V. Karamanavis

Radio jet emission from GeV-emitting narrow-line Seyfert 1 galaxies

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.

Multifrequency studies of the narrow-line Seyfert 1 galaxy SBS 0846+513

The narrow-line Seyfert 1 galaxy SBS0846+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 γ-ray flaring episodes from SBS0846+513 were observed in 2012 May and August, reaching a daily peak flux integrated above 100 MeV of (50±12)×10 8 ph cm 2 s 1 , and (73±14)×10 8 ph cm 2 s 1 on May 24 and August 7, respectively. Three outbursts were detected at 15 GHz

The F-GAMMA programme: multi-frequency study of active galactic nuclei in the Fermi era - Programme description and the first 2.5 years of monitoring

Context. 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 γ-ray blazars. We investigate its dependence on source class and examine whether the radio variability is related to the γ-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 228.39 GHz. 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 γ-ray fluxes. Results. 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 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 142.3 GHz correlate with 1 GeV fluxes at a significance level better than 3σ, implying that γ rays are produced very close to the mm-band emission region.

What powers the radio-loud narrow-line Seyfert 1 galaxy RX J2314.9+2243? - A view onto its central engine from radio to X-rays

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

PKS 1502+106: A high-redshift Fermi blazar at extreme angular resolution - Structural dynamics with VLBI imaging up to 86 GHz

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.

F-GAMMA: variability Doppler factors of blazars from multiwavelength monitoring

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

Zooming towards the Event Horizon - mm-VLBI today and tomorrow

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Inner jet kinematics and the viewing angle towards the γ-ray narrow-line Seyfert 1 galaxy 1H 0323+342

-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.

What can the 2008/10 broadband flare of PKS 1502+106 tell us? - Nuclear opacity, magnetic fields, and the location of γ rays

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.

An Exceptional Radio Flare in Markarian 421

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 (AGNs). 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 0323+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 six components with apparent speeds of ∼ 1 − 7 c , and one quasi-stationary feature. Combining the obtained apparent jet speed (β app ) and variability Doppler factor ( D var ) estimates together with other methods, we constrain the viewing angle θ towards 1H 0323+342 to θ ≤ 4 ° –13 ° . Using literature values of β app and D var , we also deduce a viewing angle of ≤8 ° –9 ° towards another radio- and γ-ray-loud NLS1, namely SBS 0846+513.