Pulsars are rapidly rotating neutron stars from which we observe strong radio emissions. Observed changes in pulsar rotation frequency can suggest the presence of a binary companion. Pulsars with high rotation frequencies are almost always found in binaries. This is well explained by the theory of pulsar spin-up: matter is accreted to the neutron star from a main sequence companion. This increases the neutron star’s rotation speed due to the conservation of angular momentum, a process called recycling. If the binary is a double neutron star system, spin periods will be higher due to incomplete recycling. Double neutron star systems provide some of the most stringent tests of gravity, however their population is small and the key indicators for their evolution are poorly constrained. This work presents and discusses the results from observations of five recycled radio pulsar signals.
PSR J1829+2456 is a member of a double neutron star system. Observations over three consecutive years have allowed measurement of the system’s proper motion and component masses, found to be1.306±0.007M and 1.299 ± 0.007M for the neutron star and its companion, respectively. The proper motion implies a low-to-moderate space velocity of∼50 km s−1which, in tandem with the measured masses and mild orbital eccentricity, suggests the system is the result of a low-kick, symmetric ultra-stripped iron core-collapse supernova.
PSRs J1851+0010, J1853+0008, J1936+1805 and J1936+2142 were discovered by the Pulsar Arecibo L-band Feed Array (PALFA) survey collaboration. The former two are believed to be members of double neutron star systems. Component masses for both systems have been measured with the companion of PSR J1851+0010 being1.15 ± 0.04M: possibly the lowest mass neutron star discovered to-date. These systems are thought to have evolved in a similar way to PSR J1829+2456. Time dependent pulse width analysis is consistent with this hypothesis. PSR J1936+1805 is an isolated pulsar with a rotation frequency of≈17rotations per second. This may be a disrupted binary: a pulsar that was once part of a binary system that did not survive long-term. PSR J1936+2142 is believed to be a neutron star-white dwarf binary with an orbital period of 0.757days. The observed pulse frequency decay implies this pulsar is old, with a characteristic age of eleven billion years. Orbital parameters suggest that this system is an intermediate mass binary pulsar
