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Pulsars and Supernovae II 8. PULSAR BIRTH AND EVOLUTION -- BINARY AND MILLISECOND PULSARS association with supernova remnants evolution of binary systems recycled pulsars mass transfer and spin-up Hulse-Taylor pulsar and gravitational radiation globular cluster searches Close supernova remnants • There are ~50 supernova remnants (SNRs) within 5 kpc of us, from which we may hope to detect pulsars. • Statistically, we expect: – about 10 to be type 1a SNRs and therefore probably not associated with neutron stars. We know about two for sure: Tycho (Chandra) SN 1006 (Chandra) 2 8. Binary and millisecond pulsars Close supernova remnants G11.2-0.3 (Chandra) – about 10 -- 15 to have formed black holes – about 5 to have lost their neutron stars due to high proper motion. • There should therefore be about 15-20 associated with neutron stars. • We see that 10 have either pulsars or pulsar wind nebulae. 65 ms X-ray pulsar RCW 103 (Chandra) • A further ~10 have X-ray point sources at the centre, e.g. RCW 103. This one seems to be rotating with a period of 6.7 h. These ‘central compact objects’ are probably neutron stars. • About 10 are yet to be searched – the numbers seem to add up OK. 3 8. Binary and millisecond pulsars Close supernova remnants • The youngest, brightest, supernova remnant, Cassiopeia A, also has a clear point source at its centre in X-rays, but no pulsar. • The lack of a pulsar or pulsar wind nebula may indicate that the magnetic field is either too weak or (more likely) too strong to allow the particle acceleration to occur. Cas A (Chandra) 4 8. Binary and millisecond pulsars Cas A (Chandra) 5 8. Binary and millisecond pulsars Cas A (VLA) 6 8. Binary and millisecond pulsars Radio pulsars and supernova remnants • About 20 radio pulsars appear to be associated with supernova remnants, though only ~13 have supporting evidence that the association is real (rather than a chance alignment). • We expect these all to be young pulsars, and to appear close to the top of the P-Pdot diagram. • Radio pulsars have not been found in most of the ~300 known supernova remnants, due to a combination of statistics, surveying difficulties and the distances involved. 7 8. Binary and millisecond pulsars Evolution of binary systems • Not all pulsars are born in a simple isolated supernova explosion. Binary systems can show a range of evolutions as the two stars age, interact and form compact objects. • In the simplest scenario, a massive primary star evolves rapidly and undergoes a Type II supernova explosion. The mass-loss reduces the binding energy of the system. This, and the ‘rocket’ force on the resulting neutron star, can disrupt the binary. • We are left with a runaway secondary star and an isolated, high velocity pulsar. 8 8. Binary and millisecond pulsars Evolution of binary systems • If the binary system survives the collapse of the primary we get a binary pulsar, or a simple binary star/neutron star system. • As the secondary evolves it will, if sufficiently massive, swell to a red giant phase and overflow its Roche lobe, spilling material onto the (now spun-down) neutron star. • The accretion has two effects: – Orbital angular momentum is transferred to the neutron star, spinning it up, and forming a recycled pulsar. – An accretion disk is formed, and X- rays emitted as in-falling matter impacts the disk. 9 8. Binary and millisecond pulsars Mass transfer and spin-up 10 8. Binary and millisecond pulsars Recycled pulsars • On the P-Pdot diagram, recycled pulsars are clearly associated with binary systems (circles/ellipses): • The shortest period recycled pulsars have periods of a few milliseconds, and nearly circular orbits (circles on the diagram). • Mildly recycled pulsars have had less time to spin-up and to circularise their orbits (shown as ellipses on the diagram). • about 80% are in binary Lorimer 2001 systems. 11 8. Binary and millisecond pulsars Recycled pulsars Lorimer 2008 12 8. Binary and millisecond pulsars Evolution of binary systems • The fate of this X-ray binary system depends on the mass of the companion star • If the system is a low-mass X-ray binary (LMXB), the mass transfer continues for a greater length of time, and the recycled pulsar is spun-up to a very short (~ms) rotation period. • Eventually, the companion sheds its outer envelope and becomes a white dwarf. • Orbits are generally highly circular (eccentricity ≪ 0.01). 13 8. Binary and millisecond pulsars Evolution of binary systems • You can sometimes see the white-dwarf companion at the location of the radio pulsar, e.g. J0218+4232 (~10 known) white dwarf ~8000 K ~0.2 solar masses J0218+4232 (Bassa et al 2003) 14 8. Binary and millisecond pulsars Evolution of binary systems • If the system is a high-mass X-ray binary (HMXB), the companion will quickly form a supernova. • If the binary system survives, we have a double neutron star binary system. Eccentricity Is generally large. • If the binary system is disrupted (as seems to be common) we have two free pulsars -- one young and the other mildly recycled. 15 8. Binary and millisecond pulsars Hulse-Taylor pulsar and gravitational radiation • This is a famous double neutron star system PSR B1913+16. Such systems can be quite relativistic, and need post-keplerian orbital parameters to describe the orbital evolution. • Keplerian: – Orbital period – Projected semi-major axis – Orbital eccentricity – Longitude of periastron – Epoch of periastron passage • Can’t determine individual masses or orbital inclination. • Post-keplerian: – Advance of periastron – Gravitational redshift – Orbital decay rate • These allow the determination of orbital inclination and individual masses. 16 8. Binary and millisecond pulsars Hulse-Taylor pulsar and gravitational radiation • The ‘advance of periastron’ parameter was the first clear evidence of gravitational radiation – GR predicts this to be particularly sensitive to the effects of radiation reaction. Weisberg & Huang 2016 17 8. Binary and millisecond pulsars Globular cluster searches • Globular clusters are a rich hunting ground for recycled pulsars, due to the high probability of interaction. Currently 138, in 25 globular clusters. Terzan 5 (B. Saxton (NRAO/AUI/NSF); GBO/AUI/NSF; NASA/ESA Hubble, F. Ferraro) Scott Ransom 18 8. Binary and millisecond pulsars Globular cluster searches • There are 23 millisecond radio pulsars in 47 Tucanae: Michael Kramer 19 8. Binary and millisecond pulsars.
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