Radio emission regions in pulsars

We study the concept of radius-to-frequency mapping using a geometrical method for the estimation of pulsar emission altitudes. The semi-empirical relationship proposed by Kijak &38; Gil is examined over three decades of radio frequency. It is argued that the emission region in a millisecond pulsar occupies the magnetosphere over a distance of up to about 30 per cent of the light-cylinder radius, and that in a normal pulsar occupies up to approximately 10 per cent of the light-cylinder radius.     

Radio pulsars in Terzan 5

We report on searches of the globular cluster Terzan 5 for low-luminosity and accelerated radio pulsars using the 64-m Parkes radio telescope. One new millisecond pulsar, designated PSR J1748−2446C, was discovered, having a period of 8.44 ms. Timing measurements using the 76-m Lovell radio telescope at Jodrell Bank show that it is a solitary pulsar and lies close to the core of the cluster. We also present the results of timing measurements which show that the longer period pulsar PSR J1748−2444 (formerly known as PSR B1744−24B) lies 10 arcmin from the core of the cluster and is unlikely to be associated with the cluster. We conclude that there are further pulsars to be detected in the cluster.     

Radio pulsars with expected gamma radiation and gamma-ray pulsars as pulsating radio emitters

Pulsars play a crucial astrophy sical role as highly energetic compact radio, X-ray and gammaray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope(LAT) on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars: log B_(lc)(G) are 3.60-3.95 and 1.75 correspondingly. Moreover,their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average: log E(erg s~(-1)) = 35.37-35.53 and 32.64. The correlation between gammaray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand,the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.     

Radio search for pulsed emission from X-ray pulsars

An experiment has been performed at 325 MHz, with a 10 m tracking dish, for the search of pulsed radio emission associated with X-ray pulsars. No evidence of radio pulses has been found in the four sources investigated, although the radio pulsar PSR 0329+54, used as a testing object, has been detected successfully.     

Hard spectra of X-ray pulsars from INTEGRAL data

We present spectra for 34 accretion-powers X-ray pulsars and one millisecond pulsar that were within the field of view of the INTEGRAL observatory over two years (December 2002–January 2005) of its in-orbit operation and that were detected by its instruments at a statistically significant level (> 8σ in the energy range 18–60 keV). There are seven recently discovered objects of this class among the pulsars studied: 2RXP J130159.6-635806, IGR/AX J16320-4751, IGR J16358-4726, AX J163904-4642, IGR J16465-4507, SAX/IGR J18027-2017, and AX J1841.0-0535. We have also obtained hard X-ray (>20 keV) spectra for the accretion-powered pulsars RX J0146.9+6121, AX J1820.5-1434, and AX J1841.0-0535 for the first time. We analyze the evolution of spectral parameters as a function of the intensity of the sources and compare these with the results of previous studies.     

Radio spectra of some markarian galaxies

Radio spectra of 16 Markarian galaxies are studied between 2.7 and 15.5 GHz. The Seyfert-type galaxies have power-law spectra with an average spectral index of -0.82, except for MRK 348, which is an active galaxy with a complex spectrum. The galaxies with featureless optical spectra have rather flat radio spectra, similar to BL Lac-type objects.     

Radio emission spectra of spiral galaxies

It is shown that objects with relatively flat radio emission spectra are mainly encountered among spiral galaxies of morphological subtypes Sa and Sab (including barred galaxies of these subtypes). Objects both with flat and with steep spectra are encountered among galaxies of morphological subtypes later than Sab. Translated from Astrofizika, Vol. 41, No. 1, pp. 35–39, January-March, 1998     

Gamma-ray pulsars: the pulse profiles and phase-resolved spectra of Geminga

We present a calculation of a three-dimensional pulsar magnetosphere model to explain high-energy emission from the Geminga pulsar with a thick outer gap. High-energy γ -rays are produced by primary accelerated particles with a power-law energy distribution through curvature radiation inside the outer gap. We also calculate the emission pattern, pulse profile and phase-resolved spectra of high-energy γ -rays of the Geminga pulsar, and find that its pulse profile is consistent with the observed one if the magnetic inclination and viewing angle are ∼50° and ∼86° respectively. We describe the relative phases among soft (thermal) X-rays, hard (non-thermal) X-rays, and γ -rays. Our results indicate that X-ray and γ -ray emission from the Geminga pulsar may be explained by the single thick outer gap model. Finally, we discuss the implications of the radio and optical emission of the Geminga pulsar.     

Radio spectra of synchrotron sources with spherical symmetry

This paper deals with the radio spectra of synchrotron sources with spherically symmetric non-homogeneities. It is pointed out that the Type-c spectra can be produced by such a non-homogeneity even if the source is optically thin. This model is particularly advantageous in interpreting sources with no compact characteristics and yet showing a Type-c spectrum, and the observed decrease in source size with increasing frequency. In addition, it is possible to give a uniform interpretation of the four spectral types on the basis of such a non-homogeneity.     

Radio spectra and polarization properties of radio-loud broad absorption-line quasars

We present multifrequency observations of a sample of 15 radio-emitting broad absorption-line quasars (BAL QSOs), covering a spectral range between 74 MHz and 43 GHz. They mostly display convex radio spectra which typically peak at about 1–5 GHz (in the observer's rest frame), flatten at MHz frequencies, probably due to synchrotron self-absorption, and become steeper at high frequencies, i.e. ν≳ 20 GHz. Very Large Array (VLA) 22-GHz maps (HPBW ∼80 mas) show unresolved or very compact sources, with linear projected sizes of ≤1 kpc. About two-thirds of the sample looks unpolarized or weakly polarized at 8.4 GHz, frequency in which reasonable upper limits could be obtained for polarized intensity. Statistical comparisons have been made between the spectral index distributions of samples of BAL and non-BAL QSOs, both in the observed and in the rest frame, finding steeper spectra among non-BAL QSOs. However, constraining this comparison to compact sources results in no significant differences between both distributions. This comparison is consistent with BAL QSOs not being oriented along a particular line of sight. In addition, our analysis of the spectral shape, variability and polarization properties shows that radio BAL QSOs share several properties common to young radio sources like compact steep spectrum or gigahertz peaked spectrum sources.     

Josephson pulsars

An emission mechanism of pulsars based on the a.c. Josephson effect, proposed by Kovalev, is critically examined. It is concluded that such a mechanism is very improbable, for reasons associated with the physics of the neutron star and of the Josephson effect.     

Recycled pulsars

Original letter published in Astrofizika, Vol. 32, No. 1, pp. 193–194, January–February, 1990.     

Gamma-ray pulsars

Various observations of γ-ray pulsars are summarized briefly and related to outer-magnetosphere accelerator models.     

Millisecond pulsars

In 1982 we discovered a pulsar with the phenomenal rotation rate of 642 Hz, 20 times faster than the spin rate of the Crab pulsar. The absence of supernova debris in the vicinity of the pulsar at any wavelength indicates an age of the neutron star greater than 10⁵ yr. The miniscule spindown rate of 1.1 × 10^-19 confirms the old age and indicates a surface magnetic field of 10⁹ G. A second millisecond pulsar was discovered by Boriakoff, Buccheri & Fauci (1983) in a 120-day orbit. These fast pulsars may have been spun-up by mass transfer in a close binary evolutionary stage. Arrival-time observations of the 642-Hz pulsar display remarkably low residuals over the first 14 months. The stability implied by these observations, 3 × 10^-14, suggests that millisecond pulsars will provide the most accurate basis for terrestrial dynamical time. If so, the pulsar data will lead to improvements in the planetary ephemeris and to new searches for light-year scale gravitational waves. Many new searches for fast pulsars are under way since previous sky surveys excluded pulsars with spins above 60 Hz.