- ID:
- ivo://CDS.VizieR/J/A+A/575/A55
- Title:
- Radio jet emission from GeV-emitting NLSy1
- Short Name:
- J/A+A/575/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the current study we aim at gaining understanding on the properties of radio emission and the assumed jet from four radio loud and {gamma}-ray loud Narrow Line Seyfert 1 galaxies i.e. Seyfert 1 galaxies with emission lines at the low-end of the FWHM distribution. The ultimate goal is twofold; first, the investigation whether a relativistic jet is operating at the source giving out the radio output observed and second, the quantification of the jet characteristics in order to understand possible similarities and differences with the jets found in typical blazars. The current study relies on the most systematic monitoring of radio loud and {gamma}-ray detected Narrow Line Seyfert 1 galaxies in the cm and mm radio bands conducted with the Effelsberg 100-m and IRAM 30-m telescopes. It covers the longest time baselines and the most radio frequencies, to date. This dataset of multi- wavelength, long-term radio light curves is analysed from a number of perspectives. A novel algorithm is introduced in order to extract sensible variability parameters (mainly amplitudes and timescales) which are then used for the computation of variability brightness temperatures and the corresponding Doppler factors. The jet powers are computed from the light curves to estimate the energy output and compare it with typical blazars. The dynamics of radio Spectra Energy Distributions are examined for understanding the mechanism causing the variability. The length of the available light curves for 3 of the 4 sources in the sample allowed a firm understanding of the general behaviour of the sources. They all display intensive variability which seems to be happening at a pace rather faster than what is generally seen in blazars. The flaring events become progressively more prominent as the frequency increases and show intensive spectral evolution indicative of shock evolution. The variability brightness temperatures and the associated Doppler factors are rather moderate implying a mildly relativistic jet. The computed jet powers show very energetic flows. The radio polarisation in one case, clearly implies the presence of a quiescent jet underlying recursive flaring activity. Finally, in one case, the sudden disappearance of a {gamma}-ray flare below some critical frequency in our band, urges for further investigation of the possible mechanism causing the evolution of broadband events. Despite the generally lower flux densities the sources appear to show all typical characteristics seen in blazars powered by relativistic jets. Intensive variability, spectral evolution across the different bands following evolutionary paths explained by traveling shocks, Doppler factors indicating mildly relativistic speeds.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/596/A45
- Title:
- Radio light curves of 8 AGN
- Short Name:
- J/A+A/596/A45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To fully exploit the scientific potential of the Fermi mission for the physics of active galactic nuclei (AGN), we initiated the F-GAMMA programme. Between 2007 and 2015 the F-GAMMA was the prime provider of complementary multi-frequency monitoring in the radio regime. Aims. We quantify the radio variability of {gamma}-ray blazars. We investigate its dependence on source class and examine whether the radio variability is related to the {gamma}-ray loudness. Finally, we assess the validity of a putative correlation between the two bands. Methods. The F-GAMMA performed monthly monitoring of a sample of about 60 sources at up to twelve radio frequencies between 2.64 and 228.39GHz. We perform a time series analysis on the first 2.5-yr data set to obtain variability parameters. A maximum likelihood analysis is used to assess the significance of a correlation between radio and {gamma}-ray fluxes. We present light curves and spectra (coherent within ten days) obtained with the Effelsberg 100m and IRAM 30m telescopes. All sources are variable across all frequency bands with amplitudes increasing with frequency up to rest frame frequencies of around 60-80GHz as expected by shock-in-jet models. Compared to flat-spectrum radio quasars (FSRQs), BL Lacertae objects (BL Lacs) show systematically lower variability amplitudes, brightness temperatures, and Doppler factors at lower frequencies, while the difference vanishes towards higher ones. The time scales appear similar for the two classes. The distribution of spectral indices appears flatter or more inverted at higher frequencies for BL Lacs. Evolving synchrotron self-absorbed components can naturally account for the observed spectral variability. We find that the Fermi-detected sources show larger variability amplitudes, brightness temperatures, and Doppler factors than non-detected ones. Flux densities at 86.2 and 142.3GHz correlate with 1GeV fluxes at a significance level better than 3{sigma}, implying that {gamma} rays are produced very close to the mm-band emission region.
- ID:
- ivo://CDS.VizieR/J/MNRAS/362/9
- Title:
- Radio-loud AGN in SDSS
- Short Name:
- J/MNRAS/362/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of 2712 radio-luminous galaxies is defined from the second data release of the Sloan Digital Sky Survey (SDSS) by cross-comparing the main spectroscopic galaxy sample with two radio surveys: the National Radio Astronomy Observatories (NRAO) Very Large Array (VLA) Sky Survey (NVSS, <VIII/65>) and the Faint Images of the Radio Sky at Twenty centimeters (FIRST, <VIII/71>) survey. The comparison is carried out in a multistage process and makes optimal use of both radio surveys by exploiting the sensitivity of the NVSS to extended and multicomponent radio sources in addition to the high angular resolution of the FIRST images. A radio source sample with 95 per cent completeness and 98.9% reliability is achieved, far better than would be possible for this sample if only one of the surveys was used. The radio source sample is then divided into two classes: radio-loud active galactic nuclei (AGN) and galaxies in which the radio emission is dominated by star formation. The division is based on the location of a galaxy in the plane of 4000{AA} break strength versus radio luminosity per unit stellar mass and provides a sample of 2215 radio-loud AGN and 497 star-forming galaxies brighter than 5mJy at 1.4GHz. A full catalogue of positions and radio properties is provided for these sources.
- ID:
- ivo://CDS.VizieR/J/MNRAS/460/3202
- Title:
- Radio-loud AGN with relativistic jets
- Short Name:
- J/MNRAS/460/3202
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep near-infrared (NIR) images of a sample of 19 intermediate-redshift (0.3<z<1.0) radio-loud active galactic nuclei (AGN) with powerful relativistic jets (L_1.4GHz_>10^27^W/Hz), previously classified as flat-spectrum radio quasars. We also compile host galaxy and nuclear magnitudes for blazars from literature. The combined sample (this work and compilation) contains 100 radio-loud AGN with host galaxy detections and a broad range of radio luminosities L_1.4GHz_~10^23.7^-10^28.3^W/Hz, allowing us to divide our sample into high-luminosity blazars (HLBs) and low-luminosity blazars (LLBs). The host galaxies of our sample are bright and seem to follow the {mu}_e_-Reff relation for ellipticals and bulges. The two populations of blazars show different behaviours in the M_K,nuclear_-M_K,bulge_ plane, where a statistically significant correlation is observed for HLBs. Although it may be affected by selection effects, this correlation suggests a close coupling between the accretion mode of the central supermassive black hole and its host galaxy, which could be interpreted in terms of AGN feedback. Our findings are consistent with semi-analytical models where low-luminosity AGN emit the bulk of their energy in the form of radio jets, producing a strong feedback mechanism, and high-luminosity AGN are affected by galaxy mergers and interactions, which provide a common supply of cold gas to feed both nuclear activity and star formation episodes.
- ID:
- ivo://CDS.VizieR/J/PASJ/73/313
- Title:
- Radio loudness and classification for radio source
- Short Name:
- J/PASJ/73/313
- Date:
- 03 Dec 2021 00:54:37
- Publisher:
- CDS
- Description:
- The extragalactic radio sources are divided into two subclasses (radio-loud and radio-quiet sources) in the literature using radio loudness (R), which is defined as the ratio of radio emission to optical emission, but the boundary R-value separating the two classes is different in various sources. In this work, a sample of 2419 objects from the 13th catalog of quasars and active nuclei is used to build a boundary for the two subclasses. To do so, we compiled the radio and optical data, calculated their radio and optical indexes, made K-correction, obtained the radio loudness, and adopted a Bayesian analysis method to the logarithm of radio loudness for classification. We also investigated the correlations of radio loudness with radio/optical luminosities. Our main conclusions are summarized as follows: (1) The distribution of the logarithm of radio loudness (log R) is bimodal, the sources with log R<1.26 are classified as radio-quiet sources, and those with log R>1.26 are classified as radio-loud ones from the Bayesian analysis method. (2) The average radio-optical effective spectral index of radio-quiet sources is <RO>=0.05, while that of radio-loud sources is <{alpha}_RO_>=0.55. (3) There are positive correlations between radio luminosity and radio loudness for both radio-loud sources and radio-quiet sources. (4) A dividing line of separating the distribution of the clusters on the diagram of radio loudness against radio luminosity was obtained statistically to set the boundary between radio-loud sources and radio-quiet sources, with an accuracy of 99.73% based on the classification result from the Bayesian analysis method.
- ID:
- ivo://CDS.VizieR/J/ApJ/658/815
- Title:
- Radio loudness of active galactic nuclei
- Short Name:
- J/ApJ/658/815
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate how the total radio luminosity of AGN-powered radio sources depends on their accretion luminosity and the central black hole mass. Our studies cover about 7 orders of magnitude in accretion luminosity (expressed in Eddington units, i.e., as Eddington ratios) and the full range of AGN black hole masses.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A92
- Title:
- Radio-loud NLSy1 galaxies optical polarisation
- Short Name:
- J/A+A/618/A92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We quantify the temporal behaviour of the optical polarisation fraction and angle for a selected sample of radio-loud NLSy1s. We also search for rotations of the polarisation plane similar to those commonly observed in blazars. The dataset was obtained with the RoboPol polarimeter of the Skinakas observatory as well as the KANATA, Perkins, and Steward observatories. We carried out numerical simulations to assess the probability that long rotations of the polarisation plane were caused by intrinsically evolving electric vector position angles (EVPAs) instead of observational noise. We conclude that it is much more likely that intrinsic rotations are responsible for the observed phenomenology.
- ID:
- ivo://CDS.VizieR/J/AJ/133/1331
- Title:
- Radio observation of HDFS at 2.5, 5.2, and 8.7GHz
- Short Name:
- J/AJ/133/1331
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Deep radio observations of a wide region centered on the Hubble Deep Field-South have been performed, providing one of the most sensitive sets of radio observations acquired on the Australia Telescope Compact Array to date. A central rms of ~10uJy is reached at four frequencies (1.4, 2.5, 5.2, and 8.7GHz). In this paper the full source catalogs from the 2.5, 5.2, and 8.7GHz observations are presented to complement Paper II (Huynh et al., 2005, Cat. J/AJ/130/1373) in this series, along with a detailed analysis of image quality and noise. We produce a consolidated catalog by matching sources across all four frequencies of our survey.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/288
- Title:
- Radio obs. of NGC 6251 jet
- Short Name:
- J/ApJ/833/288
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The structure of the NGC 6251 jet on the milliarcsecond scale is investigated using images taken with the European VLBI Network and the Very Long Baseline Array. We detect a structural transition of the jet from a parabolic to a conical shape at a distance of (1-2)x10^5^ times the Schwarzschild radius from the central engine, which is close to the sphere of gravitational influence of the supermassive black hole (SMBH). We also examine the jet pressure profiles with the synchrotron minimum energy assumption to discuss the physical origin of the structural transition. The NGC 6251 jet, together with the M87 jet, suggests a fundamental process of structural transition in the jets of active galactic nuclei (AGNs). Collimated AGN jets are characterized by their external galactic medium, showing that AGN jets interplay with the SMBH and its host galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/560/A23
- Title:
- Radio properties of faint BL Lacs
- Short Name:
- J/A+A/560/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The advent of Fermi is changing our understanding on the radio and gamma-ray emission in Active Galactic Nuclei. Contrary to pre-Fermi ideas, BL Lac objects are found to be the most abundant emitters in the gamma-ray band. However, since they are relatively weak radio sources, most of their parsec-scale structure and their multi-frequency properties are poorly understood and/or have not been investigated in a systematically fashion. Our main goal is to analyze the radio and gamma-ray emission properties of a sample of 42 BL Lacs selected, for the first time in the literature, with no constraint on their radio and gamma-ray flux densities/emission. Thanks to new Very Long Baseline Array observations at 8 and 15GHz for the whole sample, we present here fundamental parameters such as radio flux densities, spectral index information, and parsec-scale structure. Moreover, we search for gamma-ray counterparts using data reported in the Second Catalog of Fermi Gamma-ray sources. Parsec-scale radio emission is observed in the majority of the sources at both frequencies. Gamma-ray counterparts are found for 14/42 sources. The comparison between our results in radio and gamma-ray bands points out the presence of a large number of faint BL Lacs showing "non classical" properties such as low source compactness, core dominance, no gamma-ray emission and steep radio spectral indexes. A deeper multiwavelength analysis will be needed.
