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Aims. The collimation of relativistic jets in galaxies is a poorly understood process. Detailed radio studies of the jet collimation region have been performed so far in few individual objects, providing important constraints for jet formation models. However, the extent of the collimation zone as well as the nature of the external medium possibly confining the jet are still debated. Methods. In this article we present a multi-frequency and multi-scale analysis of the radio galaxy NGC 315, including the use of mm-VLBI data up to 86 GHz, aimed at revealing the evolution of the jet collimation profile. We then consider results from the literature to compare the jet expansion profile in a sample of 27 low-redshift sources, mainly comprising radio galaxies and BL Lacs, classified based on the accretion properties as low-excitation (LEG) and high-excitation (HEG) galaxies. Results.The jet collimation in NGC 315 is completed on sub-parsec scales. A transition from a parabolic to conical jet shape is detected at $z_{t}=0.58\pm0.28$ parsecs or ${\sim}5\times 10^3$ Schwarzschild radii ($R_{S}$) from the central engine, a distance which is much smaller than the Bondi radius, $r_{B}{\sim}92$ $\rm pc$, estimated based on X-ray data. The jet in this and in few other LEGs in our sample may be initially confined by a thick disk extending out to ${\sim}10^3$-$10^4$ $R_{S}$. A comparison between the mass-scaled jet expansion profiles of all sources indicates that jets in HEGs are surrounded by thicker disk-launched sheaths and collimate on larger scales with respect to jets in LEGs. These results suggest that disk winds play an important role in the jet collimation mechanism, particularly in high-luminosity sources. The impact of winds for the origin of the FRI/FRII dichotomy in radio galaxies is also discussed., 14 pages plus appendix, 6 figures. Accepted for publication in A&A

In March 2018, Mukherjee (2018) reported the detection by VERITAS of very-high-energy emission (VHE; > 100 GeV) from 3C 264. This is the sixth, and second most distant, radio galaxy ever detected in the TeV regime. In this article we present a radio and X-ray analysis of the jet in 3C 264. We determine the main physical parameters of the parsec-scale flow and explore the implications of the inferred kinematic structure for radiative models of this gamma-ray emitting jet. The radio data set is comprised of VLBI observations at 15 GHz from the MOJAVE program, and cover a time period of ~2 years. Through a segmented wavelet decomposition method we estimate the apparent displacement of individual plasma features; we then perform a pixel-based analysis of the stacked image to determine the jet shape. The X-ray data set includes all available observations from the Chandra, XMM, and Swift satellites, and is used, together with archival data in the other bands, to build the SED. Proper motion is mostly detected along the edges of the flow, which appears strongly limb-brightened. The apparent speeds increase as a function of distance from the core up to a maximum of ~$11.5$ c. This constrains the jet viewing angle to assume relatively small values ($��\lesssim10^{\circ}$). In the acceleration region, extending up to a de-projected distance of ~$4.8\times10^4$ Schwarzschild radii (~$11$ pc), the jet is collimating ($r\propto z^{0.40\pm 0.04}$), as predicted for a magnetically-driven plasma flow. By assuming that the core region is indeed magnetically dominated ($U_B/U_e>1$), the SED and the jet power can be well reproduced in the framework of leptonic models, provided that the high-energy component is associated to a second emitting region. The possibility that this region is located at the end of the acceleration zone, either in the jet layer or in the spine, is explored in the modeling., 12 pages, 10 figures. Accepted for publication in Astronomy and Astrophysics

The advent of the Fermi-GST with its unprecedented capability to monitor the entire 4 pi sky within less than 2-3 hours, introduced new standard in time domain gamma-ray astronomy. To explore this new avenue of extragalactic physics the F-GAMMA programme undertook the task of conducting nearly monthly, broadband radio monitoring of selected blazars from January 2007 to January 2015. In this work we release all the light curves at 2.64, 4.85, 8.35, 10.45, 14.6, 23.05, 32, and 43 GHz and present first order derivative data products after all necessary post-measurement corrections and quality checks; that is flux density moments and spectral indices. The release includes 155 sources. The effective cadence after the quality flagging is around one radio SED every 1.3 months. The coherence of each radio SED is around 40 minutes. The released dataset includes more than $4\times10^4$ measurements. The median fractional error at the lowest frequencies (2.64-10.45 GHz) is below 2%. At the highest frequencies (14.6-43 GHz) with limiting factor of the atmospheric conditions, the errors range from 3% to 9%, respectively., Comment: Accepted for publication in Section: Catalogs and data of Astronomy & Astrophysics

Aims. We present a multifrequency, dense radio monitoring program of the blazar OJ 287 using the 100-m E elsberg radio telescope. The program aims to test different binary supermassive black hole (SMBH) scenarios and studying the physical conditions in the central region of this bright blazar. Here, we analyze the evolution in total flux density, linear and circular polarization as a means to study the OJ 287 jet structure and its magnetic field geometry. Methods.We used a recently developed, high-precision data analysis methodology to recover all four Stokes parameters.We measured the total flux density of OJ 287 at nine bands from 2.64 GHz to 43 GHz, the linear polarization parameters at four bands between 2.64 GHz and 10.45 GHz, and the circular polarization at two bands, 4.85 GHz and 8.35 GHz. The mean cadence of our measurements is ten days. Results. Between December 2015 and January 2017 (MJD 57370-57785), OJ 287 showed flaring activity and complex linear and circular polarization behavior. The radio electric vector position angle (EVPA) showed a large clockwise (CW) rotation by 340 with a mean rate of-1.04°/day. Based on concurrent very long baseline interferometric (VLBI) polarization data at 15 GHz and 43 GHz, the rotation seems to originate within the jet core at 43 GHz (projected angular size 0.15 mas or 0.67 pc at the redshift of the source). Moreover, optical polarization data show a similar monotonic CW rotation with a rate of about-1.1°/day which is superposed with shorter and faster rotations that exhibit rates of about 7.8°/day, mainly in the CW sense. Conclusions. The flux density and polarization variability of the single dish, VLBI and optical data is consistent with a polarized emission component propagating on a helical trajectory within a bent jet. We constrained the helix arc length to 0.26 pc and radius to 0.04 pc as well as the jet bending arc length projected on the plane of the sky to ≤1.9-7.6 pc. A similar bending has been observed also in high angular resolution VLBI images of the OJ 287 jet at its innermost regions. The helical trajectory covers only a part of the jet width, possibly its spine. In addition, our results indicate the presence of a stable polarized emission component. Its EVPA (-10°) is oriented perpendicular to the large scale jet, suggesting dominance of the poloidal magnetic field component. Finally, the EVPA rotation begins simultaneously with an optical flare and hence the two might be physically connected. That optical flare has been suggested to be linked to the interaction of a secondary SMBH with the inner accretion disk or originating in the jet of the primary.© 2018 ESO., This program is supported by Fermi Guest Investigator grants NNX08AW56G, NNX09AU10G, NNX12AO93G, and NNX15AU81G.

Recent population studies have shown that the variability Doppler factors can adequately describe blazars as a population. We use the flux density variations found within the extensive radio multi-wavelength datasets of the F-GAMMA program, a total of 10 frequencies from 2.64 up to 142.33 GHz, in order to estimate the variability Doppler factors for 58 $\gamma$-ray bright sources, for 20 of which no variability Doppler factor has been estimated before. We employ specifically designed algorithms in order to obtain a model for each flare at each frequency. We then identify each event and track its evolution through all the available frequencies for each source. This approach allows us to distinguish significant events producing flares from stochastic variability in blazar jets. It also allows us to effectively constrain the variability brightness temperature and hence the variability Doppler factor as well as provide error estimates. Our method can produce the most accurate (16\% error on average) estimates in the literature to date., Comment: 9 pages, 7 figures, accepted for publication in MNRAS

The Gamma-ray BL Lac object OJ 287 is known to exhibit inner-parsec "jet-wobbling", high degrees of variability at all wavelengths and quasi-stationary features including an apparent (~100 deg) position angle change in projection on the sky plane. Sub-50 micro-arcsecond resolution 86 GHz observations with the global mm-VLBI array (GMVA) supplement ongoing multi-frequency VLBI blazar monitoring at lower frequencies. Using these maps together with cm/mm total intensity and Gamma-ray observations from Fermi/LAT from 2008-2014, we aimed to determine the location of Gamma-ray emission and to explain the inner-mas structural changes. Observations with the GMVA offer approximately double the angular resolution compared with 43 GHz VLBA observations and allow us to observe above the synchrotron self-absorption peak frequency. The jet was spectrally decomposed at multiple locations along the jet. From this we derived estimates of the magnetic field. How the field decreases down the jet allowed an estimate of the distance to the jet apex and an estimate of the magnetic field strength at the jet apex and in the broad line region. Combined with accurate kinematics we attempt to locate the site of Gamma-ray activity, radio flares and spectral changes. Strong Gamma-ray flares appeared to originate from either the "core" region, a downstream stationary feature, or both, with Gamma-ray activity significantly correlated with radio flaring in the downstream quasi-stationary feature. Magnetic field estimates were determined at multiple locations along the jet, with the magnetic field found to be >1.6 G in the "core" and >0.4 G in the downstream quasi-stationary feature. We therefore found upper limits on the location of the "core" as >6.0 pc from the jet apex and determined an upper limit on the magnetic field near the jet base of the order of thousands of Gauss., 30 pages, 20 figures

Near-Eddington accretion rates onto low-mass black holes are thought to be a prime driver of the multi-wavelength properties of the narrow-line Seyfert 1 (NLS1) population of active galactic nuclei (AGN). Orientation effects have repeatedly been considered as another important factor involved, but detailed studies have been hampered by the lack of measured viewing angles towards this type of AGN. Here we present multi-epoch, 15 GHz VLBA images (MOJAVE program) of the radio-loud and Fermi/LAT-detected NLS1 galaxy 1H 323+342. These are combined with single-dish, multi-frequency radio monitoring of the source's variability, obtained with the Effelsberg 100-m and IRAM 30-m telescopes, in the course of the F-GAMMA program. The VLBA images reveal 6 components with apparent peeds of ~1 to ~7 c, and one quasi-stationary feature. Combining the obtained apparent jet speed ($\beta_{app}$) and variability Doppler factor ($D_{var}$) estimates together with other methods, we constrain the viewing angle towards 1H 0323+342 to $\theta \leq 4 - 13$ deg. Using literature values of $\beta_{app}$ and $D_{var}$, we also deduce a viewing angle of $\leq$ 8-9 deg towards another radio- and {\gamma}-ray-loud NLS1, namely SBS 0846+513., Comment: 16 pages, 3 figures, accepted for publication in Research in Astronomy and Astrophysics

To fully exploit the scientific potential of the Fermi mission, we initiated the F-GAMMA program. Between 2007 and 2015 it was the prime provider of complementary multi-frequency monitoring in the radio regime. 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. The F-GAMMA monitored monthly a sample of about 60 sources at up to twelve radio frequencies between 2.64 and 228.39 GHz. We perform a time series analysis on the first 2.5-year dataset 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 100-m and IRAM 30-m telescopes. All sources are variable across all frequency bands with amplitudes increasing with frequency up to rest frame frequencies of around 60 - 80 GHz as expected by shock-in-jet models. Compared to FSRQs, 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 as well as brightness temperatures and Doppler factors, than non-detected ones. Flux densities at 86.2 and 142.3 GHz correlate with 1 GeV fluxes at a significance level better than 3sigma, implying that gamma rays are produced very close to the mm-band emission region., Accepted for publication in section 4. Extragalactic astronomy of Astronomy and Astrophysics (18 pages, 9 figures)

Context. The origin of blazar variability, seen from radio up to gamma rays, is still a heavily debated matter and broadband flares offer a unique testbed towards a better understanding of these extreme objects. Such an energetic outburst was detected by Fermi/LAT in 2008 from the blazar PKS 1502+106. The outburst was observed from gamma rays down to radio frequencies. Aims. Through the delay between flare maxima at different radio frequencies, we study the frequency-dependent position of the unit-opacity surface and infer its absolute position with respect to the jet base. This nuclear opacity profile enables the magnetic field tomography of the jet. We also localize the gamma-ray emission region and explore the mechanism producing the flare. Methods. The radio flare of PKS 1502+106 is studied through single-dish flux density measurements at 12 frequencies in the range 2.64 to 226.5 GHz. To quantify it, we employ both a Gaussian process regression and a discrete cross-correlation function analysis. Results. We find that the light curve parameters (flare amplitude and cross-band delays) show a power-law dependence on frequency. Delays decrease with frequency, and the flare amplitudes increase up to about 43 GHz and then decay. This behavior is consistent with a shock propagating downstream the jet. The self-absorbed radio cores are located between about 10 and 4 pc from the jet base and their magnetic field strengths range between 14 and 176 mG, at the frequencies 2.64 to 86.24 GHz. Finally, the gamma-ray active region is located at (1.9 +/- 1.1) pc away from the jet base., 10 pages, 5 figures. Accepted for publication in A&A

Black holes, anywhere in the stellar-mass to supermassive range, are often associated with relativistic jets. Models suggest that jet production may be a universal process common in all black hole systems regardless of their mass. Although in many cases observations support such hypotheses for microquasars and Seyfert galaxies, little is known on whether boosted blazar jets also comply with such universal scaling laws. We use uniquely rich multiwavelength radio light curves from the F-GAMMA program and the most accurate Doppler factors available to date to probe blazar jets in their emission rest frame with unprecedented accuracy. We identify for the first time a strong correlation between the blazar intrinsic broad-band radio luminosity and black hole mass, which extends over $\sim$ 9 orders of magnitude down to microquasars scales. Our results reveal the presence of a universal scaling law that bridges the observing and emission rest frames in beamed sources and allows us to effectively constrain jet models. They consequently provide an independent method for estimating the Doppler factor, and for predicting expected radio luminosities of boosted jets operating in systems of intermediate or tens-of-solar mass black holes, immediately applicable to cases as those recently observed by LIGO., Comment: 13 pages, 4 figures, accepted for publication in APJ

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 systematic 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., Accepted for publication in 4 - Extragalactic astronomy of Astronomy and Astrophysics

In September 2012, the high-synchrotron-peaked (HSP) blazar Markarian 421 underwent a rapid wideband radio flare, reaching nearly twice the brightest level observed in the centimeter band in over three decades of monitoring. In response to this event we carried out a five epoch centimeter- to millimeter-band multifrequency Very Long Baseline Array (VLBA) campaign to investigate the aftermath of this emission event. Rapid radio variations are unprecedented in this object and are surprising in an HSP BL Lac object. In this flare, the 15 GHz flux density increased with an exponential doubling time of about 9 days, then faded to its prior level at a similar rate. This is comparable with the fastest large-amplitude centimeter-band radio variability observed in any blazar. Similar flux density increases were detected up to millimeter bands. This radio flare followed about two months after a similarly unprecedented GeV gamma-ray flare (reaching a daily E>100 MeV flux of (1.2 +/- 0.7)x10^(-6) ph cm^(-2) s^(-1)) reported by the Fermi Large Area Telescope (LAT) collaboration, with a simultaneous tentative TeV detection by ARGO-YBJ. A cross-correlation analysis of long-term 15 GHz and LAT gamma-ray light curves finds a statistically significant correlation with the radio lagging ~40 days behind, suggesting that the gamma-ray emission originates upstream of the radio emission. Preliminary results from our VLBA observations show brightening in the unresolved core region and no evidence for apparent superluminal motions or substantial flux variations downstream., 5 pages, 8 figures. Contributed talk at the meeting "The Innermost Regions of Relativistic Jets and Their Magnetic Fields", Granada, Spain. Updated to correct author list and references

The Fermi LAT detected an increase in γ-ray activity of the quasar 0836+710 (z=2.17) in Spring 2011 that culminated in a sharp γ-ray flare at the end of 2011 when the source reached a flux of 2.9×10−6 phot s−1cm−2 at 0.1-200 GeV. We monitor the quasar at optical wavelengths in photometric and polarimetric modes, at millimeter and centimeter wavelengths, and with the VLBA at 43 GHz. The optical brightness of the quasar increased by ~0.5 mag in R band and the degree of polarization oscillated between ~1% and ~6% during the highest γ-ray state, while the position angle of polarization rotated by ~300°. We have identified in the VLBA images a strong, highly polarized component that moves with an apparent speed of ~20 c. The component emerged from the core in the beginning of the γ-ray event and reached a flux maximum at the peak of the γ-ray outburst. We present the results of a correlative analysis of variations at different wavelengths along with the kinematic parameters of the parsec scale jet. We discuss the location of the high γ-ray emission in the relativistic jet, as well as the emission mechanisms responsible for γ-ray production.

The narrow-line Seyfert 1 galaxy SBS 0846+513 was first detected by the Large Area Telescope (LAT) on-board Fermi in 2011 June-July when it underwent a period of flaring activity. Since then, as Fermi continues to accumulate data on this source, its flux has been monitored on a daily basis. Two further gamma-ray flaring episodes from SBS 0846+513 were observed in 2012 May and August, reaching a daily peak flux integrated above 100 MeV of (50+/-12)x10^-8 ph/cm^2/s, and (73+/-14)x10^-8 ph/cm^2/s on May 24 and August 7, respectively. Three outbursts were detected at 15 GHz by the Owens Valley Radio Observatory 40-m telescope in 2012 May, 2012 October, and 2013 January, suggesting a complex connection with the gamma-ray activity. The most likely scenario suggests that the 2012 May gamma-ray flare may not be directly related to the radio activity observed over the same period, while the two gamma-ray flaring episodes may be related to the radio activity observed at 15 GHz in 2012 October and 2013 January. The gamma-ray flare in 2012 May triggered Swift observations that confirmed that SBS 0846+513 was also exhibiting high activity in the optical, UV and X-ray bands, thus providing a firm identification between the gamma-ray source and the lower-energy counterpart. We compared the spectral energy distribution (SED) of the flaring state in 2012 May with that of a quiescent state. The two SEDs, modelled as an external Compton component of seed photons from a dust torus, could be fitted by changing the electron distribution parameters as well as the magnetic field. No significant evidence of thermal emission from the accretion disc has been observed. Interestingly, in the 5 GHz radio luminosity vs. synchrotron peak frequency plot SBS 0846+513 seems to lie in the flat spectrum radio quasar part of the so-called `blazar sequence'., Comment: 11 pages, 9 figures, 4 tables. Accepted for publication in MNRAS

Context. Blazars are among the most energetic objects in the Universe. In 2008 August, Fermi/LAT detected the blazar PKS 1502+106 showing a rapid and strong gamma-ray outburst followed by high and variable flux over the next months. This activity at high energies triggered an intensive multi-wavelength campaign covering also the radio, optical, UV, and X-ray bands indicating that the flare was accompanied by a simultaneous outburst at optical/UV/X-rays and a delayed outburst at radio bands. Aims: In the current work we explore the phenomenology and physical conditions within the ultra-relativistic jet of the gamma-ray blazar PKS 1502+106. Additionally, we address the question of the spatial localization of the MeV/GeV-emitting region of the source. Methods: We utilize ultra-high angular resolution mm-VLBI observations at 43 and 86 GHz complemented by VLBI observations at 15 GHz. We also employ single-dish radio data from the F-GAMMA program at frequencies matching the VLBI monitoring. Results: PKS 1502+106 shows a compact core-jet morphology and fast superluminal motion with apparent speeds in the range 5--22 c. Estimation of Doppler factors along the jet yield values between ~7 up to ~50. This Doppler factor gradient implies an accelerating jet. The viewing angle towards the source differs between the inner and outer jet, with the former at ~3 degrees and the latter at ~1 degree, after the jet bends towards the observer beyond 1 mas. The de-projected opening angle of the ultra-fast, magnetically-dominated jet is found to be (3.8 +/- 0.5) degrees. A single jet component can be associated with the pronounced flare both at high-energies and in radio bands. Finally, the gamma-ray emission region is localized at less than 5.9 pc away from the jet base., Comment: 22 pages, 12 figures. Accepted for publication in A&A

Narrow-line Seyfert 1 (NLS1) galaxies are a sub-class of active galactic nuclei (AGN) with relatively low-mass black holes, accreting near the Eddington rate. A small fraction of them is radio-loud and harbors relativistic jets. As a class, these provide us with new insights into the cause(s) of radio-loudness, the blazar phenomenon at low black hole masses, and the operation of radio-mode feedback. The NLS1 galaxy RXJ2314.9+2243 is remarkable for its multi-wavelength properties. We present new radio observations taken at Effelsberg, and a summary of the recent results from our multi-wavelength study. RXJ2314.9+2243 is radio-loud, luminous in the infrared, has a flat X-ray spectrum and peculiar UV spectrum, and hosts an exceptionally broad and blueshifted [OIII]λ5007 emission line, indicating the presence of a strong outflow. RXJ2314.9+2243 likely represents an extreme case of AGN induced feedback in the local universe.

We present follow-up spectroscopy and photometry of 11 post common envelope binary (PCEB) candidates identified from multiple Sloan Digital Sky Survey (SDSS) spectroscopy in an earlier paper. Radial velocity measurements using the \Lines{Na}{I}{8183.27,8194.81} absorption doublet were performed for nine of these systems and provided measurements of six orbital periods in the range $\Porb= 2.7-17.4$ h. Three PCEB candidates did not show significant radial velocity variations in the follow-up data, and we discuss the implications for the use of SDSS spectroscopy alone to identify PCEBs. Differential photometry confirmed one of our spectroscopic orbital periods and provided one additional \Porb measurement. Binary parameters are estimated for the seven objects for which we have measured the orbital period and the radial velocity amplitude of the low-mass companion star, $K_\mathrm{sec}$. So far, we have published nine SDSS PCEBs orbital periods, all of them $\Porb1$ day, and that during the common envelope phase the orbital energy of the binary star is maybe less efficiently used to expell the envelope than frequently assumed., 13 pages, 8 figures, 5 tables Accepted in MNRAS

Aims. Radio-loud narrow-line type 1 galaxies provide us with a fresh look at the blazar phenomenon, the causes of radio loudness, and the physics of jet formation. We present a multi-wavelength study of the radio-loud narrow-line type 1 quasar RX J2314.9+2243, which exhibits some remarkable multi-wavelength properties. It is among the few radio-loud narrow-line type 1 galaxies, with a tentative γ-ray detection, is luminous in the infrared, and shows an exceptionally broad and blueshifted [OIII]λ5007 emission-line component. Methods. In order to understand the nature of this source, we have obtained optical, UV, X-ray, and radio observations of RX J2314.9+2243. Results. Its spectral energy distribution (SED) shows a broad hump extending between the IR and far-UV, a steep radio spectrum and flat X-ray spectrum. Its IR to far-UV SED is consistent with a scenario, in which synchrotron emission from a jet dominates the broadband emission, even though an absorption scenario cannot yet be fully excluded. The high blueshift of its very broad [OIII] component, 1260 km s −1 , is consistent with a face-on view, with the jet (and outflow) pointing towards us. RX J2314.9+2243 likely represents an

Narrow-line Seyfert 1 (NLS1) galaxies provide us with unique insights into the drivers of AGN activity under extreme conditions. Given their low black hole (BH) masses and near-Eddington accretion rates, they represent a class of galaxies with rapidly growing supermassive BHs in the local universe. Here, we present the results from our multi-frequency radio monitoring of a sample of {\gamma}-ray loud NLS1 galaxies ({\gamma}NLS1s), including systems discovered only recently, and featuring both the nearest and the most distant {\gamma}NLS1s known to date. We also present high-resolution radio imaging of 1H 0323+342, which is remarkable for its spiral or ring-like host. Finally, we present new radio data of the candidate {\gamma}-emitting NLS1 galaxy RX J2314.9+2243, characterized by a very steep radio spectrum, unlike other {\gamma}NLS1s., Comment: 4 pages, 1 figure. Accepted for publication in the Proceedings of the IAU Symposium No. 324: New Frontiers in Black Hole Astrophysics

Blazars are among the most variable objects in the universe. They feature energetic jets of plasma that launch from the cores of these active galactic nuclei (AGN), triggering activity from radio up to gamma-ray energies. Spatial localization of the region of their MeV/GeV emission is a key question in understanding the blazar phenomenon. The flat spectrum radio quasar (FSRQ) PKS 1502+106 has exhibited extreme and correlated, radio and high-energy activity that triggered intense monitoring by the Fermi-GST AGN Multi-frequency Monitoring Alliance (F-GAMMA) program and the Global Millimeter VLBI Array (GMVA) down to $\lambda$3 mm (or 86 GHz), enabling the sharpest view to date towards this extreme object. Here, we report on preliminary results of our study of the gamma-ray loud blazar PKS 1502+106, combining VLBI and single dish data. We deduce the critical aspect angle towards the source to be $\theta_{\rm c} = 2.6^{\circ}$, calculate the apparent and intrinsic opening angles and constrain the distance of the 86 GHz core from the base of the conical jet, directly from mm-VLBI but also through a single dish relative timing analysis. Finally, we conclude that gamma rays from PKS 1502+106 originate from a region between ~1-16 pc away from the base of the hypothesized conical jet, well beyond the bulk of broad-line region (BLR) material of the source., Comment: 4 pages, 1 figure, proceedings of the 12th European VLBI Network Symposium and Users Meeting - EVN 2014, 7-10 October 2014, Cagliari, Italy. Published online in PoS, PoS(EVN 2014)087

We present a pipeline that allows recovering reliable information for all four Stokes parameters with high accuracy. Its novelty relies on the treatment of the instrumental effects already prior to the computation of the Stokes parameters contrary to conventional methods, such as the M\"uller matrix one. The instrumental linear polarization is corrected across the whole telescope beam and significant Stokes $Q$ and $U$ can be recovered even when the recorded signals are severely corrupted. The accuracy we reach in terms of polarization degree is of the order of 0.1-0.2 %. The polarization angles are determined with an accuracy of almost 1$^{\circ}$. The presented methodology was applied to recover the linear and circular polarization of around 150 Active Galactic Nuclei. The sources were monitored from July 2010 to April 2016 with the Effelsberg 100-m telescope at 4.85 GHz and 8.35 GHz with a cadence of around 1.2 months. The polarized emission of the Moon was used to calibrate the polarization angle. Our analysis showed a small system-induced rotation of about 1$^{\circ}$ at both observing frequencies. Finally, we identify five sources with significant and stable linear polarization; three sources remain constantly linearly unpolarized over the period we examined; a total of 11 sources have stable circular polarization degree $m_\mathrm{c}$ and four of them with non-zero $m_\mathrm{c}$. We also identify eight sources that maintain a stable polarization angle over the examined period. All this is provided to the community for polarization observations reference. We finally show that our analysis method is conceptually different from the traditionally used ones and performs better than the M\"uller matrix method. Although it was developed for a system equipped with circularly polarized feeds it can easily be modified for systems with linearly polarized feeds as well., Comment: 19 pages, 17 figures, accepted for publication in Astronomy & Astrophysics on May 30, 2017

Radio emission in blazars -- the aligned subset of Active Galactic Nuclei (AGN) -- is produced by synchrotron electrons moving relativistically in their jet's 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., 4 pages, 1 figure, for the proceedings of the 11th Hellenic Astronomical Conference (Athens, Greece, September 8-12, 2013); 1 paragraph added in the last section; 1 reference added; minor changes in the text (mainly typos); minor changes in the text

Global VLBI imaging at millimeter and sub-millimeter wavelength overcomes the opacity barrier of synchrotron self-absorption in AGN and opens the direct view into sub-pc scale regions not accessible before. Since AGN variability is more pronounced at short millimeter wavelength, mm-VLBI can reveal structural changes in very early stages after outbursts. When combined with observations at longer wavelength, global 3mm and 1mm VLBI adds very detailed information. This helps to determine fundamental physical properties at the jet base, and in the vicinity of super-massive black holes at the center of AGN. Here we present new results from multi-frequency mm-VLBI imaging of OJ287 during a major outburst. We also report on a successful 1.3mm VLBI experiment with the APEX telescope in Chile. This observation sets a new record in angular resolution. It also opens the path towards future mm-VLBI with ALMA, which aims at the mapping of the black hole event horizon in nearby galaxies, and the study of the roots of jets in AGN., Comment: 6 pages, to appear in 11th European VLBI Network Symposium, ed. P. Charlot et al., Bordeaux (France), October 9-12, 2012