PULSAR ASTRONOMY Past, Present and Future Andrew Lyne
SUMMARY • Introduction • Pulsar Timing • Pulsars as Tools • Recent Advances • The Future
Formation Pulsars are created in Supernova-explosions: Burning Phase Collapse Supernova Explosion Angular momentum and magnetic flux are conserved
Current views suggest radius of 10-15 km Mass ~1.4 M Size and Structure 1011-14 g cm-3
Evolution of a pulsar (in1982) death-line Pulsars “die” after ~107 – 8 yr • In 1982 D.Backer et al. studied a strange polarized • steep spectrum source ..… • ….. and discovered the first Millisecond-Pulsar !!
Recycled pulsars – X-ray binaries • Mass transfer from companion spins up dead pulsar • Duration of this angular momentum transfer determines final spin period (as short as 1.5 ms) • Pulsar re-born as “recycled pulsar”
Pulsar Timing: Summary • Compare measured TOAs with a timing model • After coherent solution, random residuals • Rotational parameters • Positions • Proper motions • Binary parameters • Amazing precision e.g. Period of PSR B1937+21: P = 0.00155780649243270.0000000000000004 s or orbital eccentricity of PSR J1012+5307: e < 0.8 x 10-7 – roundest object in the universe!
Pulsar Timing: Binary pulsars • 5 Keplerian-parameters: Porb, apsini, e, , T0 • Allow calculation of companion minimum mass • Post-Keplerian parameters (GR terms) may be • measurable – allowing complete solution
Quantum mechanics predicts Mass =1.4 M Depends on Equation-of-State (EOS) Observations show values all consistent with 1.35±0.05 M Pulsar Timing: Masses of NS Thorsett & Chakrabarty ‘99
Pulsar Timing: Binary pulsars • Example for a binary system: PSR J1740-3052 Black Hole? Stairs et al. 2001 • 570-ms pulsar with companion in 230-d orbit • Eccentricity of 0.579 • Companion mass at least 11 M
PULSARS AS TOOLS Applications of pulsars: • Theories of gravity • Cosmology • Extra-solar planets • Supernova-Explosions • Interstellar and intercluster medium • Solid state physics under extreme conditions
Theories of Gravity: Gravitational Waves • Confirms General Relativity at level of 0.5% • Orbit shrinks every day by 1cm!
Theories of Gravity: Tests PSR B1913+16: Three PK parameters: in correct theory lines meet!
Cosmology Gravitational wave background from Big Bang: Pulsars=arms of huge gravitational wave detector Search for spatial patterns in timing residuals!
Cosmology Cosmic radiation from the from Big Bang:
First extra-solar planets First planetary system discovered around millisecond pulsar PSR B1257+12 by Wolszczan & Frail (1992)
Asymmetric Supernova-Explosions • There is much convincing evidence: • Most pulsars are solitary • High pulsar velocities (up to 1000 km/s) • Misalignment of pulsar and orbital spin • Pulsar/SNR offset: • Kick mechanism • unknown! • Hydrodynamical • Neutrino-driven • EM radiation-driven
Pulsar Proper Motions measured using MERLIN Nearly half of all pulsars will escape the Galaxy
The Galactic magnetic field • Field of Milky Way not well known at all! • Best information from pulsars: - Measure Faraday Rotation and DM • - Model galactic field
Glitches of young pulsars Solid state physics under extreme conditions: For /=10–8: R=-0.1mm!
Interior of Neutron Stars: Glitches Long-term spin-down and glitches superposed Vela pulsar • From relaxation process • we infer super-fluid interior • Large glitches arise from • Superfluid vortex pinning
RECENT ADVANCES • Discovery of Free Precession • Use of MSPs as gravitometers in GCs • The Parkes Multibeam Survey • Discovery of Magnetars and Magnetar-like radio pulsars • Observation in other wavebands
Free Precession of a Radio Pulsar !?! Stairs et al. 2000 PSR B1828–11: • Systematic timing residuals • Periods of 1000, 500 and 250 days • Pulse shape and torque correlated
Free Precession of a Radio Pulsar BUT: Free precession is not expected in case of pinned vortices in super-fluid interior!
Probing the core of 47 Tucanae • Using Parkes telescope • >20 MSPs detected • Recent discoveries using acceleration search • Most in binary systems • Shortest orbit of any radio pulsar, i.e. 96min • Accurate positions: • Proper Motions:
Probing the core of 47 Tucanae • Positive and negative dP/dt’s give acceleration • Gravitation model gives radial position • First detection of gas in a globular cluster !! • Freire et al (2001)
Old situation: New situation: The Parkes Multibeam Survey • Parkes 64m telescope • Frequency - 1400 MHz • 13 beams • International collaboration - Australia, UK, Italy, US • >600 new pulsars
OTHER WAVEBANDS • Optical – 5 pulsars • X-ray ~30 pulsars • -ray ~10
Magnetars, SGRs and AXPs XTE discovery of first Magnetar: • Soft Gamma-ray repeater (SGR) • Period ~ 5 – 10 s • High Pdot • Different emission process ? • Not seen in radio ! • Anomalous X-ray Pulsars (AXP) similar ?!
THE FUTURE • There is still much to be learned • Searches • Parkes (64m) is the smallest telescope to find a pulsar, and has found half the known population • FAST could find many with appropriate instrumentation • Timing • Long-term monitoring of young pulsars for glitches • Long-term monitoring of MSPS for astrometry, and studies of General Relativity and Gravitation • Technology • Coherent dedispersion over wide bandwidth is necessary for maximum timing precision • Interference mitigation strategies will become increasingly essential
Coherent Dedispersion • Normally use filterbanks • Resolution is limited by bandwidth of channels • Alternatively, use coherent dedispersion • Apply the inverse of the phase rotation applied by the ISM
Incoherentvs.CoherentDe-dispersion BUT – Coherent dedispersion requires much computing
COBRA – an on-line super-computer COBRA: Coherent On-line Baseband Receiver for Astronomy • Coherent Dedispersion of Pulsar Signals • Interference mitigation • Spectral Polarimetry • Methanol Multibeam spectrometer • Off-line pulsar search analysis
COBRA – Implementation • >100 MHz dual polarisation recording • 8-bit recording for high dynamic range • 400 Mbytes/sec input rate • 180 Pentium III processors in Beowulf cluster • Cheap, easy to programme, using Linux • Polarization comes free
ISM Receiver Coherent De-dispersion with COBRA 1 of 10 10-MHz COBRA modules Baseband Mixing PC cluster Sampling FFT Chirp FFT Folding Pulse Profile
Spectroscopy with COBRA • Main purpose is pulsar observations, but… • COBRA will also be used as spectroscopy backend • As only single FFT is required, computing power is sufficient for twice the bandwidth 1 COBRA module Baseband Mixing PC-cluster Sampling FFT Chirp FFT Folding Spectrum
THEFUTUREof pulsar astronomy and radio astronomy Lies in the software receiver