V. A. Samodurov

A sky survey at 102.5 MHz: Radio sources at declinations 27.5°–33.5° and 67.5°–70.5°

The results of observations on the Large Phased Array of the Lebedev Physical Institute made as part of a survey of the northern sky at 102.5 MHz are reported. Survey source lists for the declination ranges 27.5°–33.5° and 67.5°–70.5° are given, together with their coordinates, flux densities, and identifications with 4C objects. In total, there are 920 sources with flux densities S102.5≥3.0 Jy in the two zones, which cover 0.73 star. The observing and data-reduction methods are described, and the reliability and completeness of the catalog are estimated.

The search for giant radio galaxies in the PS 102 survey

The possibility of selecting extended radio sources that are potential candidates for giant radio galaxies among objects in the Pushchino catalog at 102 MHz is considered. The method used is based on the analysis of objects in a α1–α2 diagram, where α1 and α2 are two-frequency spectral indices (Sν ∼ ν−α), formally calculated using 102–365 and 365–1400 MHz data, based on the identifications of Pushchino radio sources with objects of the Texas (365 MHz) and Green Bank (1400 MHz) catalogs. The calculated spectra are abnormally steep at 102–365 MHz and flat or even inverted at 365–1400 MHz, due to the fact that the 365-MHz flux densities of extended radio sources measured with the Texas radio interferometer are appreciably underestimated. Ten objects among the fifteen Pushchino radio sources selected using this criterion proved to be already known large radio galaxies. The possibility of improving the efficiency of the method by using larger samples and applying some additional criteria selecting candidate giant radio galaxies is considered.

INTERNATIONAL LOW-FREQUENCY VERY-LONG-BASELINE INTERFEROMETRY NETWORK PROJECT MILESTONES

The low-frequency very-long-baseline interferometry network (LFVN) project was started in 1996, having the purpose to arrange the international very-long-baseline interferometry (VLBI) cooperation with participation of former Soviet Union radio telescopes. Currently there are three directions of LFVN development: a Mk 2 subsystem at 92 cm wavelength for solar research, an international S2 ad hoc array at 18 cm for active Galactic nuclei and OH-maser survey, and VLBI radar at 6 cm for investigation of Solar System bodies. 14 VLBI experiments were carried out using various combinations of radio telescopes in Canada, China, England, India, Italy, Japan, Latvia, Poland, Russia, South Africa, Ukraine and USA. The five sessions were processed by the Jet Propulsion Laboratory (California Institute of Technology) Block II and Dominion Radio Astrophysics Laboratory Penticton correlators. The Russian Mk 2 correlator in Nizhny Novgorod is under development. The paper describes the main project milestones, results ob...

Detection of sources of periodic radio emission with the Large Phased Array of the Lebedev Physical Institute

A method for searching for new periodic radio sources is described. The method is based on the spectral analysis of data from daily monitoring of the sky on the Large Phased Antenna (LPA) of the Pushchino Radio Astronomy Observatory at 111 MHz in a 2.5-MHz band. The 96-beam directivity pattern of the LPA is used. The signal is received in six 0.42-MHz frequency channels with a sampling rate of 0.1 s. The duration of the processed survey is four months. The particulars of detecting periodic sources with the LPA are considered. In total, 16 such radio sources have been detected, for which equatorial and Galactic coordinates, periods, and dispersion measures are given.

The results of ultra‐rapid flux fluctuations monitoring in 2002–2009 for galactic sources of water‐vapor maser emission at a wavelength of 1.35 cm

Results of a search for ultra rapid flux fluctuations of galactic sources of maser emission in the water‐vapor line at a wavelength of 1.35 cm. An observational technique of a search for ultra rapid flux fluctuations has been developed. From 2002 to 2009 a number of observational sessions for about 40 maser sources have been carried out. Several of them have demonstrated such a variability. Possible mechanisms of the variability are discussed, among them internal processes within the sources themselves as well as external ones, including the theoretical possibility of a resonant effect of gravitational waves from galactic objects on the maser region. Clear evidence for the presence of such a variability has been found in several sources (Cep A, W43M3, W49N, W33B). This variability appears not permanently, but only certain states of particular H2O masers. In some sources (Ori A, W3 OH, W49N) demonstrated any variations by linear polarization of signal.

Twenty-six-year monitoring of water masers

Since 1980 variability of a sample of H 2 O maser sources has been monitored on the 22-metre radio telescope in Pushchino, Russia. The interval between successive observational sessions is 1–2 months. The sample includes 125 maser sources in star-forming regions (SFR) and late-type variable stars. Twenty-six-year time series of H 2 O line profiles have detected flares and velocity drift of spectral features. Very fast variations in the H 2 O maser flux (Δ t ≲ 1 hour) have been detected in several SFR sources, in particular, W33B. Variations of circumstellar H 2 O masers in late-type stars correlate with visual light curves with a time lag of 0.3-0.4 P ( P is the stars period). Exceptionally strong H 2 O maser flares were recorded in SFR sources (Sgr B2 and others) and in the stars W Hya, R Cas and U Ori. Models for H 2 O maser variability are reviewed. For stellar masers shock-wave excitation of H 2 O line variability is discussed.

Water masers in red supergiants

Results of long-term monitoring of circumstellar water maser sources in red supergiants are reviewed. The observations were carried out in 1980–2006 on the RT-22 radio telescope at Pushchino Radio Astronomy Observatory. We discuss the results for the semiregular variable M-supergiant VX Sgr and non-variable M-supergiant IRC–10414. In addition to our single-dish data, very-long-baseline interferometry results are invoked. VX Sgr and IRC–10414 display a characteristic water line profile, which suggests the presence of a rotating circumstellar disc and a bipolar outflow.

MERLIN and Puschino Observations of H2O Masers in Outer Galactic SFR S128N

We have imaged H2O maser emission from the star-forming region S128 at milli-arcsec resolution using MERLIN, to complement 20 years of monitoring data from the Puschino radio telescope. The drift velocities of the masers and the velocity and location of a new maser region add depth to the model of two colliding CO clouds triggering collapse. Some H2O masers appear to originate directly from this shock front. The brightest maser appears typical of a YSO jet and remains unsaturated close to peak intensity. The distribution of maser clumps has a fractal dimension ∼0.4; combined with analysis of drift velocity variations this suggests that the masers trace the dissipation of supersonic turbulence. The spatial distribution of velocities shows that this is in parts more structured than the Kolmogorov cascade.

Analysis of time series in space maser signals

Many astrophysical sources that emit narrow radio-frequency spectral lines are believed to be sets of molecular condensation, each of which works as a maser, so that the whole set produces a characteristic spectrum. The forms of these spectra vary with time on various time-scales from months to dozens of minutes. We analysed the ultra-short variations of the separate components of space maser spectra in search for the periodical behaviour. We used a consecutive statistical analysis of the observation data that includes fast Fourier transformations (FFTs), a Lomb-Scargle procedure, and a modified Lomb-Scargle procedure. In at least 8 of the 49 sources we studied, we found that the intensity of one of the components of a space maser spectrum that corresponds to a single condensation changes periodically with a period of dozens of minutes or hours. Three sources had a period of 68 min; in one source the oscillations lasted at least four days.

The database of observational results at PRAO ASC LPI sites and on‐line pre‐processing of the data by their monitoring in the database

The site ”Electronic database of observation results from radio telescopes of PRAO ASC LPI” (http://observations.prao.ru/) was launched in 2006. This database provides access to observational instruments and telescope descriptions, techniques of making data samples per instruments, information about types of observations, observers and dates of observations and so on. As of August 2009, the observational result database contained more than 126000 data files. Data from PRAO instruments and radio telescopes are continuously being stored to this database. The statistical analysis of the data and its pre‐processing facilities are available on‐line from this database. Facilities for graphical display information and statistical analysis of data of some kinds of celestial radio sources were added to this system, and work on widening of sampling this sources with the aim of accounting every kinds of radio sources is carried out. The development of new facilities for on‐line processing of monitoring data from PRA...