A second set of RATAN-600 observations of giant radio galaxies

Results of RATAN-600 centimeter-wavelength flux-density measurements of the extended components in five giant radio galaxies are reported. The spectra of the components of these radio galaxies have been constructed using the data of the WENSS, NVSS, and GB6 surveys together with new RATAN-600 data. Spectral indices in the studied frequency range have been calculated.     

Objects from a cross-identification of the IRAS and low-frequency Texas radio catalogs

A cross-identification of objects in the low-frequency (365 MHz) Texas radio catalog and in IRAS catalogs at four infrared wavelengths has yielded a list of 715 objects for further studies. Objects with steep spectra for which the difference in the centers of gravity of the radio and infrared sources was less than 3″ were selected from this list. Seventeen of the objects have been observed at six wavelengths using the RATAN-600 radio telescope. Spectra of nine objects from the initial list for which there were candidate optical counterparts were obtained using the 2.1-m telescope of the INAOE. The results of these observations are discussed. The presence of steep spectral indices for the radio sources is confirmed. The possible optical counterparts include interacting galaxies, an infrared galaxy, two emission-line galaxies, and a candidate BL Lac object. Optical images of the optical counterparts are presented together with radio and optical spectra.     

Radio and optical spectral studies of radio sources

Optical identifications and an analysis of the radio spectra of eight radio sources from a flux-density-complete sample at declinations 4°–6° (B 1950) are presented. The observations were carried out at 4000–9000 Å on the 6-m telescope of the Special Astrophysical Observatory and at 0.97–21.7 GHz on the RATAN-600 telescope. Five of the eight sources are quasars and three are emission-line radio galaxies.     

The active galaxy NGC 3862 in a compact group in the cluster A1367

We study a compact group of 18 galaxies in the cluster A1367 with redshifts z = 0.0208–0.025. The group’s center of activity in the radio is the galaxy NGC 3862, whose radio flux is an order of magnitude stronger than for the other members of the group. We present coordinates derived from the Palomar plate archive together with recessional velocities, and analyze other characteristics of the group’s galaxies. The results of 1400 MHz observations of NGC 3862 with the RATAN-600 radio telescope are presented. These observations indicate that the galaxy’s radio emission is variable.     

Radio spectra of objects in the RATAN-600 RZF catalog and a population analysis of faint radio sources

Results of centimeter-wavelength RATAN-600 observations of several hundred NVSS objects with a wide range of flux densities are presented. Changes in spectral-index distributions from strong-to faint-object populations are estimated. In the transition from strong to faint radio sources, the number of steep-and ultrasteep-spectrum objects decreases and the minimum between steep-and flat-spectrum objects, which was first discovered in the 1970s, becomes less distinct. A less certain increase in the fraction of inverted-spectrum objects is also found. Comparison with theoretical models of radio-source evolution suggests that the decrease in the number of steep-and ultrasteep-spectrum objects can be naturally explained by a sharp decrease in the fraction of classical FRII radio galaxies. The decrease in the sharpness of the minimum may be due to the growing contribution from the population with spectral indices 0.7–0.5, which is usually identified with starbust galaxies. The small increase in the fraction of inverted-spectrum radio sources can be attributed to the growing number of objects with active nuclei. Our spectrum-based conclusions are confirmed by the morphology of the FIRST Catalog images. The number of radio sources associated with supermassive black holes in the Early Universe is estimated using data from the SDSS Catalog.     

Spectrum of the variable component of the radio source J0157+7442

The spectrum of the maximum values of the variable component of the radio source J0157+7442 is presented. The flux densities obtained on the RATAN-600 radio telescope at centimeter wavelengths in 2009 and 2010 are minimum for all observations of the source, and it was assumed that the variable component was absent in these years. After subtracting these RATAN-600 data from the upper envelope of all available flux density data, the spectrum of the variable component was obtained. The form of the spectrum of the variable component is typical of a nonuniform, spherically symmetric source with synchrotron self-absorption.     

Statistical radio astronomy of the 21st century

The exponential development of radio-astronomy methods (sensitivity, resolution, depth of surveys, etc) has led to the need for new methods aimed at distinguishing weak signals in the midst of numerous background signals, as has long been the case for radio astronomy at meter wavelengths. Centimeter-wavelength data accumulated with existing radio telescopes (such as the RATAN-600 reflector—the largest radio telescope in Russia) are presented, and expected problems for major new radio telescopes of the 21st century, such as the Square Kilometer Array, are discussed. The effectiveness of using certain tested methods to derive astrophysically important results through reasonable statistical processing of large datasets is shown. In experiments conducted with RATAN-600, these methods lead to an enhancement in sensitivity by an order of magnitude compared with the sensitivity of a resolving element.     

Radio and optical spectra of objects from two complete samples of radio sources

We present optical identifications and radio spectra for ten radio sources from two flux-density-complete samples. Radio variability characteristics are presented for four objects. The observations were obtained on the RATAN-600 radio telescope at 0.97–21.7 GHz and the 2.1 m telescope of the Haro Observatory in Cananea, Mexico at 4200–9000 Å. Among the ten objects studied, three are quasars, four are BL Lac objects, two are radio galaxies, and one is a Sy 1 galaxy. Two of the sources identified with BL Lac objects, 0509+0541 and 0527+0331, show rapid variability on time scales of 7–50 days.     

Spectral studies with the Special Astrophysical Observatory 6 m and RATAN-600 telescopes

We present optical identifications, classifications, and radio spectra for 19 radio sources from a complete sample in flux density with declinations 10°–12°30′ (J2000) obtained with the 6-m optical telescope (4000–9000 Å) and RATAN-600 radio telescope (0.97–21.7 GHz) of the Special Astrophysical Observatory. Twelve objects with redshifts from 0.573 to 2.694 have been classiffied as quasars, and two objects with featureless spectra as BL Lac objects. Four objects are emission-line radio galaxies with redshifts from 0.204 to 0.311 (one also displaying absorption lines), and one object is an absorption-line galaxy with a redshift of 0.214. Radio flux densities have been obtained at six frequencies for all the sources except for two extended objects. The radio spectra of five of the sources can be separated into extended and compact components. Three objects display substantial rapid (on time scales from several days to several weeks) and long-term variability of their flux densities.     

RATAN-600 surveys and the cosmological gene of the universe

Historical aspects of sky surveys carried out on the RATAN-600 radio telescope and studies of radio sources and background radiation detected in these surveys are considered.     

Detection of a cyclotron line in the radio spectrum of a solar active region and its interpretation

Observations of the active region AR 7962 obtained at 2–32 cm on the RATAN-600 radio telescope on May 10–12, 1996, are presented. The high-resolution measurements detected a narrow feature near 8.5 cm against the background of the smooth spectrum of the local source associated with sunspots. This narrow-band emission is identified with a bright, pointlike, high-frequency source at 1.7 cm recorded on maps made using the Nobeyama radio telescope. The characteristics of the observed line (lifetime 3 days, brightness temperature of the order of several million Kelvin, relative width of about 10%) suggest that it can be explained as thermal cyclotron radiation at the third harmonic of the electron gyrofrequency from a compact source containing a dense, hot plasma; the corresponding higher frequency emission could be due to thermal Bremsstrahlung. Analysis of the RATAN-600 and Nobeyama data can be used to probe the magnetic field, kinetic temperature, and electron density in the radiation source in the corona.     

Variability of the radio flux density of the Blazar S5 0716+714 on time scales less than a month

Results of a study of the variability of the BL Lac object S5 0716+714 are reported. The data were obtained in 150 daily observations on the RATAN-600 radio telescope at six frequencies from 0.97 to 21.7 GHz and 13 day-long sessions at a wavelength of 6.2 cm on the 32 m radio telescopes of the Zelenchukskaya, Svetloe, and Badary observatories (Quasar-KVO complex, Institute of Applied Astronomy, Russian Academy of Sciences). The RATAN-600 observations detected three “anti-flares,” or eclipses, when the flux density decreased from an initially constant level and then returned to this level. The eclipse time scales obtained from an analysis of light curves, structure functions, and autocorrelation functions are 12–20 days; the eclipse spectra were determined. Intraday variability (IDV) with time scales of 10–12 hours was detected in three sessions on the 32-m radio telescopes.     

The KHOLOD experiment: A search for a new population of radio sources

Published data from long-term observations of a strip of sky at declination ?? ?? 5° carried out at 7.6 cm on the RATAN-600 radio telescope are used to estimate some statistical properties of radio sources. Limits on the sensitivity of the survey due to noise imposed by background sources, which dominates the radiometer sensitivity, are refined. The vast majority of noise due to background sources is associated with known radio sources (for example, from the NVSS with a detection threshold of 2.3 mJy) with normal steep spectra (?? = 0.7?C0.8, S ?? ?? ^??? ), which have also been detected in new deep surveys at decimeter wavelengths. When all such objects are removed from the observational data, this leaves another noise component that is observed to be roughly identical in independent groups of observations. We suggest this represents a new population of radio sources that are not present in known catalogs at the 0.6 mJy level at 7.6 cm. The studied redshift dependence of the number of steep-spectrum objects shows that the sensitivity of our survey is sufficient to detect powerful FRII radio sources at any redshift, right to the epoch of formation of the first galaxies. The inferred new population is most likely associated with low-luminosity objects at redshifts z < 1. In spite of the appearance of new means of carrying out direct studies of distant galaxies, searches for objects with very high redshifts among steep and ultra-steep spectrum radio sources remains an effective method for studying the early Universe.     

Quasi-simultaneous VLBI and RATAN-600 observations of active galactic nuclei

VLBI observations of several quasars and BL Lacertae objects were carried out at 1.66 GHz in November–December 1999 using six antennas (Medvezh'i Ozera, Svetloe, Pushchino, Noto, HartRAO, and Shanghai). Maps of six sources (0420+022, 0420-014, 1308+326, 1345+125, 1803+784, and DA 193) obtained with milliarcsecond resolution are presented and discussed, together with their broad-band (1–22 GHz) spectra obtained on the RATAN-600 radio telescope at epochs close to those of the VLBI observations. Comparison of the VLBI maps with maps of these sources obtained on standard VLBI networks and with the RATAN-600 quasisimultaneous total-flux measurements indicates the reliability of the results obtained on this Low Frequency VLBI Network and the good efficiency of this network.     

Radio Sources in the Central Section of the RZF Catalog. Search for Objects with Ultra-Steep Spectra

Results of reducing and selecting data from the Ratan Zenith Field (RZF) are presented. A deep survey in the region 0^h ≤ R.A. ≤ 24^h, 40.5° ≤ DEC ≤ 42.5° carried out on the RATAN-600 radio telescope was used. Within +2′ of the center of the survey region, 448 objects were detected, 69 of them with ultra-steep spectra (USS). The SDSS digital optical survey (DR12), NVSS radio maps, and the FIRST catalogs have been used to cross-identify 208 radio sources from the RZF catalog, obtained as part of the “Genetic Code of the Universe” project. The characteristics of these objects are studied, and the distribution of the SDSS galaxies in a two-color diagram is obtained. Photometric redshifts and radio luminosities at 3940 and 1400 MHz are determined for 27 objects with spectral indices α < −1.1 (S ∝ ν^α) for which magnitudes in various filters are presented in the SDSS. In the sample of USS objects, 12 galaxies have redshifts z < 0.5, are detected at wavelength λ = 7.6 cm, and have relatively high radio luminosities (type FR II or intermediate type FR I–FR II). Only one radio galaxy proved to be a rare nearby galaxy with relatively low radio luminosity L_{1400 MHz} = 1.51 × 10²⁴ W/Hz (type FR I). Two objects are candidate GHz-Peaked Spectrum objects.

     

Classification of optical identifications of radio sources from complete samples

Classifications of the optical counterparts and radio spectra of nine radio sources are presented. The observations were carried out using the 2.1-m optical telescope in Cananea (Mexico) at 4200–9000 Å and the RATAN-600 radio telescope at 0.97–21.7 GHz. Five objects have been classified as quasars (three have redshifts z>2), two as BL Lac objects, one as an elliptical galaxy, and one as an absorption-line galaxy.     

Physics of post-eruptive solar arcades: Interpretation of RATAN-600 and STEREO spacecraft observations

Results of simultaneous measurements of radiation fluxes from post-eruption arcades on the Sun at 171, 195, 284, and 304 ? (from STEREO spacecraft data) and at radio wavelengths (from the RATAN-600 radio telescope) are presented. An original probabilistic approach developed earlier by Urnov was used to determine the differential emission measure. This method requires no regularization, and the obtained results do not depend on the choice of the temperature grid. This approach has yielded the differential measure of emission at temperatures approximately from 0.3 to 15 MK. The subsequent calculation of thermal magnetobremsstrahlung in a multi-temperature model with the magnetic field decreasing with height produces a spectrum similar to that observed on RATAN-600. Thus, in many non-stationary events with modest powers, a thermal multi-temperature model is quite able to explain the emission of post-eruption arcade systems, and it is not necessary to invoke the emission of accelerated particles. The proposed model enables direct estimation of the ratio of the magnetic and gas pressures at the tops of post-eruption arcades, and determination of the conditions required for the origin of secondary nonstationary processes in the decay stage of the main flare.     

Spectra,optical identifications,and statistics of a complete sample of radio sources at declinations 10°–12°30′

The results of 0.97, 2.3, 3.9, 7.7, 11.1, and 21.7 GHz observations of a complete sample of radio sources obtained on the RATAN-600 radio telescope are presented. The sample is comprised of sources from the 4.85-GHz MGB survey, and contains all sources at declinations 10°–12°30′ (J2000) with Galactic latitudes |b|>15° and flux densities S_4.85>200 mJy. Optical identifications have been obtained for about 86% of the radio sources with flat spectra and 59% of those with steep spectra. The spectra of the flat-spectrum sources have been decomposed into extended and compact components.     

Variability of the flux densities of radio sources on timescales shorter than a month

Results of a study of the variability of radio sources on timescales of 3–30 days based on six sets of daily observations on the RATAN-600 radio telescope with durations from 53 to 103 days at six frequencies from 0.97 to 21.7 GHz are reported. The variability timescales and spectra determined from the analysis of light curves, structure functions, and autocorrelation functions for 11 radio sources from a complete sample in the declination range 4°–6° (B1950) are presented.     

Optical identifications and spectra of radio sources

We present classifications, optical identifications, and radio spectra for eight radio sources from three flux-density-complete samples in the following declination ranges: 4°–6° (B1950), S _3.9 > 200 mJy; 10°–12°30′ (J2000), S _4.85 > 200 mJy; 74°?75° (J2000), S _4.85 > 100 mJy. For all these samples, the right ascensions are 0^h–24^h and the Galactic latitudes, |b| > 15°. Our optical observations at 4000–7500 ° were made with the 6-m telescope of the Special Astrophysical Observatory; we also observed at 0.97–21.7 GHz with the RATAN-600 radio telescope of the Special Astrophysical Observatory. We classify four of the objects as quasars and four as galaxies. Five of the radio sources have power-law spectra at 0.97–21.7 GHz, while two objects have flat spectra. The quasar J2358+0430 virtually did not vary during 23 years.