Results for "M. Kadler"

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Decomposing blazar spectra into lepto-hadronic emission componentsAug 16 2018Recently reported coincidences between high-energy neutrino events and major blazar outbursts reinforce the relevance of lepto-hadronic emission models for blazars. We study the influence of physical parameters on the neutrino output modeling blazar spectral ... More
Accessing the innermost regions of Active Galactic NucleiAug 21 2006Very-long-baseline interferometry can image the parsec-scale structure of radio jets, but the accretion disk close to the black hole remains invisible. One way to probe this accretion flow is provided by X-ray flux density monitoring and spectroscopy. ... More
Gamma-Ray Emission from the Broad-Line Radio Galaxy 3C111Aug 12 2008The broad-line radio galaxy 3C111 has been suggested as the counterpart of the gamma-ray source 3EGJ0416+3650. While 3C111 meets most of the criteria for a high-probability identification, like a bright flat-spectrum radio core and a blazar-like broadband ... More
Near infrared and gamma-ray monitoring of TANAMI gamma-ray bright sourcesJun 01 2013Spectral energy distribution and its variability are basic tools for understanding the physical processes operating in active galactic nuclei (AGN). In this paper we report the results of a one-year near infra red (NIR) and optical monitoring of a sample ... More
New Compton-thick AGN in the circumnuclear water maser hosts UGC3 789 and NGC 6264Sep 25 2013Large column densities, derived from X-ray studies, are typically measured towards AGN hosting water masers, especially when the H2O emission is associated with the nuclear accretion disk. In addition, possible correlations between the intrinsic X-ray ... More
TANAMI - Multiwavelength and Multimessenger Observations of Active GalaxiesJun 12 2015Jul 08 2015Extragalactic jets launched from the immediate vicinity of supermassive black holes in radio-loud active galactic nuclei (AGN) are key objects in modern astronomy and astroparticle physics. AGN jets carry a fraction of the total gravitational energy released ... More
X-ray emission from the blazar AO 0235+16: the XMM-Newton and Chandra point of viewMar 14 2006Mar 15 2006In this paper we analyse five observations of the BL Lac object AO 0235+16 performed with the Chandra and XMM-Newton satellites during the years 2000-2005. In the February 2002 observation the source is found in a bright state and presents a steep X-ray ... More
Multifrequency variability of the blazar AO 0235+164. The WEBT campaign in 2004-2005 and long-term SED analysisAug 29 2006A huge multiwavelength campaign targeting the blazar AO 0235+164 was organized by the Whole Earth Blazar Telescope (WEBT) in 2003-2005 to study the variability properties of the source. Monitoring observations were carried out at cm and mm wavelengths, ... More
The WEBT campaign to observe AO 0235+16 in the 2003-2004 observing seasonMar 15 2005A multiwavelength campaign on the BL Lac object AO 0235+16 has been organized by the WEBT collaboration during the observing seasons 2003-2004 and 2004-2005. Here we report on the results of the first season, which saw the participation of 24 optical ... More
Radio spectra of intermediate-luminosity broad-line radio galaxiesJul 25 2008Within 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 in ... More
Asymmetric jet production in the Active Galactic Nucleus of NGC1052Jan 09 2019Context: Few Active Galactic Nuclei (AGN) reveal a double sided jet system. However, these are crucial to understand basic physical properties of extragalactic jets. Aims: We address the questions whether jets in AGN are symmetric in nature, how well ... More
Southern-Hemisphere AGN Monitoring on (Sub-)Parsec Scales: The TANAMI ProgramMay 07 2012The Very Long Baseline Interferometry (VLBI) monitoring program TANAMI provides bi-monthly, dualfrequency (8GHz and 22GHz) observations of extragalactic jets with milliarcsecond resolution south of -30 deg declination using the Australian Long Baseline ... More
Consequences of a possible jet-star interaction in the inner central parsec of Centaurus AFeb 10 2015Apr 24 2015The jet-counterjet system of the closest radio-loud active galaxy Centaurus A (Cen A) can be studied with Very Long Baseline Interferometry (VLBI) on unprecedented small linear scales of ~0.018pc. These high-resolution observations provide essential information ... More
High-resolution studies of the twin jet in NGC 1052Dec 01 2008The radio loud galaxy NGC 1052 is being studied in an intensive multi-band campaign including X-ray brigthness monitoring and spectroscopic observations, single-dish radio brightness monitoring at centimetre wavelengths, and a high-frequency very-long-baseline ... More
Hydrodynamics of a perturbation in the jet of 3C111Sep 03 2008Sep 09 2008We present results on the modelling of the ejection of a superluminal component in the jet of 3C111. We propose that the component is generated by an injection of dense material followed by a decrease in the injection rate of bulk particles in the jet. ... More
X-ray vs. water maser emission in AGNDec 14 2009Correlations between X-ray and water maser emission in AGN have been recently reported. However, the lack of systematic studies affects the confidence level of these results. In the following, we introduce a project aimed at studying all the water maser ... More
The Twin--Jet System in NGC 1052: VLBI-Scrutiny of the Obscuring TorusJul 14 2004NGC 1052 offers the possibility to study the obscuring torus around a supermassive black hole, predicted by the standard model of active galactic nuclei, over a wide range of wavelengths from the radio to the X-ray regime. We present a detailed VLBI study ... More
The gamma-ray properties of radio-selected extragalactic jetsJun 13 2010Most extragalactic jets in radio-loud Active Galactic Nuclei are bright and variable gamma-ray sources, which are continuously monitored with Fermi/LAT. We present the gamma-ray properties of the MOJAVE and TANAMI AGN samples of radio-loud AGN. Both programs ... More
On the nature of an ejection event in the jet of 3C111Aug 25 2008We present a possible scenario for the ejection of a superluminal component in the jet of the Broad Line Radio Galaxy 3C111 in early 1996. VLBI observations at 15 GHz discovered the presence of two jet features on scales smaller than one parsec. The first ... More
A Quasi-Periodic Modulation of the Radio Light Curve of the Blazar PKS B0048-097May 23 2006Jun 27 2006In this letter we present the results of a wavelet analysis of the radio light curve of the BL Lac Object PKS B0048-097 from the University of Michigan Radio Astronomy Observatory monitoring program at 8GHz during twenty-five years, from 1979 to 2004. ... More
Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. II. Additional SourcesMay 06 2002We report further results from our imaging survey at 15GHz (lambda=2 cm) with the Very Long Baseline Array. This paper presents single epoch images for 39 sources, bringing the total number of objects in the sample to 171. Our sample is representative ... More
X-Raying the MOJAVE Sample of Compact Extragalactic Radio JetsApr 11 2007The MOJAVE sample is the first large radio-selected, VLBI-monitored AGN sample for which complete X-ray spectral information is being gathered. We report on the status of Swift survey observations which complement the available archival X-ray data at ... More
Multi-frequency & Multi-epoch VLBI study of Cygnus ASep 15 2003We present the first multi-frequency phase-referenced observations of Cygnus A done with the VLBA at 15 and 22 GHz. We find a pronounced two-sided jet structure, with a steep spectrum along the jet and a highly inverted spectrum towards the counter-jet. ... More
Spectral Properties of the Core and the VLBI-Jets of Cygnus ASep 14 2004We present a detailed VLBI study of the spectral properties of the inner core region of the radio galaxy Cygnus A at 5 GHz, 15 GHz, 22 GHz, 43 GHz and 86 GHz. Our observations include an epoch using phase-referencing at 15 GHz and 22 GHz and the first ... More
Combined VLBI- and X-ray Observations of Active Galactic NucleiSep 13 2004Compact radio cores in radio-loud active galactic nuclei (AGNs) are classical targets of Very-Long-Baseline interferometric (VLBI) research. Until today little has been known about their X-ray properties in comparison to radio-quiet AGNs. Here, we present ... More
Jet emission in NGC1052 at radio, optical, and X-ray frequenciesMar 08 2004We present a combined radio, optical, and X-ray study of the nearby LINER galaxy NGC 1052. Data from a short (2.3 ksec) {\it CHANDRA} observation of NGC 1052 reveal the presence of various jet-related X-ray emitting regions, a bright compact core and ... More
Radio-optical scrutiny of the central engine in compact AGNNov 16 2004Nov 29 2004We combine Very-Long-Baseline Interferometry (VLBI) data for $\sim100$ active galactic nuclei (AGN) available from the Very Large Baseline Array (VLBA) 2 cm imaging survey and optical spectroscopy to investigate the relationships in the emission-line ... More
Constraining the magnetic field in the parsec-scale jets of the brightest Fermi blazars with multifrequency VLBI observationsJan 15 2010Jan 18 2010The spatially resolved broad-band spectroscopy with Very Long Baseline Interferometry (VLBI) is one of the few methods that can probe the physical conditions inside blazar jets. We report on measurements of the magnetic field strength in parsec-scale ... More
A Multiband Approach to AGN: Radioscopy & Radio AstronomyNov 18 2004Only in the radio-loud population of active galactic nuclei (AGN) does the production, collimation, and acceleration of powerful relativistic jets take place. We introduce here a concept of combined VLBI- and X-ray spectroscopic observations of sources ... More
The spectral energy distribution of gamma-faint compact radio sourcesJan 10 2010MOJAVE is a VLBI program which monitors a statistically complete, radio-selected sample of 135 relativistically beamed, flat-spectrum active galactic nuclei for over more than a decade. In order to understand the high-energy behavior of this radio complete ... More
NGC1052 - A study of the pc-scale twin jetApr 03 2002We present results of a VLBA multi-frequency study of the pc-scale twin jet in NGC1052. We observed this object at epoch 1998.99 with the VLBA at 5, 8.4, 22 and 43 GHz both in total and linearly polarized intensity. The spectral analysis confirms the ... More
Probes of Jet-Disk-Coupling in AGN from Combined VLBI and X-Ray ObservationsJul 09 2004The formation of powerful extragalactic jets is not well understood at present as well as the associated key question:``What makes an AGN radio loud?''. Here we discuss how the combination of VLBI and X-ray spectroscopic observations allows the inter-relation ... More
Radio and Gamma-ray Properties of Extragalactic Jets from the TANAMI SampleJan 19 2016Using high-resolution radio imaging with VLBI techniques, the TANAMI program has been observing the parsec-scale radio jets of southern (declination south of -30{\deg}) gamma-ray bright AGN simultaneously with Fermi/LAT monitoring of their gamma-ray emission. ... More
Kinematics of AGN and Quasar JetsMar 09 2008The major multi-epoch VLBA programs are described and discussed in terms of relativistic beaming models. Broadly speaking the observed kinematics are consistent with models having a parent population which is only mildly relativistic but with Lorentz ... More
Sub-parsec scale imaging of Centaurus AJun 08 2010Jul 08 2010At a distance of about 3.8 Mpc, the radio galaxy Centaurus A is the closest active galaxy. Therefore it is a key target for studying the innermost regions of active galactic nuclei (AGN). VLBI observations conducted within the framework of the TANAMI ... More
Detecting Radio Frequency Interference in radio-antenna arrays with the Recurrent Neural Network algorithmAug 29 2018Signal artefacts due to Radio Frequency Interference (RFI) are a common nuisance in radio astronomy. Conventionally, the RFI-affected data are tagged by an expert data analyst in order to warrant data quality. In view of the increasing data rates obtained ... More
Fermi-LAT counterparts of IceCube neutrinos above 100 TeVOct 19 2018The IceCube Collaboration has published four years of data and the observed neutrino flux is significantly in excess of the expected atmospheric background. Due to the steeply falling atmospheric background spectrum, events at the highest energies are ... More
Catching the Radio Flare in CTA 102 III. Core-Shift and Spectral AnalysisJun 26 2013The temporal and spatial spectral evolution of the jets of AGN can be studied with multi-frequency, multi-epoch VLBI observations. The combination of both, morphological and spectral parameters can be used to derive source intrinsic physical properties ... More
Relativistic Beaming and the Intrinsic Properties of Extragalactic Radio JetsNov 20 2006Relations between the observed quantities for a beamed radio jet, apparent transverse speed and apparent luminosity (beta_app,L), and the intrinsic quantities, Lorentz factor and intrinsic luminosity (gamma,L_o), are investigated. The inversion from measured ... More
Relativistic beaming and gamma-ray brightness of blazarsNov 25 2009Jan 19 2010We investigate the dependence of gamma-ray brightness of blazars on intrinsic properties of their parsec-scale radio jets and the implication for relativistic beaming. By combining apparent jet speeds derived from high-resolution VLBA images from the ... More
Multiwavelength campaign of the gamma-ray flaring source PKS 2052-47Jan 10 2010The flat-spectrum radio quasar PKS 2052-47 experienced an optical flare in July-August, 2009. On August 9, the LAT detector onboard Fermi observed a flare from the source, which reached its active phase in the following two months. To further investigate ... More
High Resolution Rapid Response observations of compact radio sources with the Ceduna Hobart Interferometer (CHI)Jan 25 2012Context. Frequent, simultaneous observations across the electromagnetic spectrum are essential to the study of a range of astrophysical phenomena including Active Galactic Nuclei. A key tool of such studies is the ability to observe an object when it ... More
Powering the Jets in NGC1052Oct 26 2008We have studied the inner regions of the LINER galaxy NGC1052 since the mid 1990s at high resolution with 15 GHz very-long-baseline interferometry observations. A compact, two-sided jet structure is revealed, with multiple sub-parsec scale features moving ... More
The MHz-peaked radio spectrum of the unusual gamma-ray source PMN J1603-4904Sep 07 2016Context. The majority of bright extragalactic gamma-ray sources are blazars. Only a few radio galaxies have been detected by Fermi/LAT. Recently, the GHz-peaked spectrum source PKS 1718-649 was confirmed to be gamma-ray bright, providing further evidence ... More
The Twin-Jet of NGC1052 at Radio, Optical, and X-ray FrequenciesMar 14 2003We present results from a combined radio, optical, and X-ray study of the jet-associated emission features in NGC1052. We analyse the radio-optical morphology and find a good positional correlation between the radio jet and the optical emission cone. ... More
Extragalactic H_2O masers and X-ray absorbing column densitiesDec 17 2005Having conducted a search for the 22 GHz water vapor line towards galaxies with nuclear activity, large nuclear column densities or high infrared luminosities, we present H_2O spectra for NGC2273, UGC5101 and NGC3393 with isotropic luminosities of 7, ... More
Catching the radio flare in CTA 102: II. VLBI kinematic analysisNov 15 2012We performed multifrequency multiepoch Very Long Baseline Array (VLBA) observations of the blazar CTA 102 during its 2006 radio flare, the strongest ever reported for this source. These observations provide an excellent opportunity to investigate the ... More
The Gamma-Ray Blazar PKS 0208-512, a Multi-Wavelength InvestigationFeb 21 2012Jun 27 2012The gamma-ray blazar PKS 0208-512 has shown strong periods of flaring, at all frequencies from radio to gamma-ray. This has led to its inclusion in the TANAMI project, which tracks the jets of southern AGN using VLBI as well as supporting flux density ... More
The TANAMI Program: Southern-Hemisphere AGN on (Sub-)parsec ScalesJan 18 2013The Southern Hemisphere VLBI monitoring program TANAMI provides dual-frequency (8 GHz and 22 GHz), milliarcsecond monitoring of extragalactic jets south of -30 degrees declination. The TANAMI sample consists of a combined radio and gamma-ray selected ... More
Intrinsic Brightness Temperatures of AGN JetsMar 30 2006We present a new method for studying the intrinsic brightness temperatures of the parsec-scale jet cores of Active Galactic Nuclei (AGN). Our method uses observed superluminal motions and observed brightness temperatures for a large sample of AGN to constrain ... More
MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. VI. Kinematics Analysis of a Complete Sample of Blazar JetsSep 28 2009We discuss the jet kinematics of a complete flux-density-limited sample of 135 radio-loud active galactic nuclei (AGN) resulting from a 13 year program to investigate the structure and evolution of parsec-scale jet phenomena. Our analysis is based on ... More
MOJAVE: Monitoring of Jets in AGN with VLBA Experiments. VII. Blazar Jet AccelerationSep 28 2009We discuss acceleration measurements for a large sample of extragalactic radio jets from the MOJAVE program which studies the parsec-scale jet structure and kinematics of a complete, flux-density-limited sample of Active Galactic Nuclei (AGN). Accelerations ... More
Kinematics of parsec-scale structures in AGN: the 2cm VLBA SurveyJul 01 2002We are investigating the kinematics of jets in active galactic nuclei on parsec scales by studying a representative population of sources. This study is being carried out using the Very Long Baseline Array at 15 GHz, with more than 800 images taken since ... More
Investigating source confusion in PMN J1603$-$4904Jan 05 2018PMN J1603$-$4904 is a likely member of the rare class of $\gamma$-ray emitting young radio galaxies. Only one other source, PKS 1718$-$649, has been confirmed so far. These objects, which may transition into larger radio galaxies, are a stepping stone ... More
Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei III. Kinematics of Parsec-Scale Radio JetsMar 13 2004We report the results of a 15 GHz (2 cm) multi-epoch VLBA program, begun in 1994 to study the outflow in radio jets ejected from quasars and active galaxies. The observed flow of 208 distinct features measured in 110 quasars, active galaxies, and BL Lac ... More
Jet Collimation in Action: Re-alignment on Kiloparsec Scales in 3C279Apr 08 2003Apr 30 2003We report a change in the trajectory of a well studied jet component of the quasar 3C279. The component changes in apparent projected speed and direction, and we find it to be moving with a Lorentz factor gamma >~ 15 at an initial angle of <~ 1 degree ... More
The broadband emission properties of AGN jetsJan 17 2011The origin of the high-energy emission of blazars is still a matter of debate. To investigate the emission mechanism of extragalactic outflows and to pin down the location of the emission, we have constructed a broadband spectral energy distribution (SED) ... More
A Suzaku, NuSTAR, and XMM-Newton view on variable absorption and relativistic reflection in NGC 4151Mar 31 2017We disentangle X-ray disk reflection from complex line-of-sight absorption in the nearby Seyfert NGC 4151, using a suite of Suzaku, NuSTAR, and XMM-Newton observations. Extending upon earlier published work, we pursue a physically motivated model using ... More
The Broadband Spectral Energy Distribution of the MOJAVE SampleJun 24 2010We are constructing the broadband SED catalog of the MOJAVE sample from the radio to the gamma-ray band using MOJAVE, Swift UVOT/XRT/BAT, and Fermi/LAT data, in order to understand the emission mechanism of extragalactic outflows and to investigate the ... More
ATCA monitoring of gamma-ray loud AGNMay 10 2012As a critical part of the Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry (TANAMI) program, in November 2007 the Australia Telescope Compact Array (ATCA) started monitoring the radio spectra of a sample of southern hemisphere ... More
Exploring the bulk of the BL Lac object population:1. parsec-scale radio structuresSep 11 2013Context. 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 ... More
Insights into the particle acceleration of a peculiar gamma -ray radio galaxy IC 310Feb 04 2015IC 310 has recently been identified as a gamma-ray emitter based on observations at GeV energies with Fermi-LAT and at very high energies (VHE, E > 100 GeV) with the MAGIC telescopes. Despite IC 310 having been classified as a radio galaxy with the jet ... More
A Connection Between Apparent VLBA Jet Speeds and Initial Active Galactic Nucleus Detections Made by the Fermi Gamma-ray ObservatoryFeb 12 2009Mar 31 2009In its first three months of operations, the Fermi Gamma-Ray Observatory has detected approximately one quarter of the radio-flux-limited MOJAVE sample of bright flat-spectrum active galactic nuclei (AGNs) at energies above 100 MeV. We have investigated ... More
The Parsec-scale Structure, Kinematics, and Polarization of Radio-Loud Narrow-Line Seyfert 1 GalaxiesNov 04 2014Nov 10 2014Several narrow-line Seyfert 1 galaxies (NLS1s) have now been detected in gamma rays, providing firm evidence that at least some of this class of active galactic nuclei (AGN) produce relativistic jets. The presence of jets in NLS1s is surprising, as these ... More
The EVN view of the highly variable TeV active galaxy IC 310Feb 12 2015Very-high-energy $\gamma$-ray observations of the active galaxy IC 310 with the MAGIC telescopes have revealed fast variability with doubling time scales of less than 4.8min. This implies that the emission region in IC 310 is smaller than 20% of the gravitational ... More
Inner jet kinematics and the viewing angle towards the γ-ray narrow-line Seyfert 1 galaxy 1H 0323+342Aug 10 2016Near-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 ... More
GRIPS - Gamma-Ray Imaging, Polarimetry and SpectroscopyMay 06 2011We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range. The Gamma-Ray Imaging, Polarimetry and Spectroscopy ... More
A Highly Magnetized Twin-Jet Base Pinpoints a Supermassive Black HoleMay 23 2016May 24 2016Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical models based on Blandford & Znajek extract the rotational energy from a Kerr black hole, which could be the case for NGC1052, ... More
Doppler Boosting, Superluminal Motion, and the Kinematics of AGN JetsAug 23 2007We discuss results from a decade long program to study the fine-scale structure and the kinematics of relativistic AGN jets with the aim of better understanding the acceleration and collimation of the relativistic plasma forming AGN jets. From the observed ... More
Radio continuum of galaxies with H$_{2}$O megamaser disks: 33 GHz VLA dataJun 08 2017We investigate the nuclear environment of galaxies with observed 22 GHz water megamaser in their subparsec edge-on accretion disks, using 33 GHz (9mm) radio continuum data from VLA, with a resolution of ~ 0.2-0.5 arcsecs, and relate the maser and host ... More
Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine Scale StructureMay 26 2005Jul 08 2005We have used VLBA fringe visibility data obtained at 15 GHz to examine the compact structure in 250 extragalactic radio sources. For 171 sources in our sample, more than half of the total flux density seen by the VLBA remains unresolved on the longest ... More
On the relation between AGN gamma-ray emission and parsec-scale radio jetsFeb 12 2009Mar 27 2009We 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 ... More
Accretion disk versus jet orientation in H$_{2}$O megamaser galaxiesFeb 14 2019An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc sized accretion disks. Because of the small linear and angular scales involved, this alignment has ... More
MOJAVE: Monitoring of Jets in AGN with VLBA Experiments. V. Multi-epoch VLBA ImagesDec 20 2008We present images from a long term program (MOJAVE: Monitoring of Jets in AGN with VLBA Experiments) to survey the structure and evolution of parsec-scale jet phenomena associated with bright radio-loud active galaxies in the northern sky. The observations ... More
The Trails of Superluminal Jet Components in 3C111Jan 04 2008Jan 07 2008In 1996, a major radio flux-density outburst occured in the broad-line radio galaxy 3C111. It was followed by a particularly bright plasma ejection associated with a superluminal jet component, which has shaped the parsec-scale structure of 3C111 for ... More
Spectral Analysis of the Accretion Flow in NGC 1052 with SuzakuMar 20 2009We present an analysis of the 101 ks, 2007 Suzaku spectrum of the LINER galaxy NGC 1052. The 0.5-10 keV continuum is well-modeled by a power-law modified by Galactic and intrinsic absorption, and it exhibits a soft, thermal emission component below 1 ... More
The first scientific experiment using Global e-VLBI observations: a multiwavelength campaign on the gamma-ray Narrow-Line Seyfert 1 PMN J0948+0022Dec 13 2010The detection of gamma-ray emission by Fermi-LAT from the radio loud Narrow Line Seyfert 1 PMN J0948+0022 (Abdo et al. 2009, ApJ 699, 976) triggered a multi-wavelength campaign between March and July 2009. Given its high compactness (Doi et al. 2006, ... More
PKS 2123-463: a confirmed gamma-ray blazar at high redshiftSep 03 2012The flat spectrum radio quasar (FSRQ) PKS 2123-463 was associated in the First Fermi-LAT source catalog with the gamma-ray source 1FGL J2126.1-4603, but when considering the full first two years of Fermi observations, no gamma-ray source at a position ... More
From Radio to TeV: The surprising Spectral Energy Distribution of AP LibraeJun 02 2015Sep 21 2015Following the discovery of high-energy (HE; $E>10\,{\rm MeV}$) and very-high-energy (VHE; $E>100\,{\rm GeV}$) $\gamma$-ray emission from the low-frequency-peaked BL~Lac (LBL) object AP Librae, its electromagnetic spectrum is studied over 60 octaves in ... More
A redshifted Fe K$α$ line from the unusual gamma-ray source PMN J1603-4904Jan 05 2015Multiwavelength observations have revealed the highly unusual properties of the gamma-ray source PMN J1603-4904, which are difficult to reconcile with any other well established gamma-ray source class. The object is either a very atypical blazar or compact ... More
Millimetre-VLBI Monitoring of AGN with Sub-milliarcsecond ResolutionSep 14 2004Global millimetre VLBI allows detailed studies of the most central jet regions of AGN with unprecedent spatial resolution of a few 100-1000 Schwartzschild radii to be made. Study of these regions will help to answer the question how the highly relativistic ... More
Structural variability of 3C 111 on parsec scalesOct 06 2011Jan 16 2012We discuss the parsec-scale structural variability of the extragalactic jet 3C 111 related to a major radio flux density outburst in 2007. The data analyzed were taken within the scope of the MOJAVE, UMRAO, and F-GAMMA programs, which monitor a large ... More
Constraints on the gamma-ray emitting region in blazars from multi-frequency VLBI measurementsJun 15 2010Single-zone synchrotron self-Compton and external Compton models are widely used to explain broad-band Spectral Energy Distributions (SEDs) of blazars from infrared to gamma-rays. These models bear obvious similarities to the homogeneous synchrotron cloud ... More
A Search for Cosmic Neutrino and Gamma-Ray Emitting Transients in 7.3 Years of ANTARES and Fermi LAT DataApr 12 2019We analyze 7.3 years of ANTARES high-energy neutrino and Fermi LAT {\gamma}-ray data in search of cosmic neutrino + {\gamma}-ray ({\nu}+{\gamma}) transient sources or source populations. Our analysis has the potential to detect either individual {\nu}+{\gamma} ... More
A Variable-Density Absorption Event in NGC 3227 mapped with Suzaku and SwiftAug 19 2015The morphology of the circumnuclear gas accreting onto supermassive black holes in Seyfert galaxies remains a topic of much debate. As the innermost regions of Active Galactic Nuclei (AGN) are spatially unresolved, X-ray spectroscopy, and in particular ... More
Unusual Flaring Activity in the Blazar PKS 1424-418 during 2008-2011Jul 01 2014Aug 07 2014Context. Blazars are a subset of active galactic nuclei (AGN) with jets that are oriented along our line of sight. Variability and spectral energy distribution (SED) studies are crucial tools for understanding the physical processes responsible for observed ... More
Global e-VLBI observations of the gamma-ray narrow line Seyfert 1 PMN J0948+0022Feb 16 2011There is growing evidence of relativistic jets in radio-loud narrow-line Seyfert 1 (RL-NLS1) galaxies. We constrain the observational properties of the radio emission in the first RL-NLS1 galaxy ever detected in gamma-rays, PMN J0948+0022, i.e., its flux ... More
VLBA polarimetric monitoring of 3C 111Nov 05 2017We aim to better understand the dynamics within relativistic magneto-hydrodynamical flows in the extreme environment and close vicinity of supermassive black holes. To do so, we analyze the peculiar radio galaxy 3C 111, for which long-term polarimetric ... More
TANAMI monitoring of Centaurus A: The complex dynamics in the inner parsec of an extragalactic jetJul 01 2014Oct 01 2014Centaurus A is the closest radio-loud active galaxy. Very Long Baseline Interferometry (VLBI) enables us to study the jet-counterjet system on milliarcsecond (mas) scales, providing essential information for jet emission and propagation models. We study ... More
Neutrinos, Cosmic Rays and the MeV BandMar 13 2019The possible association of the blazar TXS 0506+056 with a high-energy neutrino detected by IceCube holds the tantalizing potential to answer three astrophysical questions: 1. Where do high-energy neutrinos originate? 2. Where are cosmic rays produced ... More
Extended X-ray emission in PKS 1718$-$649Apr 11 2018PKS 1718$-$649 is one of the closest and most comprehensively studied candidates of a young active galactic nucleus (AGN) that is still embedded in its optical host galaxy. The compact radio structure, with a maximal extent of a few parsecs, makes it ... More
PKS 1954-388: RadioAstron Detection on 80,000 km Baselines and Multiwavelength ObservationsMay 05 2017We present results from a multiwavelength study of the blazar PKS 1954-388 at radio, UV, X-ray, and gamma-ray energies. A RadioAstron observation at 1.66 GHz in June 2012 resulted in the detection of interferometric fringes on baselines of 6.2 Earth-diameters. ... More
Dual-frequency VLBI study of Centaurus A on sub-parsec scalesApr 05 2011Centaurus A is the closest active galactic nucleus. High resolution imaging using Very Long Baseline Interferometry (VLBI) enables us to study the spectral and kinematic behavior of the radio jet-counterjet system on sub-parsec scales, providing essential ... More
The Gamma-Ray Emitting Radio-Loud Narrow-Line Seyfert 1 Galaxy PKS 2004-447 II. The Radio ViewNov 09 2015Gamma-ray detected radio-loud narrow-line Seyfert 1 (g-NLS1) galaxies constitute a small but interesting sample of the gamma-ray loud AGN. The radio-loudest g-NLS1 known, PKS 2004-447, is located in the southern hemisphere and is monitored in the radio ... More
TANAMI: Milliarcsecond Resolution Observations of Extragalactic Gamma-ray SourcesDec 31 2009The TANAMI (Tracking AGN with Austral Milliarcsecond Interferometry) and associated programs provide comprehensive radio monitoring of extragalactic gamma-ray sources south of declination -30 degrees. Joint quasi-simultaneous observations between the ... More
TANAMI: Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry - II. Additional SourcesSep 10 2017Sep 25 2017TANAMI is a multiwavelength program monitoring active galactic nuclei (AGN) south of -30deg declination including high-resolution Very Long Baseline Interferometry (VLBI) imaging, radio, optical/UV, X-ray and gamma-ray studies. We have previously published ... More
The unusual multiwavelength properties of the gamma-ray source PMNJ1603-4904Dec 16 2013We investigate the nature and classification of PMNJ1603-4904, a bright radio source close to the Galactic plane, which is associated with one of the brightest hard-spectrum gamma-ray sources detected by Fermi/LAT. It has previously been classified as ... More
TANAMI - Tracking Active Galactic Nuclei with Austral Milliarcsecond InterferometryDec 19 2009Jan 18 2010We present a summary of the observation strategy of TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry), a monitoring program to study the parsec-scale structure and dynamics of relativistic jets in active galactic nuclei ... More
The TANAMI ProgramDec 03 2009TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) is a monitoring program to study the parsec-scale structures and dynamics of relativistic jets in active galactic nuclei (AGN) of the Southern Hemisphere with the Long ... More
NuSTAR and XMM-Newton Observations of the Hard X-Ray Spectrum of Centaurus ANov 05 2015Jan 25 2016We present simultaneous XMM-Newton and NuSTAR observations spanning 3-78 keV of the nearest radio galaxy, Centaurus A (Cen A). The accretion geometry around the central engine in Cen A is still debated, and we investigate possible configurations using ... More