The Characteristics of (Normal) Pulsars

Pulsars have now been studied for 34 years. We know of the existence of some 1500 objects at radio frequencies. Many of the characteristics of pulsars such as pulsar period, period derivative, spectrum, polarization, etc., have been catalogued for many objects. Still we do not know the details of the pulsar emission mechanism. The present review will give an up-to-date description of the characteristics of (normal, slow) radio pulsars. Millisecond pulsars will be dealt with by M. Kramer (this volume).Comment: 4 pages, 4 figures. To appear in the Proceedings of the 270. WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants, Jan. 21-25, 2002, Physikzentrum Bad Honnef, eds W. Becker, H. Lesch & J. Truemper. Proceedings are available as MPE-Report 27

Magnetic Fields in the Milky Way and in Galaxies

Most of the visible matter in the Universe is ionized, so that cosmic magnetic fields are quite easy to generate and due to the lack of magnetic monopoles hard to destroy. Magnetic fields have been measured in or around practically all celestial objects, either by in-situ measurements of spacecrafts or by the electromagnetic radiation of embedded cosmic rays, gas, or dust. The Earth, the Sun, solar planets, stars, pulsars, the Milky Way, nearby galaxies, more distant (radio) galaxies, quasars, and even intergalactic space in clusters of galaxies have significant magnetic fields, and even larger volumes of the Universe may be permeated by 'dark' magnetic fields. Information on cosmic magnetic fields has increased enormously as the result of the rapid development of observational methods, especially in radio astronomy. In the Milky Way, a wealth of magnetic phenomena was discovered that are only partly related to objects visible in other spectral ranges. The large-scale structure of the Milky Way's magnetic field is still under debate. The available data for external galaxies can well be explained by field amplification and ordering via the dynamo mechanism. The measured field strengths and the similarity of field patterns and flow patterns of the diffuse ionized gas give strong indication that galactic magnetic fields are dynamically important. They may affect the formation of spiral arms, outflows, and the general evolution of galaxies. In spite of our increasing knowledge on magnetic fields, many important questions on the origin and evolution of magnetic fields, like their first occurrence in young galaxies, or the existence of large-scale intergalactic fields remained unanswered. The present upgrades of existing instruments and several radio astronomy projects have defined cosmic magnetism as one of their key science projects.Comment: Revised version of Chapter 13 in "Planets, Stars and Stellar Systems", Vol. 5: "Galactic Structure and Stellar Populations", ed. G. Gilmore, Springer, Berlin 2013, ISBN 978-90-481-8817-

Pulsar spectra of radio emission

We have collected pulsar flux density observations and compiled spectra of 281 objects. The database of Lorimer et al. (\cite{lorimer}) has been extended to frequencies higher than 1.4 GHz and lower than 300 MHz. Our results show that above 100 MHz the spectra of the majority of pulsars can be described by a simple power law with average value of spectral index $= -1.8\pm0.2$. A rigorous analysis of spectral fitting revealed only about 5% of spectra which can be modelled by the two power law. Thus, it seems that single power law is a rule and the two power law spectrum is a rather rare exception, of an unknown origin, to this rule. We have recognized a small number of pulsars with almost flat spectrum ($\alpha \geq -1.0$) in the wide frequency range (from 300 MHz to 20 GHz) as well as few pulsars with a turn-over at unusually high frequency ($\sim$~1 GHz).Comment: 9 pages, 3 figure

Shapiro delay in the PSR J1640+2224 binary system

We present the results of precision timing observations of the binary millisecond pulsar PSR J1640+2224. Combining the pulse arrival time measurements made with the Effelsberg 100-m radio telescope and the Arecibo 305-m radio telescope, we have extended the existing timing model of the pulsar to search for a presence of the effect of a general-relativistic Shapiro delay in the data. At the currently attainable precision level, the observed amplitude of the effect constrains the companion mass to m_2=0.15^{+0.08}_{-0.05} M_\sun, which is consistent with the estimates obtained from optical observations of the white dwarf companion and with the mass range predicted by theories of binary evolution. The measured shape of the Shapiro delay curve restricts the range of possible orbital inclinations of the PSR J1640+2224 system to $78^{\circ}\le i\le 88^{\circ}$. The pulsar offers excellent prospects to significantly tighten these constraints in the near future.Comment: 12 pages, 4 figures, accepted for publication in Ap

Morphology and characteristics of radio pulsars

This review describes the observational properties of radio pulsars, fast rotating neutron stars, emitting radio waves. After the introduction we give a list of milestones in pulsar research. The following chapters concentrate on pulsar morphology: the characteristic pulsar parameters such as pulse shape, pulsar spectrum, polarization and time dependence. We give information on the evolution of pulsars with frequency since this has a direct connection with the emission heights, as postulated in the radius to frequency mapping (RFM) concept. We deal successively with the properties of normal (slow) pulsars and of millisecond (fast-recycled) pulsars. The final chapters give the distribution characteristics of the presently catalogued 1300 objects.Comment: 33 pages, PDF with 30 PostScript figures, see http://springerlink.metapress.com/link.asp?id=d6k3a6wunb138dpl Accepted by Astronomy & Astrophysivs Review

The characteristics of millisecond pulsar emission: I. Spectra, pulse shapes and the beaming fraction

We have monitored a large sample of millisecond pulsars using the 100-m Effelsberg radio telescope in order to compare their radio emission properties to the slowly rotating population. With some notable exceptions, our findings suggest that the two groups of objects share many common properties. A comparison of the spectral indices between samples of normal and millisecond pulsars demonstrates that millisecond pulsar spectra are not significantly different from those of normal pulsars. There is evidence, however, that millisecond pulsars are slightly less luminous and less efficient radio emitters compared to normal pulsars. We confirm recent suggestions that a diversity exists among the luminosities of millisecond pulsars with the isolated millisecond pulsars being less luminous than the binary millisecond pulsars. There are indications that old millisecond pulsars exhibit somewhat flatter spectra than the presumably younger ones. We present evidence that millisecond pulsar profiles are only marginally more complex than those found among the normal pulsar population. Moreover, the development of the profiles with frequency is rather slow, suggesting very compact magnetospheres. The profile development seems to anti-correlate with the companion mass and the spin period, again suggesting that the amount of mass transfer in a binary system might directly influence the emission properties. The angular radius of radio beams of millisecond pulsars does not follow the scaling predicted from a canonical pulsar model which is applicable for normal pulsars. Instead they are systematically smaller. The smaller inferred luminosity and narrower emission beams will need to be considered in future calculations of the birth-rate of the Galactic population.Comment: 40 pages, 14 figures, accepted for publication in Ap

Milestones in the Observations of Cosmic Magnetic Fields

Magnetic fields are observed everywhere in the universe. In this review, we concentrate on the observational aspects of the magnetic fields of Galactic and extragalactic objects. Readers can follow the milestones in the observations of cosmic magnetic fields obtained from the most important tracers of magnetic fields, namely, the star-light polarization, the Zeeman effect, the rotation measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio polarization observations, as well as the newly implemented sub-mm and mm polarization capabilities. (Another long paragraph is omitted due to the limited space here)Comment: Invited Review (ChJA&A); 32 pages. Sorry if your significant contributions in this area were not mentioned. Published pdf & ps files (with high quality figures) now availble at http://www.chjaa.org/2002_2_4.ht

The characteristics of millisecond pulsar emission: II. Polarimetry

We have made polarimetric monitoring observations of millisecond pulsars visible from the northern hemisphere at 1410 MHz. Their emission properties are compared with those of normal pulsars. Although we demonstrated in paper I that millisecond pulsars exhibit the same flux density spectra and similar profile complexity, our results presented here suggest that millisecond pulsar profiles do not comply with the predictions of classification schemes based on ``normal'' pulsars. The frequency development of a large number of millisecond pulsar profiles is abnormal when compared with the development seen for normal pulsars. Moreover, the polarization characteristics suggest that millisecond-pulsar magnetospheres might not simply represent scaled versions of the magnetospheres of normal pulsars, supporting results of paper I. However, phenomena such as mode-changing activity in both intensity and polarization are recognized here for the first time (e.g., J1730--2304). This suggests that while the basic emission mechanism remains insensitive to rotational period, the conditions that, according to the canonical pulsar model, regulate the radio emission, might be satisfied at different regions in millisecond pulsar magnetospheres. At least three types of model have been proposed to describe the millisecond pulsar magnetospheres. A comparison of the predictions of these models with the observations suggests that individual cases are better explained by different processes. However, we show that millisecond pulsars can be grouped according to common emission properties, a grouping that awaits verification from future multifrequency observations.Comment: 38 pages, 8 figures, accepted for publication in ApJ, (see astro-ph/9801177 for paper I