arXiv subjects

Yu. A. Kovalev

Publications and source records attributed to Yu. A. Kovalev.

23 records · Page 2Linked to original sources

arXiv2009

Multiwavelength monitoring of the enigmatic Narrow-Line Seyfert 1 PMN J0948+0022 in March-July 2009

Following the recent discovery of gamma rays from the radio-loud narrow-line Seyfert 1 galaxy PMN J0948+0022 (z=0.5846), we started a multiwavelength campaign from radio to gamma rays, which was carried out between the end of March and the beginning of July 2009. The source displayed activity at all the observed wavelengths: a general decreasing trend from optical to gamma-ray frequencies was followed by an increase of radio emission after less than two months from the peak of the gamma-ray emission. The largest flux change, about a factor of about 4, occurred in the X-ray band. The smallest was at ultraviolet and near-infrared frequencies, where the rate of the detected photons dropped by a factor 1.6-1.9. At optical wavelengths, where the sampling rate was the highest, it was possible to observe day-scale variability, with flux variations up to a factor of about 3. The behavior of PMN J0948+0022 observed in this campaign and the calculated power carried out by its jet in the form of protons, electrons, radiation and magnetic field are quite similar to that of blazars, specifically of flat-spectrum radio quasars. These results confirm the idea that radio-loud narrow-line Seyfert 1 galaxies host relativistic jets with power similar to that of average blazars.

astro-ph.HE↗

arXiv2009

On the relation between AGN gamma-ray emission and parsec-scale radio jets

We have compared the radio emission from a sample of parsec-scale AGN jets as measured by the VLBA at 15 GHz, with their associated gamma-ray properties that are reported in the Fermi LAT 3-month bright source list. We find in our radio-selected sample that the gamma-ray photon flux correlates well with the quasi-simultaneously measured compact radio flux density. The LAT-detected jets in our radio-selected complete sample generally have higher compact radio flux densities, and their parsec-scale cores are brighter (i.e., have higher brightness temperature) than the jets in the LAT non-detected objects. This suggests that the jets of bright gamma-ray AGN have preferentially higher Doppler-boosting factors. In addition, AGN jets tend to be found in a more active radio state within several months from LAT-detection of their strong gamma-ray emission. This result becomes more pronounced for confirmed gamma-ray flaring sources. We identify the parsec-scale radio core as a likely location for both the gamma-ray and radio flares, which appear within typical timescales of up to a few months of each other.

astro-ph.GA↗

arXiv2009

A sample of GHz-peaked spectrum sources selected at RATAN-600: spectral and variability properties

We describe a new sample of 226 GPS (GHz-Peaked Spectrum) source candidates selected using simultaneous 1-22 GHz multi-frequency observations with the RATAN-600 radio telescope. Sixty objects in our sample are identified as GPS source candidates for the first time. The candidates were selected on the basis of their broad-band radio spectra only. We discuss the spectral and variability properties of selected objects of different optical classes.

astro-ph.GA↗

arXiv2006

IX Russian-Finnish Symposium on Radio Astronomy "Multi-wavelength investigations of solar and stellar activity and active galactic nuclei"

The IX Russian-Finnish Symposium on Radio Astronomy was held in Special astrophysical observatory RAS in Nizhnij Arkhyz, Russia on 15-20 October 2006. It was dedicated to the two-side collaboration in the field of multi-wavelength investigations of solar radio emission, studies of polar regions of the Sun, studies of stellar activity, AGNs, quasars and BL Lac objects in radio bands from millimeter to decimetre wavelengths with RATAN-600, Metsahovi 14m, RT32m radio telescope and VLBI systems. Here abstracts of all forty papers are given. The Web-site of the Symposium is http://cats.sao.ru/~satr/RFSymp/ .

astro-ph↗

arXiv2004

Survey of Instantaneous 1-22 GHz Spectra of 550 Compact Extragalactic Objects with Declinations from -30deg to +43deg

We present observational results for extragalactic radio sources with milliarcsecond components, obtained with the 600 meter ring radio telescope RATAN-600 from 1st to 22nd December, 1997. For each source, a six frequency broad band radio spectrum was obtained by observing simultaneously with an accuracy up to a minute at 1.4, 2.7, 3.9, 7.7, 13 and 31 cm. The observed list is selected from Preston et al. (1985) VLBI survey and contains all the sources in the declinations between -30deg and +43deg with a correlated flux density exceeding 0.1 Jy at 13 cm. The sample includes the majority of sources to be studied in the current VSOP survey and the future RadioAstron Space VLBI mission.

astro-ph↗