The Transient Universe: AY 250 Spring 2007
Existing Transient Surveys:Radio I:Pulsars
Geoff Bower
The Transient Universe: AY 250 Spring 2007
Pulsar Discovery
“a bit of scruff”-J Bell
The Transient Universe: AY 250 Spring 2007
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
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
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
Higher Time Resolution & Frequency Resolution
Regular pulses
Frequency dispersed pulses
Interstellar scintillation
Doppler variations and frequency stability
The Transient Universe: AY 250 Spring 2007
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
Pulsar in the Crab Nebula
Staelin & Reifenstein 1968Remnant of SN 1054
The Transient Universe: AY 250 Spring 2007
Optical Pulses from the Crab
Cocke et al 1969
The Transient Universe: AY 250 Spring 2007
The Transient Universe: AY 250 Spring 2007
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
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
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
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
Music of the Spheres
MSP: 1937+21
PSR 0329+54
PSR 08-33
The Transient Universe: AY 250 Spring 2007
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
Taylor & Weisberg 1982
The Transient Universe: AY 250 Spring 2007
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
But Binaries are the Most Interesting
and 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
Solution 2:Sideband Search
Ransom et al 2003P_obs > P_orb
The Transient Universe: AY 250 Spring 2007
Implementation of Sideband Search
47 Tuc J Simulated MSP
The Transient Universe: AY 250 Spring 2007
Improvement in Sensitivity From Sideband Search
The Transient Universe: AY 250 Spring 2007
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
Parkes Multi-Beam Survey
The Transient Universe: AY 250 Spring 2007
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
Pulsar Galactic Population
• Total number of galactic pulsars:– 30,000 detectable (~5% currently detected)– 155,000 +/- 6000 total– 1.4 +/- 0.2 per century
Smooth model Clumpy model
The Transient Universe: AY 250 Spring 2007
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
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