Formation of "Lightnings" in a Neutron Star Magnetosphere and the Nature of RRATs

The connection between the radio emission from "lightnings" produced by the absorption of high-energy photons from the cosmic gamma-ray background in a neutron star magnetosphere and radio bursts from rotating radio transients (RRATs) is investigated. The lightning length reaches 1000 km; the lightning radius is 100 m and is comparable to the polar cap radius. If a closed magnetosphere is filled with a dense plasma, then lightnings are efficiently formed only in the region of open magnetic field lines. For the radio emission from a separate lightning to be observed, the polar cap of the neutron star must be directed toward the observer and, at the same time, the lightning must be formed. The maximum burst rate is related to the time of the plasma outflow from the polar cap region. The typical interval between two consecutive bursts is ~100 s. The width of a single radio burst can be determined both by the width of the emission cone formed by the lightning emitting regions at some height above the neutron star surface and by a finite lightning lifetime. The width of the phase distribution for radio bursts from RRATs, along with the integrated pulse width, is determined by the width of the bundle of open magnetic field lines at the formation height of the radio emission. The results obtained are consistent with the currently available data and are indicative of a close connection between RRATs, intermittent pulsars, and extreme nullers.Comment: 24 pages, no figures, references update

Phase and Intensity Distributions of Individual Pulses of PSR B0950+08

The distribution of the intensities of individual pulses of PSR B0950+08 as a function of the longitudes at which they appear is analyzed. The flux density of the pulsar at 111 MHz varies strongly from day to day (by up to a factor of 13) due to the passage of the radiation through the interstellar plasma (interstellar scintillation). The intensities of individual pulses can exceed the amplitude of the mean pulse profile, obtained by accumulating 770 pulses, by more than an order of magnitude. The intensity distribution along the mean profile is very different for weak and strong pulses. The differential distribution function for the intensities is a power law with index n = -1.1 +- 0.06 up to peak flux densities for individual pulses of the order of 160 Jy

The spark-associated soliton model for pulsar radio emission

We propose a new, self-consistent theory of coherent pulsar radio emission based on the non-stationary sparking model of Ruderman & Sutherland (1975), modified by Gil & Sendyk (2000) in the accompanying Paper I. According to these authors, the polar cap is populated as densely as possible by a number of sparks with a characteristic perpendicular dimension D approximately equal to the polar gap height scale h, separated from each other also by about h. Each spark reappears in approximately the same place on the polar cap for a time scale much longer than its life-time and delivers to the open magnetosphere a sequence of electron-positron clouds which flow orderly along a flux tube of dipolar magnetic field lines. The overlapping of particles with different momenta from consecutive clouds leads to effective two-stream instability, which triggers electrostatic Langmuir waves at the altitudes of about 50 stellar radii. The electrostatic oscillations are modulationally unstable and their nonlinear evolution results in formation of ``bunch-like'' charged solitons. A characteristic soliton length along magnetic field lines is about 30 cm, so they are capable of emitting coherent curvature radiation at radio wavelengths. The net soliton charge is about 10^21 fundamental charges, contained within a volume of about 10^14 cm^3. For a typical pulsar, there are about 10^5 solitons associated with each of about 25 sparks operating on the polar cap at any instant. One soliton moving relativisticaly along dipolar field lines with a Lorentz factor of the order of 100 generates a power of about 10^21 erg/s by means of curvature radiation. Then the total power of a typical radio pulsar can be estimated as being about 10^(27-28) erg/s.Comment: 27 pages, 5 figures, accepted by Ap

Review of scientific topics for Millimetron space observatory

This paper describes outstanding issues in astrophysics and cosmology that can be solved by astronomical observations in a broad spectral range from far infrared to millimeter wavelengths. The discussed problems related to the formation of stars and planets, galaxies and the interstellar medium, studies of black holes and the development of the cosmological model can be addressed by the planned space observatory Millimetron (the "Spectr-M" project) equipped with a cooled 10-m mirror. Millimetron can operate both as a single-dish telescope and as a part of a space-ground interferometer with very long baseline.Comment: The translation of the original article in Physics Uspekhi http://ufn.ru/ru/articles/2014/12/c

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

Lower Bound on the Magnetic Field Strength of a Magnetar from Analysis of SGR Giant Flares

Based on the magnetar model, we have studied in detail the processes of neutrino cooling of an electron--positron plasma generating an SGR giant flare and the influence of the magnetar magnetic field on these processes. Electron--positron pair annihilation and synchrotron neutrino emission are shown to make a dominant contribution to the neutrino emissivity of such a plasma. We have calculated the neutrino energy losses from a plasma-filled region at the long tail stage of the SGR 0526--66, SGR 1806--20, and SGR 1900+14 giant flares. This plasma can emit the energy observed in an SGR giant flare only in the presence of a strong magnetic field suppressing its neutrino energy losses. We have obtained a lower bound on the magnetic field strength and showed this value to be higher than the upper limit following from an estimate of the magnetic dipole losses for the magnetars being analyzed in a wide range of magnetar model parameters. Thus, it is problematic to explain the observed energy release at the long tail stage of an SGR giant flare in terms of the magnetar model.Comment: 18 pages, 5 figure

Interstellar Plasma Turbulence Spectrum Toward the Pulsars PSR B0809+74 and B0950+08

Interstellar scintillations of pulsars PSR B0809+74 and B0950+08 have been studied using observations at low frequencies (41, 62, 89, and 112 MHz). Characteristic temporal and frequency scales of diffractive scintillations at these frequencies have been determined. The comprehensive analysis of the frequency and temporal structure functions reduced to the same frequency has shown that the spectrum of interstellar plasma inhomogeneities toward both pulsars is described by a power law. The exponent of the spectrum of fluctuations of interstellar plasma inhomogeneities toward PSR B0950+08 (n = 3.00 +- 0.05) appreciably differs from the Kolmogorov exponent. Toward PSR B0809+74 the spectrum is a power law with an exponent n = 3.7 +- 0.1. A strong angular refraction has been detected toward PSR B0950+08. The distribution of inhomogeneities along the line of sight has been analyzed; it has been shown that the scintillations of PSR B0950+08 take place on a turbulent layer with enhanced electron density, which is localized at approximately 10 pc from the observer. For PSR B0809+74 the distribution of inhomogeneities is quasi-uniform. Mean-square fluctuations of electron density on inhomogeneities with a characteristic scale rho_0 = 10^7 m toward four pulsars have been estimated. On this scale the local turbulence level in the 10-pc layer is 20 times higher than in an extended region responsible for the scintillations of PSR B0809+74.Comment: 13 pages, 11 figure

The LOFAR pilot surveys for pulsars and fast radio transients

We have conducted two pilot surveys for radio pulsars and fast transients with the Low-Frequency Array (LOFAR) around 140 MHz and here report on the first low-frequency fast-radio burst limit and the discovery of two new pulsars. The first survey, the LOFAR Pilot Pulsar Survey (LPPS), observed a large fraction of the northern sky, ~1.4 x 10^4 sq. deg, with 1-hr dwell times. Each observation covered ~75 sq. deg using 7 independent fields formed by incoherently summing the high-band antenna fields. The second pilot survey, the LOFAR Tied-Array Survey (LOTAS), spanned ~600 sq. deg, with roughly a 5-fold increase in sensitivity compared with LPPS. Using a coherent sum of the 6 LOFAR "Superterp" stations, we formed 19 tied-array beams, together covering 4 sq. deg per pointing. From LPPS we derive a limit on the occurrence, at 142 MHz, of dispersed radio bursts of 107 Jy for the narrowest searched burst duration of 0.66 ms. In LPPS, we re-detected 65 previously known pulsars. LOTAS discovered two pulsars, the first with LOFAR or any digital aperture array. LOTAS also re-detected 27 previously known pulsars. These pilot studies show that LOFAR can efficiently carry out all-sky surveys for pulsars and fast transients, and they set the stage for further surveying efforts using LOFAR and the planned low-frequency component of the Square Kilometer Array.Comment: 18 pages, 10 figures, accepted for A&