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.     

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

We present classifications, optical identifications, and radio spectra for 19 radio sources from three complete samples, with declinations 4°–6° (B1950, S _{3.9 GHz} > 200 mJy), 10°–12°30′ (J2000, S _{4.85 GHz} > 200 mJy), and 74°–75° (J2000, S _{4.85 GHz} > 100 mJy). We also present corresponding information for the radio source J0527+0331. The right ascensions are 0–24^h and the Galactic latitudes |b| > 15° for all the samples. Our observations were obtained with the 6 m telescope from the Special Astrophysical Observatory in the range 4000–9000 Å or 4000–7500 Å and the RATAN-600 radio telescope at frequencies in the range 0.97–21.7 GHz. We obtained flux densities for the radio sources and optical spectra for their optical counterparts. Nine objects were classified as quasars with redshifts from z = 1.029 to 3.212; nine objects are emission-line galaxies with redshifts from 0.172 to 0.546, and one is a galaxy with burstlike star formation at z = 0.156, and one is a BL Lac object with z = 0.509. The spectra of five radio sources were decomposed into extended and compact components. The radio source J0527+0331, identified with a BL Lac object, displays significant variations of time scales from several days to several years. Data on flux variations are presented for 11 radio sources, as well as their spectra at several epochs.     

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.     

Flux density variability of radio sources at declinations 10°–12°30′ (J2000) on time scales less than a month

Results of a search for and study of variability in a complete sample of flat-spectrum radio sources (83 objects) on time scales longer than a day are reported. The data were obtained in six series of daily observations on the RATAN-600 radio telescope made over 77–103 days at six frequencies from 0.97 to 21.7 GHz and at declinations of 10°–12°30′ (J2000). Variability on time scales of 3–30 days with significance levels below 1% was detected for 19 sources. The time scales, modulation indices, and spectra of the variability derived from an analysis of the light curves, structure functions, and autocorrelation functions are presented for these sources. For a number of them, intrinsic variability and extrinsic variability due to scintillations in the turbulent interstellar medium have been separated. The obtained source characteristics are compared with those for sources at declinations 4°–6° (B1950).     

Instantaneous spectra for a complete sample of radio sources in the declination range 74°–75°

We present the results of observations of a complete sample of radio sources with the RATAN-600 radio telescope at 0.97, 2.3, 3.9, 7.7, 11.1, and 21.7 GHz. The sample was extracted from the GB6 catalog at 4.85 GHz, and contains all the sources at declinations 74°–75° (J2000) with flux densities S _4.85 > 100 mJy. We have obtained optical identifications for 67% of the radio sources with flat spectra and 30% of those with steep spectra.     

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.     

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.     

Spectral characteristics and variability of radio sources near the north celestial pole

We present the results of our observations of compact extragalactic radio sources near the north celestial pole (+75° ≤ δ ≤ +88°) obtained on the RATAN-600 radio telescope. Our sample consists of 51 radio sources with spectra that are either flat or inverted (growing toward shorter wavelengths) and with flux densities at 1.4 GHz S _ν ≥ 200 mJy. We observed the sources at 1–21.7 GHz. Multi-frequency instantaneous spectra are presented for 1999–2007. We observed 33 of our sample source daily for 30 days in August 2007. As a result, we revealed 15 objects exhibiting rapid variations on time scales of a day. The multi-frequency instantaneous spectra of these sources indicate that radio flux variations on one-day timescales are characteristic of objects of various spectral types. More than half the sources exhibiting rapid variations demonstrate a growth in the variability amplitude with increasing frequency. For some of the objects, the variability amplitude is virtually independent of frequency.     

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.     

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.     

Candidate GPS sources near the North Celestial Pole

Results of observations of the five candidate GPS sources J0626+8202, J0726+7911, J1044+8054, J1823+7938, and J1935+8130 are presented. GPS sources are extragalactic sources whose spectral peaks are near several GHz. These objects were observed on the RATAN-600 radio telescope from 1999 through 2010 at 1.1, 2.3, 4.8, 7.7, 11.2, and 21.7 GHz. These radio sources were selected from a complete sample (S _v ≥ 200 mJy at 1.4 GHz) in the vicinity of the North Celestial Pole (+75° ≤ δ ≤ +88°); four are considered as GPS candidates for the first time here. Their spectral properties, variability and morphology are analyzed, and confirms that these can be classified as GPS sources. These four to five GPS sources probably comprise a complete sample of this class of object in this region of the celestial sphere.     

Monitoring of flux densities of bright radio sources in a narrow strip of sky at 1420 MHz

The flux densities of a uniform sample of extragalactic radio sources in a narrow strip of sky (1° wide in declination with a total area of about 0.1 sr) were monitored for 105 days at 1420 MHz using the 64-m Kalyazin radio telescope. In total, 32 bright sources with flux densities greater than 0.6 Jy have been studied. The statistical properties of the observed flux-density variations are discussed. We detected variability at the 95% confidence level according to the χ ² test in 4C +27.15 (0516+2740). The flux density variations in this source show the pattern typical of extreme scattering events. There are reasons to classify this source as a blazar.     

Analysis of instantaneous spectra of a complete sample of flat-spectrum radio sources

The results of observations of a complete sample of radio sources with spectral indices α>?0.5 (S∝v ^α) are presented. The sample was selected from the Zelenchuk Survey at 3.9 GHz and contains all sources with declinations 4°–6°, Galactic latitudes |b|>10°, and 3.9-GHz fluxes >200 mJy. Spectra at 0.97–21.7 GHz were obtained for all 69 sample sources. The spectra were classified, and a correlation between variability amplitude and spectrum shape was found. The spectra were separated into extended and compact components. The distribution of spectral indices α for the extended components coincides with the distribution for sources with power-law spectra. The correlation between the luminosity and frequency of the peak flux density is confirmed. This correlation is due to the fact that the distribution of source linear dimensions does not depend on luminosity.     

Detection of prolonged, extremely faint decimeter bursts on the sun

We report the detection of long-lived sources of radio bursts accompanied by polarized background emission in solar active regions. Both types of radio sources were detected at several decimeter wavelengths in observations on the RATAN-600 radio telescope in one-dimensional scans in intensity and circular polarization with a sensitivity of about 5–10 Jy. The degree of polarization is from 70 to 100%. The microburst and background sources exist for several days and appear at sites of prolonged energy release. The typical duration of an individual microburst is about 1–2 s, and the time interval between microbursts is about 3–5 s. A negative microburst frequency drift of about 100 MHz/s or more is also observed. Some interpretations of the microburst and background sources are discussed. The most probable microburst model involves the generation of radio emission via the plasma mechanism, with the upward propagation of fast electrons above an active region. In this case, the required energy of the Langmuir waves is 2×10^?8 of the heat energy of the background plasma. Microbursts appear in different places in an active region. New methods for determining the magnetic-field intensity in the regions of generation of the decimeter-wavelength emission are proposed.     

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.     

Long-term variability of a complete sample of flat-spectrum radio sources at declinations 10°–12°30′ (J2000)

The paper reports the results of ten-year centimeter-wavelength observations with the RATAN-600 radio telescope of a complete sample of 83 flat-spectrum sources from the GB6 catalog of the MGB Survey, with S _4.85 > 200 mJy at declinations 10°?C12°30??. Starting in 2000, the observations were conducted simultaneously at six frequencies in the range 0.97?C21.7 GHz. Seventy-six sources (including 54 quasars) have been identified with optical objects, which have redshifts in the range z = 0.331?C3.601. Analysis of light curves and spectra at different activity phases has shown that, in most cases, the dynamics of the development of flares is consistent with a model in which the variability results from the evolution of a shock in a radio jet. A relationship between the time scales for the rise and fall of the flares has been found. There is no redshift dependence of the true linear dimensions of the radiating regions and the variability indices obtained over ten years. These facts can be interpreted as an absence of cosmological evolution of quasars at least up to z ?? 3.     

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.

     

Compact radio sources and interstellar scattering near the galactic center

Using literature data on approximately 400 compact radio sources detected with the Very Large Array and located in the direction of the Galactic center within 2° of the compact source Sgr A*, 69 sources whose angular sizes are determined by scattering on electron density inhomogeneities were distinguished. Fifty-five of these are extragalactic, two are supercompact HII regions, ten are sources of maser emission, and two are variable Galactic sources. The excess of the apparent angular sizes of maser sources within 2° of the Galactic center above the mean size of objects of this class in other parts of the Galaxy found in many studies cannot be explained purely by the effect of scattering of their radio emission on interstellar plasma inhomogeneities. The angular sizes of these objects are increased due to scattering only within Galactic longitudes of about 0.4° and Galactic latitudes less than 0.1°. The turbulent medium responsible for scattering of radio emission of compact sources in the immediate vicinity of the Galactic center is strongly concentrated toward the compact source Sgr A* at the Galactic center. No extragalactic sources are observed within 0.4° in longitude and 0.2° in latitude of the Galactic center, because of their low brightness due to the superstrong scattering in this region. Data on scatter broadening can be used to study the distribution of turbulent plasma near the Galactic center.     

Mapping of bipolar outflows and methanol masers in the CS(2-1)line

Eighteen regions (bipolar outflows and methanol masers) are mapped in the CS(2-1) line using the 20-m Onsala radio telescope. The coordinates of the CS emission peaks are refined. The sizes and masses of dense regions are estimated for 13 maps. Measurement of the angular sizes of regions of emission indicates that all the sources were resolved by the Onsala radio telescope. The lower limit for the linear dimensions of the CS condensations studied is 0.2–2.1 pc. The hydrogen densities and masses of the CS condensations are estimated to be n(H₂)=(0.3–13.1)×10⁴ cm^?3 and (M ≈ 7–2800M _⊙). Methanol masers are associated with denser and more massive regions, whether or not the maser condensation is connected with a bipolar outflow.     

Deep surveys and the nonthermal noise of radio telescopes

The paper presents an analysis of catalogs of discrete radio sources and the results of deep surveys carried out with angular resolutions to 1.5″ and limiting flux densities to 9 μJy at frequencies from 80 MHz to 8.5 GHz using large radio telescopes around the world. We consider the influence on the sensitivity of a radio telescope of the nonthermal noise associated with variations in the total flux due to fluctuations in the number of unresolved sources with fluxes lower than the observed value that fall in the main lobe of the antenna beam when the direction in which the receiver is pointed is changed (the first component), and also due to sources with fluxes higher than the observed value that arrive in the scattering region of the telescope (the second component). With growth in the sensitivity and resolution of a telescope, the second component of this nonthermal noise determines to an appreciable extent the limiting capability of the telescope for carrying out deep surveys. We estimate the number of antenna beams per source that are required to reach a specified sensitivity in deep surveys. The results of our calculations are compared with data derived from catalogs and numerous surveys.