the transient universe: ay 250 spring 2007 existing transient surveys: radio i: pulsars geoff bower

The Transient Universe: AY 250 Spring 2007

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

• Feb 1968: Nature paper summarizing discovery (Hewish & Bell etal 1968)


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


Alternatives to Pulsars

• Man-made interference

• Radar reflection off the Moon

• Television

• Reflections off nearby buildings

• LGM-1


Higher Time Resolution & Frequency Resolution

Regular pulses

Frequency dispersed pulses

Interstellar scintillation

Doppler variations and frequency stability


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


Pulsar in the Crab Nebula

Staelin & Reifenstein 1968Remnant of SN 1054


Optical Pulses from the Crab

Cocke et al 1969


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


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


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 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


Music of the Spheres

MSP: 1937+21

PSR 0329+54

PSR 08-33


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


Pulsar Searching

• Search in phase space of period, and dispersion measure– DM ~ n_e * L – Pulse phase ~ DM * lambda^2


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


Solution 2:Sideband Search

Ransom et al 2003P_obs > P_orb


Implementation of Sideband Search

47 Tuc J Simulated MSP


Improvement in Sensitivity From Sideband Search


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


Parkes Multi-Beam Survey


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


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


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 existing transient surveys: radio i: pulsars geoff bower

Documents

transient universe

orb slide

minutes slide

sideband search slide

frequency stability

existing transient surveys

scruff j bell slide

pulsars geoff bower