars, multiple heights for low Edot pulsars.Explains high beaming fraction of high Edot pulsars.

Summary• The integrated profiles give information on– Geometry, emission heights, the static magnetosphere• Beam models and observations tell us– Clear evidence of conal emission, beam is patchy, emission heightvaries across polar cap• High Edot (non MSP) pulsars– Highly polarized, from high emission heights, implying a highbeaming fraction– Geometry poorly constrained in most cases.– Distances are poorly known (until the SKA?)– Often (always?) γ-ray emitters• MSPs– Polarization low– Better handle on (low DM) distances

Questions• What is the radio/gamma beaming fraction?– For young, high Edot pulsars?– For MSPs?• Is there a link between the radio and the γ-ray apartfrom geometric considerations?– Locations of the emission regions?– Why so many γ-ray MSPs?• What do the orthogonal rotators tell us?– Very well determined geometry– “known” radio emission regions