We studied the radio emission from four radio-loud and gamma-ray-loud narrow-line Seyfert 1 galaxies. The goal was to investigate whether a relativistic jet is operating at the source, and quantify its characteristics. We relied on the most systemati
c monitoring of such system in the cm and mm radio bands which is conducted with the Effelsberg 100 m and IRAM 30 m telescopes and covers the longest time-baselines and the most radio frequencies to date. We extract variability parameters and compute variability brightness temperatures and Doppler factors. The jet powers were computed from the light curves to estimate the energy output. The dynamics of radio spectral energy distributions were examined to understand the mechanism causing the variability. All the sources display intensive variability that occurs at a pace faster than what is commonly seen in blazars. The flaring events show intensive spectral evolution indicative of shock evolution. The brightness temperatures and Doppler factors are moderate, implying a mildly relativistic jet. The computed jet powers show very energetic flows. The radio polarisation in one case clearly implies a quiescent jet underlying the recursive flaring activity. Despite the generally lower flux densities, the sources appear to show all typical characteristics seen in blazars that are powered by relativistic jets.
Radio emission in blazars -- the aligned subset of Active Galactic Nuclei (AGN) -- is produced by synchrotron electrons moving relativistically in their jets magnetic field. Under the assumption of some degree of uniformity of the field, the emission
can be highly polarized -- linearly and circularly. In the radio regime, the observed variability is in most of the cases attributed to flaring events undergoing opacity evolution, i.e. transitions from optically thick to thin emission (or vice versa). These transistions have a specific signature in the polarization parameter space (angle and magnitude) which can be traced with high cadence polarization monitoring and provide us with a unique probe of the microphysics of the emitting region. Here we present the full Stokes analysis of radio emission from blazars observed in the framework of the F-GAMMA program and discuss the case study of PKS,1510$-$089 which has shown a prominent polarization event around MJD 55900.
The detection of gamma rays from a small number of Narrow Line Seyfert 1 galaxies by the LAT instrument onboard Fermi seriously challenged our understanding of AGN physics. Among the most important findings associated with their discovery has been th
e realisation that smaller-mass black holes seem to be hosted by these systems. Immediately after their discovery a radio multi- frequency monitoring campaign was initiated to understand their jet radio emission. Here the first results of the campaign are presented. The light curves and some first variability analyses are discussed, showing that the brightness temperatures and Doppler factors are moderate. The phenomenologies are typically blazar-like. The frequency domain on the other hand indicates intense spectral evolution and the variability patterns indicate mechanisms similar to those acting in the jets of BL Lacs and FSRQs. Finally, the linear polarisation also reveals the presence of a quiescent, optically thin jet in certain cases.
The F-GAMMA program is among the most comprehensive programs that aim at understanding the physics in active galactic nuclei through the multi-frequency monitoring of Fermi blazars. Here we discuss monthly sampled broad-band radio spectra (2.6 - 142
GHz). Two different studies are presented. (a) We discuss that the variability patterns traced can be classified into two classes: (1) to those showing intense spectral-evolution and (2) those showing a self-similar quasi-achromatic behaviour. We show that a simple two-component model can very well reproduce the observed phenomenologies. (b) We present the cm-to-mm behaviour of three gamma-ray bright Narrow Line Seyfert 1 galaxies over time spans varying between ~1.5 and 3 years and compare their variability characteristics with typical blazars.
The F-GAMMA program is a coordinated effort to investigate the physics of Active Galactic Nuclei (AGNs) via multi-frequency monitoring of Fermi blazars. In the current study we show and discuss the evolution of broad-band radio spectra, which are mea
sured at ten frequencies between 2.64 and 142 GHz using the Effelsberg 100-m and the IRAM 30-m telescopes. It is shown that any of the 78 sources studied can be classified in terms of their variability characteristics in merely 5 types of variability. It is argued that these can be attributed to only two classes of variability mechanisms. The first four types are dominated by spectral evolution and can be described by a simple two-component system composed of: (a) a steep quiescent spectral component from a large scale jet and (b) a time evolving flare component following the Shock-in-Jet evolutionary path. The fifth type is characterised by an achromatic change of the broad band spectrum, which could be attributed to a different mechanism, likely involving differential Doppler boosting caused by geometrical effects. Here we present the classification, the assumed physical scenario and the results of calculations that have been performed for the spectral evolution of flares.
Plancks all sky surveys at 30-857 GHz provide an unprecedented opportunity to follow the radio spectra of a large sample of extragalactic sources to frequencies 2-20 times higher than allowed by past, large area, ground-based surveys. We combine the
results of the Planck Early Release Compact Source Catalog (ERCSC) with quasi-simultaneous ground-based observations, as well as archival data, at frequencies below or overlapping Planck frequency bands, to validate the astrometry and photometry of the ERCSC radio sources and study the spectral features shown in this new frequency window opened by Planck. The ERCSC source positions and flux density scales are found to be consistent with the ground-based observations. We present and discuss the spectral energy distributions (SEDs) of a sample of extreme radio sources to illustrate the richness of the ERCSC for the study of extragalactic radio sources. Variability is found to play a role in the unusual spectral features of some of these sources.
Narrow-Line Seyfert 1 (NLS1) class of active galactic nuclei (AGNs) is generally radio-quiet, but a small percent of them are radio-loud. The recent discovery by Fermi/LAT of high-energy gamma-ray emission from 4 NLS1s proved the existence of relativ
istic jets in these systems. It is therefore important to study this new class of gamma-ray emitting AGNs. Here we report preliminary results about the observations of the July 2010 gamma-ray outburst of PMN J0948+0022, when the source flux exceeded for the first time 10^-6 ph cm^-2 s^-1 (E > 100 MeV).
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.
Within the context of investigating possible differences between the mechanisms at play in Radio Loud AGN and those in Radio Quiet ones, we study the spectral characteristics of a selected sample of Intermediate-Luminosity Broad-Line Radio Galaxies i
n X-rays, optical, IR and radio. Here, we present the radio spectra acquired with the 100-m radio telescope in Effelsberg between 2.6 and 32 GHz. These measurements reveal a large variety of spectral shapes urging for radio imaging that would disclose the source morphology. Such studies could potentially discriminate between different mechanisms.
