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Existing Transient Surveys: Radio I: Pulsars

Existing Transient Surveys: Radio I: Pulsars. Geoff Bower. Pulsar Discovery. “a bit of scruff” -J Bell. PSR Discovery Timescale. July 1967: MRAO in operation Aug 1967: First PSR signals detected Nov 1967: Systematic observations of PSR 1919+22 Dec 1967: Three more PSRs known

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Existing Transient Surveys: Radio I: Pulsars

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  1. Existing Transient Surveys:Radio I:Pulsars Geoff Bower The Transient Universe: AY 250 Spring 2007

  2. Pulsar Discovery “a bit of scruff” -J Bell The Transient Universe: AY 250 Spring 2007

  3. PSR Discovery Timescale • July 1967: MRAO in operation • Aug 1967: First PSR signals detected • Nov 1967: Systematic observations of PSR 1919+22 • Dec 1967: Three more PSRs known • Feb 1968: Nature paper summarizing discovery (Hewish & Bell etal 1968) The Transient Universe: AY 250 Spring 2007

  4. MRAO • Array of 2048 dipoles operating at 81.5 MHz with 1 MHz bandwidth • Built for interplanetary scintillation of quasar signals • Required high time resolution (0.1 second) • Hewish designed and Bell with other students build telescope over a couple of years The Transient Universe: AY 250 Spring 2007

  5. Alternatives to Pulsars • Man-made interference • Radar reflection off the Moon • Television • Reflections off nearby buildings • LGM-1 The Transient Universe: AY 250 Spring 2007

  6. Higher Time Resolution & Frequency Resolution Frequency dispersed pulses Doppler variations and frequency stability Regular pulses Interstellar scintillation The Transient Universe: AY 250 Spring 2007

  7. Progress of Understanding • Immediate association with compact objects • Frequency sweep 5 MHz/s • Instantaneous bandwidth 80 kHz •  t<0.016 s  r<5000 km • White dwarfs or neutron stars • Pulsation? (Hewish model) • Normal modes • 8 s for WD • 1 s for NS density The Transient Universe: AY 250 Spring 2007

  8. Pulsar in the Crab Nebula Remnant of SN 1054 Staelin & Reifenstein 1968 The Transient Universe: AY 250 Spring 2007

  9. Optical Pulses from the Crab Cocke et al 1969 The Transient Universe: AY 250 Spring 2007

  10. The Transient Universe: AY 250 Spring 2007

  11. Very Rapid Theoretical Progress • Basic model converged on within months • Dozens of pulsars discovered • Papers on • Interstellar scintillation • High energy emission • Cosmic rays • Synchrotron radiation • Electrodynamics • Optical and X-ray pulsars • Polarization The Transient Universe: AY 250 Spring 2007

  12. Discovery of the Millisecond Pulsar • Backer, Kulkarni, Heiles, Davis, Goss 1982 • 1.5 msec period • Search driven by IPS & steep spectrum • Missed by earlier searches with less time resolution • Computational requirements grow as P_min^-2 The Transient Universe: AY 250 Spring 2007

  13. Significance of the MSP • Rotation frequency ~642 Hz close to breakup for 1 M_sun neutron star • At 2000 Hz and 10 km radius, centrifugal and gravitational forces in equilibrium • Extreme accuracy in timing possible • 10^-15 s/s The Transient Universe: AY 250 Spring 2007

  14. The Pulsar Population • Spin down • E_dot ~ B^2 P^-4 • E ~ P^-2 • B^2 ~ P*P_dot • Pulsars in SNR • Normal pulsars • Death line • Spin up of MSP pulsars • Diversity of B-field The Transient Universe: AY 250 Spring 2007

  15. Music of the Spheres PSR 0329+54 PSR 08-33 MSP: 1937+21 The Transient Universe: AY 250 Spring 2007

  16. Binary Pulsars • PSR 1913+16 • Pulsar – NS binary • Precision timing gives • Orbital elements • Constraints on masses • NS masses ~1.4 M_sun as predicted by equation of state • GR induced shift in period ~10^-12 s/s due to gravitational radiation The Transient Universe: AY 250 Spring 2007 Taylor & Weisberg 1982

  17. Pulsar Searching • Search in phase space of period, and dispersion measure • DM ~ n_e * L • Pulse phase ~ DM * lambda^2 The Transient Universe: AY 250 Spring 2007

  18. But Binaries are the Most Interestingand Short Period Binaries are the Most Interesting of Those • For pulsar searching, pulse period changes within a fraction of an orbit • Solution 1: Add period derivative search (or acceleration) • This is sensitive to P_orb >> P_observe • So, sensitivity is limited to detect short orbital periods: can be < 10 minutes The Transient Universe: AY 250 Spring 2007

  19. Solution 2:Sideband Search P_obs > P_orb Ransom et al 2003 The Transient Universe: AY 250 Spring 2007

  20. Implementation of Sideband Search Simulated MSP 47 Tuc J The Transient Universe: AY 250 Spring 2007

  21. Improvement in Sensitivity From Sideband Search The Transient Universe: AY 250 Spring 2007

  22. The Payoff for a New Technique • 21 MSPs in Globular Cluster Ter 5 • 25% increase over total number in GCs from previous 35 years • 13 binaries including two eclipsing and two highly eccentric systems • NS masses in range 1.7 – 1.96 M_sun • Due to collisions in the GC • Probe of interactions, mass segregation Ransom et al 2005 The Transient Universe: AY 250 Spring 2007

  23. Parkes Multi-Beam Survey The Transient Universe: AY 250 Spring 2007

  24. Parkes MBS • The most successful PSR survey ever • 742 PSRs discovered • Doubling previous number known • A number of exotic objects found • RRATs • Numerous binaries • Double pulsar system The Transient Universe: AY 250 Spring 2007

  25. Pulsar Galactic Population Smooth model Clumpy model • Total number of galactic pulsars: • 30,000 detectable (~5% currently detected) • 155,000 +/- 6000 total • 1.4 +/- 0.2 per century The Transient Universe: AY 250 Spring 2007

  26. Innovation and Pulsar Science • Instrumental • Low frequency instrumentation • High time resolution IPS telescope • Msec time resolution backend • Parkes Multibeam for large scale survey • Technical • Search techniques • New binary search technique • More to do • Higher frequencies, complete surveys, greater sensitivity, giant pulses, exotic objects The Transient Universe: AY 250 Spring 2007

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