Recent observations of the decimetric radio emission from Jupiter

The position angle of linear polarization and the degree of circular polarization of the decimetric emission show no marked variations with time, although there may be an indication in the position angle data of a secular decrease in the inclination of the magnetic field structure. High resolution observations of the radiation belts show that the asymmetry in the emission found in synthesis maps originates from an extended region. The presence of this features accounts well for the observed variation in the position of the centroid of the emission with rotation. The radio observations suggest that any equatorial displacement of the main magnetic field structure from the center of the planet is less than 0.05 R_J.     

High resolution observations of the radio emission from luminous YSOs

New, high-resolution 1.66 GHz MERLIN maps of Cep A2 and LkH101 are presented and discussed.     

Small-scale galactic emission fluctuation observations with RATAN-600 radio telescope

We present the estimates of Galactic synchrotron and free-free emission power at intermediate and small scales (500 < l < 1000, 20′ < θ < 40′), based on the RATAN-600 radio telescope observations (SAO RAS). The observations were conducted in the frequency range of 2.3–11.2 GHz using the transit scan mode, in the declination range of 40.7° s δ < 42.3°. The power spectrum estimates of synchrotron and free-free components were obtained. They can be further used in the data processing stage of the high-resolution cosmological experiments like Planck.     

Super resolution for astronomical observations

In order to obtain detailed information from multiple telescope observations a general blind super-resolution (SR) reconstruction approach for astronomical images is proposed in this paper. A pixel-reliability-based SR reconstruction algorithm is described and implemented, where the developed process incorporates flat field correction, automatic star searching and centering, iterative star matching, and sub-pixel image registration. Images captured by the 1-m telescope at Yunnan Observatory are used to test the proposed technique. The results of these experiments indicate that, following SR reconstruction, faint stars are more distinct, bright stars have sharper profiles, and the backgrounds have higher details; thus these results benefit from the high-precision star centering and image registration provided by the developed method. Application of the proposed approach not only provides more opportunities for new discoveries from astronomical image sequences, but will also contribute to enhancing the capabilities of most spatial or ground-based telescopes.     

Some results of solar radio emission observations at the Siberian Solar Radio Telescope

This paper gives the main characteristics of the Siberian Solar Radio Telescope as well as some results derived by investigating the s-component sources and radio bursts on the Sun using the SSRT.     

The surface of Mercury from ground-based astronomical observations

Recent ground-based astronomical short-exposure observations of Mercury have yielded more than 50000 electronic pictures of the planet at different phases and different positions relative to the Earth. The work was fulfilled in several observatories. The use of available and newly developed processing methods applied to large volumes of electronic frames allowed the images of a considerable portion of Mercury’s surface to be synthesized. We present the images of the 90°–180°W, 215°–280°W, and 50°–90°W sectors containing, among others, the longitudes not covered by spacecraft imaging. Along with the listed images, we present the results of recent observations of Mercury carried out on November 20–24, 2006 during the morning elongation at the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) (Nizhnii Arkhyz, Karachai-Circassia, the Caucasus). The 265°–350°W longitude sector of Mercury was observed. The observations were made under good weather conditions. Among the main tasks of the new observations was obtaining a complete view of the S Basin. Previously, this basin had been investigated in fragments only by the actual solar illumination conditions. During the period of November 20–24, 2006, the S Basin was on the sunlit side of the planet. The complete image of the basin was obtained from the processing of a large number of electronic frames. The appearance of the S Basin is compared with the data on its relief acquired with radar methods. In this longitude sector, a number of other unusual surface features were found; among them, are a huge “Medallion” crater and other formations. The results considered in the present and earlier published studies are compared with the Mariner 10 data (1974–1975) and with the data received from the Messenger spacecraft during its first flyby of the planet (January 2008).     

Pulsar radio emission

The theory of pulsar radio emission has been developed in a series of our papers since 1992. It was shown that pulsar radio emission is produced in the lower part of a channel of open magnetic field lines, in a region with a height h ≈ 1.1-10⁷ μ ₃₀ ^1/3 /P^4/21 cm above a magnetic cap of the neutron star (P is the pulsar’s period and μ is the star’s magnetic moment). Here, owing to vigorously occurring processes (the production of photons of curvature radiation and their annihilation into e⁺e^- pairs), two ultrarelativistic particle fluxes are formed: an electron flux moving upward and a positron flux falling onto the star’s magnetic cap. These main fluxes are accompanied by narrow strips of positron and electron fluxes of relatively low energy, the curvature emission from which is a strong coherent radio source. The present paper is a review of earlier papers, and important additions and refinements are also made. Equations are offered for the radio luminosity of a pulsar, the solid angle of the radio beam, and the magnetic moment and moment of inertia of the pulsar’s neutron star. Translated from Astrofizika, Vol. 43, No. 1, pp. 147-169, January–March, 2000.     

Pulsar radio emission

Radio emission by pulsars is calculated from first principles. In an almost current-free magnetosphere, the two charged components (of the unsteadily escaping pair plasma) have different (and varying) bulk Lorentz factors. Curvature radiation emitted by the more energetic component is thus locally coherent, (so-called antenna mechanism). Strong enough seed signals cause the relativistically streaming charges to enhance their radiation, via an induced drift that can largely exceed the curvature drift. This amplification mechanism is similar to - but different from - that of a maser; we call it a MAIDER. Maximal amplification occurs at an (emission) altitude where the two components have sufficiently separated in energy though not yet separated too strongly in space.     

Pulsar radio emission

A new version of the theory of pulsar radio emission is developed for the case of a coaxial rotator. It is based on the electric field that we established [G. S. Sahakian, Astrofizika, 37, 97 (1994)] for the radiation channel (the channel of open magnetic field lines) and on convenient approximations for the electron energy obtained in [G. S. Sahakian and É. S. Chubarian, Astrofizika, 37, 255 (1994)]. It is shown that, owing to the emission of photons of curvature radiation by particles, e e+_c', and photon annihilation, _c e⁺e^– in the lower part of the radiation channel, a special region (the magnetic funnel) is formed in which vigorous cascade multiplication of particles occurs. The height of the magnetic funnel is h 6R^0.2, where R is the radius of the neutron star and is its angular rotation rate. As a result of supersaturation of the plasma density in the magnetic funnel, a discharge occurs after each time intervalt5·10^–7–0.8B ₁₂ ^–1.4 R ₆ ^–0.2 , i.e., the longitudinal electric field disappears (B is the magnetic induction in the star). During the active radiative processes in the magnetic funnel, two main fluxes of particles with high ultrarelativistic energies are formed: an upward flux of electrons and a positron flux falling onto the star's magnetic cap. These fluxes are accompanied by narrow strips of positron and electron fluxes, respectively, of considerably lower energy, which are fairly powerful, coherent radio sources. The pulsar's radio luminosity is calculated to be L7.4·10^223.8 ₃₀ ³ R ₆ ^–2 erg/sec, where =BR 3/2 is the star's magnetic moment. Comparing this result with observations, we conclude that the magnetic moment and hence the mass of the neutron star evidently must be considerably smaller, on the average, for fast pulsars than for slow ones. It is shown that the magnetic moment of the neutron star can be determined from the intervals between micropulses in the pulse profiles. The problem of the origin of the macrostructure of the radio pulse is discussed.Translated from Astrofizika, Vol. 38, No. 1, pp. 141–185, January – March, 1995.     

A new spectrum analyzer for radio astronomical studies with the radio telescope RATAN-600

The spectral measuring facility with a new Fourier analyzer for use with the radio telescope RATAN-600 is described and its experimental data are reported.     

Laboratory measurements of super-resolving Toraldo pupils for radio astronomical applications

The concept of super-resolution refers to various methods for improving the angular resolution of an optical imaging system beyond the classical diffraction limit. Although several techniques to narrow the central lobe of the illumination Point Spread Function have been developed in optical microscopy, most of these methods cannot be implemented on astronomical telescopes. A possible exception is represented by the variable transmittance filters, also known as “Toraldo Pupils” (TPs) since they were introduced for the first time by G. Toraldo di Francia in 1952 (Toraldo di Francia, Il Nuovo Cimento (Suppl.) 9, 426, 1952). In the microwave range, the first successful laboratory test of TPs was performed in 2003 (Mugnai et al. Phys. Lett. A 311, 77–81, 2003). These first results suggested that TPs could represent a viable approach to achieve super-resolution in Radio Astronomy. We have therefore started a project devoted to a more exhaustive analysis of TPs, in order to assess their potential usefulness to achieve super-resolution on a radio telescope, as well as to determine their drawbacks. In the present work we report on the results of extensive microwave measurements, using TPs with different geometrical shapes, which confirm the correctness of the first experiments in 2003. We have also extended the original investigation to carry out full-wave electromagnetic numerical simulations and also to perform planar scanning of the near-field and transform the results into the far-field.     

Ionospheric refraction in radio source observations at long radio wavelengths

Ionospheric refraction effects encountered in radio source observations in the 30 to 75 MHz range with the Clark Lake TPT telescope are discussed. It is found that simple calibration procedures are sufficient to provide positions of unknown sources with an accuracy of approximately one arcmin. Observations made near sunrise, or during disturbed ionospheric conditions must be discarded. If no corrections are applied, RMS errors of a few arcmin are to be expected. On leave at Radiosterrenwacht Dwingeloo, The Netherlands     

Balloon observations of fast intensity fluctuations and flare-like enhancements of X-ray emission from Cygnus X-1

The paper presents the results of the investigation on the short term X-ray emission characteristics of Cyg X-1 in the 20–150 keV range. The observations were made with balloon-borne oriented scintillation telescope and the flights were conducted from Hyderabad, India. The source was tracked over a duration of 1 hr that enabled detailed observations with time resolution of the order of 1 min. Fluctuations in the intensity of Cyg X-1 with time scales of the order of minutes have been detected besides short-term flare-like enhancements. The spectral characteristics of the flare emission features are discussed and their relationship to the phase of the binary is examined.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

Antenna data storage concept for phased array radio astronomical instruments

Low frequency Radio Astronomy instruments like LOFAR and SKA-LOW use arrays of dipole antennas for the collection of radio signals from the sky. Due to the large number of antennas involved, the total data rate produced by all the antennas is enormous. Storage of the antenna data is both economically and technologically infeasible using the current state of the art storage technology. Therefore, real-time processing of the antenna voltage data using beam forming and correlation is applied to achieve a data reduction throughout the signal chain. However, most science could equally well be performed using an archive of raw antenna voltage data coming straight from the A/D converters instead of capturing and processing the antenna data in real time over and over again. Trends on storage and computing technology make such an approach feasible on a time scale of approximately 10 years. The benefits of such a system approach are more science output and a higher flexibility with respect to the science operations. In this paper we present a radically new system concept for a radio telescope based on storage of raw antenna data. LOFAR is used as an example for such a future instrument.     

HartRAO observations of glitches in radio pulsars

Results of regular monitoring of radio pulsars over the past ten years are described. Several glitches in PSR 0833-45 and PSR 1641-45 have been observed.     

Theory of pulsar radio emission

Erevan State University. Translated from Astrofizika, Vol. 36, No. 1, pp. 87–107, January–February, 1993.     

Ultraviolet observations of Mars made by the orbiting astronomical observatory

Ultraviolet albedos of Mars in the region γγ2000–3600 Å are discussed. When the reflectivity due to the known amount of CO₂ on Mars is accounted for, the remaining reflectivity may be used to set an upper limit for the surface albedo. The result disagrees qualitatively with published ultraviolet reflectivities of limonite and carbon suboxide. An alternate interpretation of the observations leads to the conclusion that CO₂ comprises at least 60% of the molecular atmosphere of Mars, assuming the remainder to be argon. A comparison of the OAO results with 1969 Mariner ultraviolet data reveals some important areas of conflict.Attempts to detect Mars at wavelengths less than γ2000 Å were unsuccessful, with only very high upper limits being set.     

Global seasonal atmospheric fluctuations on Mars

The Mariner 9 S-band radio occultation measurements, which were taken over half a Martian year, were examined for seasonal variations in atmospheric pressures and temperatures. Seasonally related atmospheric pressure oscillations on a global scale were discovered when the pressures were compared on equi-potential levels. There was a global increase in pressure of about 13% between northern winter and spring seasons, and a global decrease in pressure of nearly 14% between northern spring and summer seasons. The maximum global pressure occurred during the northern spring season approximately one Martian month prior to aphelion. These pressure oscillations were correlated with the seasonal growth and decay, and the total area of the polar caps.Temperatures in the mid-latitude regions near the subsolar points were highest during the northern winter season when Mars was closest to the sun. In addition, high latitudinal temperature gradients (up to 2°K per degree latitude) were found. This has important atmospheric dynamical implications, especially for the growth of baroclinic waves.Occultation observations also indicated that the average elevation of the southern hemisphere was nearly 4km higher than the northern hemisphere when referenced to an equipotential level. The occultation measurements showed that the atmospheric pressures near the surface in the southern hemisphere were 33 to 43% lower than the atmospheric pressures near the surface in the northern hemisphere. In addition to other parameters, the asymmetry in the density of the Martian atmosphere and the hemispheric altitude differences are important in understanding the seasonal dynamic processes that exist in the polar cap regions and in the Martian atmosphere generally.