R. N. ManchesterAustralia Telescope National Facility, CSIRO, Sydney

Australia

Pulsars – a short introduction

Parkes pulsar surveys – the double pulsar

Pulsars as probes the interstellar medium

Pulsars with the Fermi gamma-ray telescope

Detecting gravitational waves with pulsars

Pulsars – Fascinating Objects and Marvellous Probes

Spin-Powered Pulsars: A Census

• Number of known pulsars: ~1820

• Number of millisecond pulsars: 181

• Number of binary pulsars: 139

• Number of AXPs: 13

• Number of pulsars in globular clusters: 107*

• Number of extragalactic pulsars: 20

Data from ATNF Pulsar Catalogue, V1.33 (www.atnf.csiro.au/research/pulsar/psrcat; Manchester et al. 2005)

* Total known: 137 in 25 clusters (Paulo Freire’s web page)

Pulsar Recycling - Millisecond Pulsars

Millisecond pulsars (MSPs) are very old (~109 years).

Most of them are members of a binary system - in orbit with another star

They have been recycled by accretion from an evolving binary companion.

This accretion spins up the neutron star to millisecond periods.

Neutron stars are tiny (about 25 km across) but have a mass of about 1.4 times that of the Sun

They are incredibly dense and have gravity 1012 times as strong as that of the Earth

Because of this large mass and small radius, their spin rates - and hence pulsar periods - are incredibly stable

e.g., PSR J0437-4715 had a period of :

5.757451831072007 0.000000000000008 ms

Although pulsar periods are very stable, they are not constant. Pulsars lose energy and slow down

Typical slowdown rates are less than a microsecond per year

Pulsars as Clocks

P vs P.

Galactic disk pulsars

ATNF Pulsar Catalogue(www.atnf.csiro.au/research/pulsar/psrcat)

• Most pulsars have P ~ 10-15

• MSPs have P smaller by about 5 orders of magnitude

• Most MSPs are binary

• Only a few percent of normal pulsars are binary

• P/(2P) is an indicator of pulsar age

• Most young pulsars are associated with supernova remnants

..

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The Parkes radio telescope has found more than twice as many pulsars as the rest of the world’s telescopes put together.

Multibeam receiver - 13 beams at 1.4 GHz - very efficient for pulsar surveys

Several independent surveys with different optimisations

More than 850 pulsars discovered with the multibeam system since 1997

Excellent database for studies of pulsar Galactic distribution and evolution

The Parkes Multibeam Pulsar Surveys

(Manchester et al. 2001)

The Parkes Multibeam Pulsar Surveys: Galactic Distribution

Parkes Multibeam Surveys: P vs P

.J1119-6127

• New sample of young, high-B, long-period pulsars

• Large increase in sample of mildly recycled binary pulsars

• Three new double-neutron-star systems and the first-known double pulsar!

J0737-3039

The first double pulsar!

Discovered at Parkes in 2003

One of top ten science break-throughs of 2004 - Science

PA = 22 ms, PB = 2.7 s

Orbital period 2.4 hours!

Periastron advance 16.9 deg/yr!(Burgay et al., 2003; Lyne et al. 2004)

Highly relativistic binary system!

PSR J0730-3039A/B

PSR J0737-3039A/B Post-Keplerian Effects

R: Mass ratio

: periastron advance

: gravitational redshift

r & s: Shapiro delay

Pb: orbit decay

(Kramer et al. 2006)

.

.

GR is OK! Consistent at the

0.05% level!

Non-radiative test: distinct from PSR B1913+16

PSR J0737-3039A Eclipses• Pulses from A eclipsed for ~30 sec each orbit• Eclipse by B magnetosphere – orbit seen nearly edge on

• High-resolution observations show modulation of eclipse at rotation period of B pulsar!

(McLaughlin et al., 2004)

PSR J0737-303A Eclipse Model

• Synchrotron absorption by high-density plasma in the magnetospheric closed field-line region

• Model fitted to observed eclipses to determine properties of eclipsing region

(Lyutikov & Thompson 2005)

• Geodetic precession B spin axis with 75-year period expected from GR

• Changing orientation of spin axis changes pattern of eclipse modulation

• Lyutikov & Thompson eclipse model fitted to four-year data span

• Evidence for change in longitude of spin axis – consistent with GR prediction

PSR J0737-3039A Eclipses: Evidence for Geodetic Precession of

PSR J0737-3039B

(Breton et al. 2008)

Pulsars as Probes Pulsars are:

• Essentially point sources• Broad-band pulsed emitters• Highly polarised• Distributed through Galaxy at approximately known distances

These properties make them near ideal probes of the interstellar medium (ISM)

For example, scattering by small-scale irregularities in the ISM results in interstellar scintillation of pulsars

Interference pattern is function of frequency and, because of motion of the pulsar and the Earth, also of time – “dynamic spectrum”

Two-dimensional Fourier transform of dynamic spectrum gives a “secondary spectrum”

Can investigate ISM on scales as small as 0.1 A.U. (1010 m)

(Stinebring, 2006)

Faraday rotation of the plane of polarisation of pulsar emission is easily observed

The ratio of the Rotation Measure to the Dispersion Measure gives a direct measure of the mean line-of-sight magnetic field strength (weighted by the local electron density) :

Pulsars are highly polarised – close to 100% linear polarisation in some cases

Probing the Galactic Magnetic Field with Pulsars

(Han et al. 2009, in prep.)

Pulsars are spread through the Galaxy at approximately known distances, making possible three-dimensional tomography of the Galactic magnetic field

Rotation measures now available for nearly 400 pulsars

(Pulse truncated at 20% of peak)

Linear

Circular

PSR J0437-4715 1433 MHz

EGRET Sky survey: 1991-1995

Vela Geminga

Crab

The Gamma-ray Sky

Fermi Gamma Ray Space Telescope

In clean room before launch

Launched June 11, 2008

LAT

Fermi – Three-month image

Fermi – Vela Pulsar

(Abdo et al. 2009)

Radio pulse

Fermi – CTA1 Pulsar

(Abdo et al. 2008)

First gamma-ray pulsar found in a blind search!

EGRET pulsarsEGRET pulsars

young pulsars discovered using radio ephemerisyoung pulsars discovered using radio ephemeris

pulsars discovered in blind searchpulsars discovered in blind search

25 gamma-ray and radio pulsars (including 7 ms psrs)25 gamma-ray and radio pulsars (including 7 ms psrs)

13 gamma-ray only pulsars13 gamma-ray only pulsars

High-confidence detections through 10/31/2008

millisecond pulsars discovered using radio ephemerismillisecond pulsars discovered using radio ephemeris(Credit: P. Michelson)

Pulses at 1/10th real rate

Detection of Gravitational Waves• Huge efforts over more than four decades to detect gravitational waves

• Initial efforts used bar detectors pioneered by Weber

• More recent efforts use laser interferometer systems, e.g., LIGO, VIRGO, LISA

• Two sites in USA• Perpendicular 4-km arms• Spectral range 10 – 500 Hz• Initial phase now operating• Advanced LIGO ~ 2011

LISALIGO• Orbits Sun, 20o behind the Earth• Three spacecraft in triangle• Arm length 5 million km• Spectral range 10-4 – 10-1 Hz• Planned launch ~2018

A Pulsar Timing Array• With observations of many pulsars widely distributed on the sky can in principle detect a stochastic gravitational wave background

• Gravitational waves passing over the pulsars are uncorrelated

• Gravitational waves passing over Earth produce a correlated signal in the TOA residuals for all pulsars

• Requires observations of ~20 MSPs over 5 – 10 years; could give the first direct detection of gravitational waves!

• A timing array can detect instabilities in terrestrial time standards – establish a pulsar timescale

• Can improve knowledge of Solar system properties, e.g. masses and orbits of outer planets and asteroids

Idea first discussed by Hellings & Downs (1983), Romani (1989) and Foster & Backer (1990)

Clock errors

All pulsars have the same TOA variations: monopole signature

Solar-System ephemeris errors

Dipole signature

Gravitational waves

Quadrupole signature

Can separate these effects provided there is a sufficient number of widely distributed pulsars

The Parkes Pulsar Timing Array ProjectCollaborators:

Australia Telescope National Facility, CSIRO, SydneyDick Manchester, George Hobbs, David Champion, John Sarkissian, John Reynolds, Mike Kesteven, Warwick Wilson, Grant Hampson, Andrew Brown, Jonathan Khoo, (Russell Edwards, David Smith)

Swinburne University of Technology, MelbourneMatthew Bailes, Willem van Straten, Ramesh Bhat, Sarah Burke, Andrew Jameson

University of Texas, BrownsvilleRick Jenet

University of California, San DiegoBill Coles

West Virginia UniversityJoris Verbiest

Franklin & Marshall College, Lancaster PAAndrea Lommen

University of Sydney, SydneyDaniel Yardley

National Observatories of China, BeijingZhonglue Wen

Peking University, BeijingKejia Lee

Southwest University, ChongqingXiaopeng You

Curtin University, PerthAidan Hotan

Sky Distribution of Millisecond PulsarsP < 20 ms and not in globular clusters

Recent Results for PSR J0437-4715

Rms timing residual 56 ns!!

Current PPTA Results

• Timing for 20 MSPs

• Four pulsars with timing residuals less than 200 ns and eleven less than 1 s

These results are approaching the level needed to detect gravitational waves in 5 - 10 years!

Still more work to be done to reduce systematic errors!

Name Period DM Orbital period

Band Rms Residual

(ms) (cm-3 pc) (d) (s)

J0437-4715 5.757 2.65 5.74 10cm 0.08

J0613-0200 3.062 38.78 1.2 20cm 0.54

J0711-6830 5.491 18.41 - 20cm 1.27

J1022+1001 16.453 10.25 7.81 10cm 1.8

J1024-0719 5.162 6.49 - 20cm 1.06

J1045-4509 7.474 58.15 4.08 20cm 1.59

J1600-3053 3.598 52.19 14.34 20cm 0.28

J1603-7202 14.842 38.05 6.31 20cm 0.96

J1643-1224 4.622 62.41 147.02 20cm 0.94

J1713+0747 4.57 15.99 67.83 10cm 0.2

J1730-2304 8.123 9.61 - 20cm 1.62

J1732-5049 5.313 56.84 5.26 20cm 2.89

J1744-1134 4.075 3.14 - 10cm 0.41

J1824-2452 3.054 119.86 - 10cm 1.95

J1857+0943 5.362 13.31 12.33 20cm 0.45

J1909-3744 2.947 10.39 1.53 10cm 0.11

J1939+2134 1.558 71.04 - 10cm 0.17

J2124-3358 4.931 4.62 - 20cm 2.86

J2129-5721 3.726 31.85 6.63 20cm 1.49

J2145-0750 16.052 9 6.84 20cm 0.36

Future ProspectsSingle source detection

Stochastic GW BackgroundPPTA

SKA

Range of predicted amplitudes(Jaffe & Backer 2003; Wyithe & Loeb 2003)

5 years, 100 ns

Difficult to get sufficient observations with PPTA alone - international collaborations important!

Predicted merger rates for 5 x 108 M binaries (Wen & Jenet 2008)

PPTA can’t detect individual binary systems - but SKA will!

The Gravitational Wave Spectrum