Pulsar Dispersion Measures Research Articles

Pulsar Astrometry

High precision measurements of the celestial coordinates of pulsars are desirable for a number of reasons. If carried out at several epochs, the measurements can yield angular proper motions; together with distance estimates based on dispersion measure, the proper motion of a pulsar reveals two of three components of its space velocity, and consequently provides important kinematic information on pulsar ages (see, for example, Manchester, Taylor and Van 1974; Lyne, Anderson and Salter 1982; and references therein). Direct measurements of annual parallaxes are also possible in principle, and are marginally feasible with present techniques for a few of the closest pulsars. Model independent distances obtained from parallax measurements, together with observed pulsar dispersion measures, yield the electron density along the line of sight to the pulsar. Knowledge of the interstellar electron density in the solar neighborhood provides a calibration of the dispersion-based distance scale that is complementary to the calibration derived from neutral hydrogen absorption measurements of more distant pulsars (Weisberg et al. 1980), and permits appropriate statistical analyses to be made of the local space density of pulsars and their birthrate (e.g. Taylor and Manchester 1977). Finally, pulsar astrometry can be expected to yield important information on the relative orientations of fundamental reference frames. In particular, pulse timing observations yield positions in a reference frame based on motions of the planets, while interferometric position measurements are based on an Earth-equatorial system. At present the relative orientation of these two coordinate systems is known to only accuracy, though the potential precision of both types of measurements is much higher.

Further observations of the long-period binary pulsar PSR 0820+02

view Abstract Citations (24) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Further observations of the long-period binary pulsar PSR 0820+02. Manchester, R. N. ; Newton, L. M. ; Cooke, D. J. ; Backus, P. R. ; Damashek, M. ; Taylor, J. H. ; Condon, J. J. Abstract Observations of the second known orbiting pulsar, PSR 0820+02, now span just over 4 years, an interval comparable to the orbital period. Analysis of pulse arrival time data has produced accurate values of the celestial coordinates of the system, as well as the pulsar dispersion measure, period, slowdown rate, and orbital elements. The pulsar's position was also determined interferometrically by using the VLA, with results in accord with the timing data to better than the combined errors. We discuss briefly the possible evolution of this orbiting system. Publication: The Astrophysical Journal Pub Date: May 1983 DOI: 10.1086/161005 Bibcode: 1983ApJ...268..832M Keywords: Binary Stars; Orbital Elements; Pulsars; Stellar Evolution; Astronomical Maps; Interferometry; Position (Location); Astronomy full text sources ADS | data products SIMBAD (1)

Discovery of radio pulsations from the X-ray pulsar in the supernova remnant G320.4-1.2

A radio counterpart to the X-ray pulsar discovered by Seward and Harnden in the supernova remnant G320.4-1.2 (MSH 15--52) has been detected. The radio observations confirm the very large period derivative indicated by the X-ray data. This implies that the object is not a member of a binary system and hence is an isolated pulsar similar in some ways to the Crab pulsar. Association of the pulsar and the supernova remnant is supported by the observed pulsar dispersion measure.

The distribution of free electrons in the inner Galaxy from pulsar dispersion measures

The dispersion measures of a sample of 149 pulsars in the inner Galaxy (absolute value of l 50 deg) were statistically analyzed to deduce the large-scale distribution of free thermal electrons in this region. The dispersion measure distribution of these pulsars shows significant evidence for a decrease in the electron scale height from a local value greater than the pulsar scale height to a value less than the pulsar scale height at galactocentric radii inside of approximately 7 kpc. An increase in the electron density (to a value around .15/cu cm at 4 to 5 kpc) must accompany such a decrease in scale height. There is also evidence for a large-scale warp in the electron distribution below the b + 0 deg plane inside the Solar circle. A model is proposed for the electron distribution which incorporates these features and Monte Carlo generated dispersion measure distributions are presented for parameters which best reproduce the observed pulsar distributions.

Introduction to the session

Five years ago, at the previous IAU Symposium (No. 60) on the galaxy, most of us pictured the interstellar medium (ISM) as a mainly quiescent medium which evolved by orderly processes–the “steady state” ISM. Radhakrishnan reviewed the “intercloud medium” which was warm (some few thousand degrees), rarefied (some few tenths cm−3), uniformly - distributed, partly ionized, and responsible for the smoothly-distributed pulsar dispersion measures and Faraday rotations. Heiles reviewed the “clouds,” which had densities of tens cm−3, temperatures of tens K, and nonspherical shapes. These two components were in approximate pressure equilibrium; Grewing, in his review of heating mechanisms, emphasized pervasive, nonvarying processes.

Pulsar dispersion measures and H-alpha emission measures - Limits on the electron density and filling factor for the ionized interstellar gas

Pulsar dispersion measures and H-alpha emission measures - Limits on the electron density and filling factor for the ionized interstellar gas

Pulsars: Observational parameters and a discussion on dispersion measures

The relevant data for the known 147 pulsars are presented in graphical and tabular forms. Various data correlations are discussed, and a detailed analysis of pulsar dispersion measures and distances is given. The range of the electron densities in the diffuse interstellar medium is found to be 0.01 cm−3≲n e≲0.1 cm−3, and 〈n e〉≃0.03 cm−3. The dispersion scale height for pulsars is found to be ∼5.9±0.7 pc cm−3 implying a linear scale height of ∼200 pc, which is much smaller than the electron scale height of our Galaxy.

The termination of the solar wind

It has previously been suggested that the solar wind might terminate at distances of 5 AU to 20 AU from the Sun, and that the solar wind might be drastically slowed down by charge exchange and photoionization of interstellar hydrogen atoms which approach the Sun. However, recent satellite measurements of resonantly scattered Lyman alpha radiation, together with pulsar dispersion and Faraday rotation measures, imply very small values for the interstellar hydrogen density (0.05 cm −3) and magnetic field strength (3 μG). As a result, the solar wind is not expected to be slowed down by more than about 30% inside the termination distance, which is expected to be about 100 AU. Analytic solutions for the solar wind flux and velocity as a function of distance have been obtained, yielding estimates of the slowing down and termination distance as a function of the various input parameters (solar wind flux, velocity, solar Lyman-continuum flux, interstellar hydrogen density and velocity, and magnetic field strength).

Pulsar dispersion measures and the mean and mean-squared interstellar electron density

Theoretical distributions of pulsar dispersion measures (times sinbII) are computed for various assumed pulsar spatial distributions above (and below) the galactic plane, assuming a distribution for the ionized gas. The statistics on the twelve high-latitude pulsars lead to the conclusion that the pulsar distribution inz is at least as broad as the distribution of the ionized gas. The value derived for the local mean interstellar electron density in the galactic plane is 0.12 cm−3 and is interpreted to be due to a uniform ionized intercloud medium.