Normal Pulsars Research Articles

The Parkes Southern Pulsar Survey -- II. Final results and population analysis

ABSTRA C T A survey of the entire southern sky for millisecond and low-luminosity pulsars using the ATNF Parkes radio telescope has now been completed. The survey detected 298 pulsars, of which 101 were previously unknown. The new pulsars include 17 millisecond pulsars. This is the largest sample of both normal and millisecond pulsars detected in any survey. Combining our sample with other recent surveys in the Northern Hemisphere, we present a statistical study of the populations of both normal and millisecond pulsars. We find that the improved statistics allow us to estimate the number and birth-rate of both types of pulsar down to a 400-MHz luminosity limit of 1 mJy kpc 2 . The local surface densities of potentially observable normal pulsars and millisecond pulsars are both about 30 kpc π2 , corresponding to ,30 000 potentially observable pulsars of each type in the Galaxy. Once beaming effects are taken into consideration we estimate that the active population of normal pulsars is ,160 000. Although there is evidence for flattening of the luminosity function of normal pulsars, this is not evident for millisecond pulsars which probably have a substantial population with luminosities below 1 mJy kpc 2 . After correcting for beaming effects, we estimate that a normal pulsar is born with a luminosity greater than 1 mJy kpc 2 between once every 60 and 330 yr in the Galaxy. The birth-rate of millisecond pulsars is at least 3 〈 10 π6 yr π1 above the same luminosity limit. Modelling the observed transverse speeds of millisecond pulsars using a dynamical simulation, we find their mean birth velocity to be 130 6 30 km s π1 , significantly lower than that of the normal pulsars.

Timing models for the long orbital period binary pulsar PSR B1259-63

The pulsar PSR B1259–63 is in a highly eccentric 3.4-yr orbit with the Be star SS 2883. Timing observations of this pulsar, made over a 7-yr period using the Parkes 64-m radio telescope, cover two periastron passages, in 1990 August and 1994 January. The timing data cannot be fitted by the normal pulsar and Keplerian binary parameters. A timing solution including a (non-precessing) Keplerian orbit and timing noise (represented as a polynomial of fifth order in time) provides a satisfactory fit to the data. However, because the Be star probably has a significant quadrupole moment, we prefer to interpret the data by a combination of timing noise, dominated by a cubic phase term, and ω. and x. terms. We show that the ω. and x. terms are likely to be a result of a precessing orbit caused by the quadrupole moment of the tilted companion star. We further rule out a number of possible physical effects which could contribute to the timing data of PSR B1259–63 on a measurable level.

ROTATION INTRINSIC SPIN EFFECTS AND ITS ASTROPHYSICAL APPLICATION

On the basis of rotation-spin, torsion-spin and magnetic-spin effects, by which the spin precession arises the polarized magnetic field of neutron star to incline to the rotational axis. In the case of accretion layer structure of the recycled pulsar and the companion star magnetic influence considered, the magnetic inclinations of the recycled pulsars are different from that of the normal radio pulsars. The theoretical conclusions and consistent observational evidence is discussed.

The Galactic population of pulsars

We review our knowledge of the population of normal and millisecond radio pulsars in the disk of the Galaxy and in the Galactic globular cluster system. There are about 150 000 active normal pulsars in the Galaxy with luminosity exceeding 1 mJy kpc 2, a new one being born about once every 125 years with mean velocity of 400–500 km s −1. The total Galactic population of millisecond pulsars is similar in size, although the rate of formation of these is probably one every 10 5 years. There are probably about 10 000 pulsars in the globular cluster system, of which 90% are millisecond pulsars. The remaining 10% are much younger, apparently normal pulsars, and must be formed at least as frequently as the millisecond pulsars.

Galactic Gamma‐Ray Background as a Constraint on Millisecond Pulsars

A large number of millisecond pulsars are believed to exist in the Galaxy. Their magnetic fields are generally 2-4 orders of magnitude smaller than those of the normal pulsars. These pulsars are thought to have been resurrected from the run-down old pulsars. We apply the mechanism proposed by Scharlemann et al. (1978) for particle acceleration along open field lines in the magnetospheres of these pulsars and find that particles can become highly relativistic. We then calculate the γ-ray flux of curvature radiation from the accelerated particles. Since the number of millisecond pulsars in the Galaxy is quite uncertain, we survey the literature to get some estimates of the number of millisecond pulsars in the plane of the Galaxy and in the globular clusters. We use these numbers to work out the integrated high-energy γ-ray flux from millisecond pulsars in the Galaxy as a function of the Galactic latitude and longitude. We discuss the results in the light of the COS B observations of the background γ-radiation, which is the resultant diffuse emission when the contribution of the known point sources has been subtracted from the total emission, and the flux calculated by Strong et al. from the interaction of H I and H2 with cosmic rays and inverse Compton emission. We are able to place useful constraints on the number of millisecond pulsars in the disk and in the globular clusters.

Magnetic and spin evolution of pulsars

We explore the consequences of the model of spin-down-induced flux expulsion for the magnetic field evolution in solitary as well as in binary neutron stars. The spin evolution of pulsars, allowing for their field evolution according to this model, is shown to be consistent with the existing observational constraints in both low- and high-mass X-ray binary systems. The contribution from pulsars recycled in massive binaries to the observed excess in the number of low-field (10(11)-10(12) G) solitary pulsars is argued to be negligible in comparison with that of normal pulsars undergoing a 'restricted' field decay predicted by the adopted field decay model. Magnetic fields of neutron stars born in close binaries with intermediate- or high-mass main-sequence companions are predicted to decay down to values as low as similar to 10(6) G, which would leave them unobservable as pulsars during most of their lifetimes. The post-recycling evolution of some of these systems can, however, account for the observed binary pulsars having neutron star or massive white dwarf companions. Pulsars recycled in the disc population low-mass binaries are expected to have residual fields greater than or similar to 10(8) G, while for those processed in globular clusters larger residual fields are predicted because of the lower field strength of the neutron star at the epoch of binary formation. A value of tau similar to 1-2 x 10(7) yr for the mean value of the Ohmic decay time-scale in the crusts of neutron stars is suggested, based on the consistency of the model predictions with the observed distribution of periods and magnetic fields in the single and binary pulsars.

Polar Gap Dynamics and the Death Line of Millisecond Pulsars

Pulsar polar gaps are considered in which the potential drop is a significant fraction of that induced by the rotation of the neutron star. Such gaps are required in order for the observed restriction in the distribution of magnetic field strengths (B) and periods (P) in normal pulsars to be attributed to a death line beyond which the pulsar emission mechanism ceases to operate. It is shown that in contrast to normal pulsars, in which curvature radiation determines the death line, for millisecond pulsars synchrotron radiation is the dominant emission mechanism. The resulting death line is shifted to shorter periods by a factor ~3, as compared to an extrapolation of the death line for normal pulsars. The magnitude of this shift is quite model independent, since it is determined by the diterent properties of the two emission mechanisms. The transition between these different parts of the death line is caused by radiative reaction and occurs for B ~ 109?1010 G. A hitherto neglected effect forces a steepening of the death line for B 1012 G. Although quite model dependent, the same effect can account for the lack of observed millisecond pulsars with B 108 G. Except for the transition region, the location of the death line is insensitive to whether the polar gap breaks down or not. On the other hand, it is argued that both observational and theoretical results are reconciled best with a gap that breaks down, albeit only over a limited portion of the polar cap. The resemblance of the derived death line to the limits of the observed distribution of millisecond pulsars suggests that the observed values of magnetic field strengths and periods are due to the dynamics of the polar gap and not to restrictions imposed during their formation process. Since a large fraction of millisecond pulsars lie close to the derived death line, a significant number of neutron stars may exist that are not observed as millisecond pulsars. This makes the birth rate discrepancy between millisecond pulsars and their assumed low-mass X-ray binary progenitors more acute.

Populations and evolution of radio pulsars

A new physical parameter Q =log(We/P 2/3 ) is defined as a criterion for judging whether a radio pulsar is a normal pulsar or a recycled pulsar originating from accreting binary systems.Based on the definition,the observational characteristics and the evolution of the two groups of pulsars are discussed.

The death line of millisecond pulsars

AbstractThe distribution of millisecond pulsars, just as normal pulsars, is affected by a death line. Since a large fraction of millisecond pulsars lie close to the derived death line, a significant number of neutron stars may exist which are not observed as millisecond pulsars. This makes the birth rate discrepancy between millisecond pulsars and their assumed low mass x-ray binary progenitors more acute.

PSR J2019+2425 and PSR J2322+2057 and the proper motions of millisecond pulsars

view Abstract Citations (117) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS PSR J2019+2425 and PSR J2322+2057 and the Proper Motions of Millisecond Pulsars Nice, D. J. ; Taylor, J. H. Abstract Timing observations of millisecond pulsars PSR J2019+2425 and PSR J2322+2057 made over more than 2 years have yielded spin-down, astrometric, and binary parameters. The proper motions of these sources are 23.5 +/- 1.3 and 25 +/- 3 mas/yr, respectively, corresponding to transverse velocities of approximately 100 and 90 km/s. These measurements, combined with other published millisecond pulsar proper motions, indicate that the population has a velocity dispersion of order 60 km/s, comparable to that of low-mass X-ray binaries (from which millisecond pulsars evolve) but much lower than that of normal (non-millisecond) pulsars. The spin-down rates of J2019+2425 and J2322+2057 are extraordinarily low and, when biases induced by motion are removed, formal calculations yield ages of 27 x 109 and 19 x 109 yr, respectively, indicating they have evolved little since becoming millisecond pulsars. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/175367 Bibcode: 1995ApJ...441..429N Keywords: Pulsars; Stellar Motions; Velocity Distribution; X Ray Binaries; Astrometry; Chronology; Kinematics; Mathematical Models; Astrophysics; STARS: BINARIES: CLOSE; STARS: KINEMATICS; STARS: PULSARS: INDIVIDUAL ALPHANUMERIC: PSR J2019; 2425; STARS: PULSARS: INDIVIDUAL ALPHANUMERIC: PSR J2322; 2057 full text sources ADS | data products SIMBAD (2)

Are millisecond pulsars different than “Normal” pulsars?

AbstractWhile millisecond pulsars have very different period parameters and a different evolutionary history compared to “normal” pulsars, the properties of their pulsed emission are remarkably similar to those of normal pulsars.

Smothered pulsars and the central radio sources in M81, M82, and the Galaxy

view Abstract Citations (1) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Smothered Pulsars and the Central Radio Sources in M81, M82, and the Galaxy Engelke, Charles W. Abstract A model is proposed which furnishes a non-black hole based explanation of the Galactic center compact source and the similar sources at the cores of M81 and M82. It provides a demonstration that a normal young pulsar, like that which powers the Crab Nebula, is sufficient to power each of these sources. The abnormal characteristics of the sources (high power, small size, high spectral turnover frequency and lack of rapid expansion) are ascribed to the abnormal conditions found near a galactic core. Specifically, it is shown that if a point source of relativistic particles, such as a pulsar, moves through a dense, turbulent gas cloud, such as might exist near the dynamical center of a galaxy, the synchrotron emission from its vicinity has the same unusual features observed. Differences in the characteristics of the three sources considered are easily matched by adjusting only one parameter of the model, the density of the gas. In addition, unique features of the galactic center observed in other wave bands, such as the annihilation gamma line with its puzzling rapid decrease, find natural explanations in the framework of the smothered pulsar model. Certain predictions of the model should be experimentally testable in the near future. Publication: The Astrophysical Journal Pub Date: February 1988 DOI: 10.1086/165991 Bibcode: 1988ApJ...325..153E Keywords: Galactic Nuclei; Irregular Galaxies; Milky Way Galaxy; Pulsars; Radio Sources (Astronomy); Spiral Galaxies; Gamma Ray Astronomy; Gas Ionization; Pair Production; Relativistic Electron Beams; Synchrotron Radiation; Very Large Array (Vla); Astrophysics; GALAXIES: NUCLEI; PULSARS; RADIO SOURCES: GENERAL full text sources ADS | data products SIMBAD (2) NED (2)