Yu. V. Sotnikova

Spectral characteristics of radio sources near the North Celestial Pole

We have used the RATAN-600 radio telescope to study the spectral characteristics of a uniform sample of 504 radio sources from the NVSS catalog near the North Celestial Pole at six frequencies from 1.1 to 21.7 GHz, with the aim of selecting sources possessing inverted spectra near 22 GHz, to be included in the program of the Radio Astron future space VLBI mission. We found 17 radio sources with the desired spectral characteristics. Data from spectral studies over a wide wavelength range testify that the spectral behavior of our sample differs from that for a complete sample of sources with the same initial parameters but selected at 20 GHz. We find a 6% deficit of inverted-spectrum sources, which can be explained as an effect of the spectral characteristics of “sub-threshold” sources that were not included in the initial sample at 1.4 GHz.

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 Sν ≥ 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.

Observations of the rapid variability of the two BL Lac type objects J2005+77 and J2022+76 with the RATAN-600

We report here the results of observations of two BL Lacertae-type objects, J2005+77 and J2022+76, using the RATAN-600 at frequencies 11.2, 7.7, and 4.8 GHz. We found variations of radio emission on timescales of one day and we are the first to discover a variability of this type for J2022+76.We compare our observations with long-term multifrequency radio observations of the same sources performed on RATAN-600 within the framework of other observational programs. We analyze the behaviour of variability of the two sources and provide arguments in favour of the preferred emission generation mechanisms for the objects studied.

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 (Sv ≥ 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.

Gigahertz-peaked spectrum (GPS) galaxies and quasars

The results of a comprehensive analysis of continuous radio spectra of a sample of Gigahertz-Peaked Spectrum (GPS) sources are reported. The sources are selected from a flux-density-complete sample (Sν ≥ 200 mJy at 4.8 or 5 GHz) using multifrequency measurements of the RATAN-600 radio telescope and data from the CATS astrophysical catalogs support system. The analysis revealed a very small number (1–2%) of “classical” GPS objects, which is significantly less than the expected fraction of 10%. GPS galaxies are found to have narrower and steeper radio spectra than quasars. The low-frequency part of the spectrum is seen to become steeper with increasing redshift. Galaxies and quasars at the same z have comparable angular sizes, whereas their luminosities may differ by one order of magnitude. At large redshifts there is a deficit of objects with low (several GHZ) peak frequencies. The number of GPS galaxies decreases sharply with redshift, and most of them are found at z between 0.01 and 1.81. GPS quasars are found at large redshifts, from 0.11 to 3.99. A quarter of the sample consists of blazars whose spectra may temporarily have a convex shape when the object is in active state.

Automated system for reduction of observational data on RATAN-600 radio telescope

We present the automated systemfor estimating the parameters of radio sources observed on all available continuum radiometers (two receiving facilities of secondary mirrors No. 1 and No. 2 with a total of 30 radiometers) developed at RATAN-600 radio telescope and put into normal operation. The system is also used for the monitoring of the parameters of the antenna and receiving systems of RATAN-600 radio telescope, which is carried out using current measurements of calibration radio sources.

A study of the synchrotron component in the blazar spectral energy distributions

We study the synchrotron component of nonthermal radiation of blazars using the spectral energy distribution (SED). The sample contains a total of 877 blazars, including 423 flat-spectrum radio quasars (FSRQs), 361 BL Lac objects and candidates, and 93 blazars of uncertain type. Using the ASDC SED Builder Tool, we have made an estimation of the synchrotron peak frequency νpeaks using archive data of different catalogs. The position of the synchrotron peak frequency was determined for 875 objects, which were further classified as follows: 611 low-synchrotron peaked (LSP) blazars (νpeaks < 1014.5 Hz), 222 intermediate-synchrotron peaked (ISP) blazars (1014.5 < νpeaks < 1016.5 Hz), and 42 high-synchrotron peaked (HSP) sources (νpeaks > 1016.5 Hz). For the FSRQs the average νpeaks is 1013.4±1.0 Hz, for the BL Lac-type blazars it equals 1014.6±1.4 Hz. We found that νpeaks values and the spectral flux density at 4.8 GHz form different distributions for two types of blazars—FSRQ and BL Lac— and for the radio-selected (RBLs) and x-ray-selected (XBLs) blazars. The distribution of νpeaks values is broader for BL Lac objects than for FSRQs. There are no ultra-high-energy synchrotron-peak BL Lac objects (UHBLs, with νpeaks > 1019 Hz) in our sample. We have found very-low-synchrotron peaked (VLSP) blazar candidates (with νpeaks < 1013 Hz). Most of them are the FSRQs (41% of the total number) and only 9%are the BL Lac objects. Our results confirm the results of other authors, made on the samples with a significantly smaller number of objects.We study the synchrotron component of the spectral energy distribution (SED) on the sample of 877 blazars using the ASDC SED Builder Tool with available broadband data from the literature. Our sample includes 423 flat-spectrum radio sources (FSRQs), 361 BL Lac objects and candidates, and 93 blazars of uncertain type. We have made an estimation of the synchrotron peak frequency (ν peak) for the 875 objects and further classified them as high, intermediate and low synchrotron peaked sources (HSPs/ISPs/LSPs). There are 42 HSPs with ν peak > 10 16.5 Hz, 222 ISPs with

A method of determining the kinematic properties of the primary mirror elements of the RATAN-600 radio telescope using modern laser measuring systems

We review the methods of determining the alignment errors of the primary mirror and flat reflector elements of the RATAN-600 radio telescope using a modern coordinate measuring system based on the Leica absolute tracker AT402. We computed the kinematic corrections for the elevation drives. The accuracy of the measurement method was estimated. The antenna readout with the introduced kinematic corrections was tested.

Multifrequency quasi-simultaneous observations of six low-synchrotron peaked blazars

We made an estimation of the synchrotron peak frequency (νpeaks) of the spectral energy distribution (SED) for six blazars. These objects were selected as very-low-synchrotron peaked (VLSP) blazar candidates (with νpeaks ≤ 1013 Hz).We have built the SED of the studied objects using quasi-simultaneous observations on the SAO RAS Zeiss-1000 and RATAN-600 telescopes and made an estimation of the synchrotron peak frequency. As a result, three sources (PKS0446+11, [HB89] 1308+326, and 3C345) were confirmed as VLSP, for the three remaining blazars the calculations have shown νpeaks > 1013 Hz.

Study of the relation between the jet and accretion-disk emission in Blazars using RATAN-600 multifrequency data

We study the correlation between the emission from the broad-line region (BLR) and the emission in other wavelength ranges (from radio to x-ray) for the sample of 37 blazars (25 flat-spectrum radio quasars (FSRQs) and 10 BLLac blazars). Studying the relation between luminosities in various wavebands and the BLR luminosity is an effective method to examine the connection between the accretion rate and the luminosity of the jet.We used simultaneous RATAN-600measurements of blazar flux densities at six frequencies: 1.1, 2.3, 4.8, 7.7, 11.2, and 21.7 GHz. The observational data from other bands was taken from the literature. To determine the effect produced by the state of the object on the correlation, for the radio data we used the measurements obtained with the RATAN-600 in two states-namely, the maximum and minimum flux density values.We show that at some frequencies of the radio band, there exists a correlation of emission with the emission in the BLR for two types of blazars. In the FSRQ and BL Lac blazars, the correlation between the flux from the BLR and the flux in the radio band is indistinguishable in all cases, except for the case when a strong flux density variation was considered for the BL Lac-type of blazars (tens of percent). At the same time, the levels of significance for BL Lac (at certain frequencies p is worse than 0.05) in the active state indicate only the probable presence of connection. On the example of the sample, we show that the variability of emission significantly affects the level of correlation. Our results are consistent with the theoretical predictions about the close relationship of the accretion disk and the jet in blazars.