J. Anton Zensus

Max Planck Institute for Radio Astronomy | MPIFR · Division of Radio Astronomy/Very Long Baseline Radiointerferometry

Total intensity variability light curves offer a unique insight into the ongoing debate about the launching mechanism of jets. For this work, we utilised the availability of radio and γ -ray light curves over a few decades of the radio source 3C 84 ( NGC 1275 ). We calculated the multi-band time-lags between the flares identified in the light curve...

Total intensity variability light curves offer a unique insight into the ongoing debate about the launching mechanism of jets. For this work, we utilise the availability of radio and $\gamma$-ray light curves over a few decades of the radio source 3C 84 (NGC 1275). We calculate the multiband time lags between the flares identified in the light curv...

The LOPES experiment was a radio interferometer built at the existing air shower array KASCADE-Grande in Karlsruhe, Germany. The last configuration of LOPES was called LOPES 3D and consisted of ten tripole antennas. Each of these antennas consisted of three crossed dipoles east-west, north-south, and vertically aligned. With this, LOPES 3D had the...

Aims. Hot accretion flows are thought to be able to power the relativistic jets observed in active galactic nuclei. They can be presented as standard and normal evolution (SANE) disks or magnetically arrested disks (MAD) – two states that imply profound differences in the physical properties of the disks themselves and the outflows they produce. Me...

Aims. Hot accretion flows are thought to be able to power the relativistic jets observed in Active Galactic Nuclei. They can present themselves as SANE (Standard And Normal Evolution) disks or MAD (Magnetically Arrested Disks), two states implying profound differences in the physical properties of the disks themselves and of the outflows they produ...

3C 84 ( NGC 1275 ) is one of the brightest radio sources in the millimetre radio bands, which led to a plethora of very-long-baseline interferometry (VLBI) observations at numerous frequencies over the years. They reveal a two-sided jet structure, with an expanding but not well-collimated parsec-scale jet, pointing southward. High-resolution millim...

3C84 (NGC1275) is one of the brightest radio sources in the mm radio-bands, which led to a plethora of VLBI observations at numerous frequencies over the years. They reveal a two-sided jet structure, with an expanding but not well-collimated parsec-scale jet, pointing southward. High resolution mm-VLBI observations allow the study and imaging of th...

Symmetric achromatic variability (SAV) is a rare form of radio variability in blazars that has been attributed to gravitational milli-lensing by a ∼10 ² –10 ⁵ M ⊙ mass condensate. Four SAVs have been identified between 1980 and 2020 in the long-term radio monitoring data of the blazar PKS 1413 + 135. We show that all four can be fitted with the sam...

Context. In February 2017 the blazar OJ 287, one of the best super-massive binary-black-hole-system candidates, was detected for the first time at very high energies (VHEs; E > 100 GeV) with the ground-based γ -ray observatory VERITAS. Aims. Very high energy γ rays are thought to be produced in the near vicinity of the central engine in active gala...

In February 2017 the blazar OJ287, one of the best super-massive binary-black-hole-system candidates, was detected for the first time at very high energies (VHEs; E>100GeV) with the ground-based gamma-ray observatory VERITAS. Very high energy gamma rays are thought to be produced in the near vicinity of the central engine in active galactic nuclei....

Most large galaxies host supermassive black holes in their nuclei and are subject to mergers, which can produce a supermassive black hole binary (SMBHB), and hence periodic signatures due to orbital motion. We report unique periodic radio flux density variations in the blazar PKS 2131−021, which strongly suggest an SMBHB with an orbital separation...

Symmetric Achromatic Variability (SAV) is a rare form of radio variability in blazars that has been attributed to gravitational millilensing by a ~$10^2 - 10^5$ $M_\odot$ mass condensate. Four SAVs have been identified between 1980 and 2020 in the long-term radio monitoring data of the blazar PKS 1413+135. We show that all four can be fitted with t...

The collimation of relativistic jets launched from the vicinity of supermassive black holes (SMBHs) at the centers of active galactic nuclei (AGN) is one of the key questions to understand the nature of AGN jets. However, little is known about the detailed jet structure for AGN like quasars since very high angular resolutions are required to resolv...

Context. With the increase in the sensitivity and resolution of radio interferometry within recent years, the study of the collimation and acceleration region of extragalactic jets in active galactic nuclei (AGN) has come into focus. Whereas a large fraction of AGN jets show a change from parabolic to conical collimation profile around the Bondi ra...

With the increased sensitivity and resolution of radio interferometry the study of the collimation and acceleration region of jets in Active Galactic Nuclei (AGN) has come into focus within the last years. Whereas a large fraction of AGN jets reveal a change from parabolic to conical collimation around the Bondi radius, a small number of sources de...

We present RadioAstron space-VLBI observations of the nearby radio galaxy 3C 84 (NGC 1275) at the center of the Perseus Cluster. The observations were carried out during a perigee passage of the Spektr-R spacecraft on September 21-22, 2013 and involved a large global array of 24 ground radio telescopes observing at 5 GHz and 22 GHz together with th...

Jets which are powered by an AGN are a crucial element in the study of their central black holes (BH) and their immediate surroundings. The formation of such jets is the subject of intense research, mainly based on the dichotomy presented by the two main jet launching scenarios $-$ the one from Blandford & Payne (1982), and the one from Blandford &...

In nearby compact galaxy groups we can study the complex processes of galaxy interactions at high resolution and obtain a window into a time in the history of the Universe when the galaxies were closely spaced and the intergalactic medium was awash with gas. Stephan’s Quintet is a nearby compact galaxy group and a perfect laboratory for studying th...

Stephan's Quintet (SQ) is a nearby compact galaxy group and a perfect laboratory for studying the process of galaxy evolution through galaxy harassment and interaction. By analysing the kinematics of SQ we aim to provide an increased understanding of the group, the history of the interactions, their cause and effect, and the details regarding the p...

The Low-Frequency Array (LOFAR) Long-Baseline Calibrator Survey (LBCS) was conducted between 2014 and 2019 in order to obtain a set of suitable calibrators for the LOFAR array. In this paper we present the complete survey, building on the preliminary analysis published in 2016 which covered approximately half the survey area. The final catalogue co...

We present Space-VLBI RadioAstron observations at 1.6 GHz and 4.8 GHz of the flat spectrum radio quasar 3C 273, with detections on baselines up to 4.5 and 3.3 Earth Diameters, respectively. Achieving the best angular resolution at 1.6 GHz to date, we have imaged limb-brightening in the jet, not previously detected in this source. In contrast, at 4....

At optical wavelengths, blazar Electric Vector Position Angle (EVPA) rotations linked with gamma-ray activity have been the subject of intense interest and systematic investigation for over a decade. One difficulty in the interpretation of EVPA rotations is the inherent 180○ ambiguity in the measurements. It is therefore essential, when studying EV...

Dark Matter (DM) halos with masses below ∼108M⊙, which would help to discriminate between DM models, may be detected through their gravitational effect on distant sources. The same applies to primordial black holes, considered as an alternative scenario to DM particle models. However, there is still no evidence for the existence of such objects. Wi...

Dark Matter (DM) halos with masses below $\sim10^{8}$ $M_{\odot}$, which would help to discriminate between DM models, may be detected through their gravitational effect on distant sources. The same applies to primordial black holes, considered as an alternative scenario to DM particle models. However, there is still no evidence for the existence o...

Nearby radio galaxies that contain jets are extensively studied with very long baseline interferometry (VLBI), addressing jet launching and the physical mechanisms at play around massive black holes. 3C 84 is unique in this regard because the combination of its proximity and large super massive black hole mass provides a high spatial resolution to...

Nearby radio galaxies, containing jets, are extensively studied with VLBI, addressing jet launching and the physical mechanisms at play around massive black holes. 3C 84 is unique in this regard, because the combination of its proximity and large SMBH mass provides a high spatial resolution to resolve the complex structure at the jet base. For 3C 8...

At optical wavelengths, blazar Electric Vector Position Angle (EVPA) rotations linked with gamma-ray activity have been the subject of intense interest and systematic investigation for over a decade. One difficulty in the interpretation of EVPA rotations is the inherent 180{\deg} ambiguity in the measurements. It is therefore essential, when studyi...

At optical wavelengths, blazar Electric Vector Position Angle (EVPA) rotations linked with gamma-ray activity have been the subject of intense interest and systematic investigation for over a decade. One difficulty in the interpretation of EVPA rotations is the inherent 180° ambiguity in the measurements. It is therefore essential, when studying EV...

Context. Controversial studies on the jet collimation profile of BL Lacertae (BL Lac), the eponymous blazar of the BL Lac objects class, complicate the scenario in this already puzzling class of objects. Understanding the jet geometry in connection with the jet kinematics and the physical conditions in the surrounding medium is fundamental for bett...

Controversial studies on the jet collimation profile of BL Lacertae (BL Lac), the eponymous blazar of BL Lac objects class, complicate the scenario in this already puzzling class of objects. Understanding the jet geometry, in connection with the jet kinematics and the physical conditions in the surrounding medium, is fundamental to better constrain...

Context. Supermassive black holes in the centres of radio-loud active galactic nuclei (AGN) can produce collimated relativistic outflows (jets). Magnetic fields are thought to play a key role in the formation and collimation of these jets, but the details are much debated. Aims. We study the innermost jet morphology and magnetic field strength in t...

Context. Supermassive black holes in the centres of radio-loud active galactic nuclei (AGN) can produce collimated relativistic outflows (jets). Magnetic fields are thought to play a key role in the formation and collimation of these jets, but the details are much debated. Aims. We study the innermost jet morphology and magnetic field strength in t...

LOPES, the LOFAR prototype station, was an antenna array for cosmic-ray air showers operating from 2003 - 2013 within the KASCADE-Grande experiment. Meanwhile, the analysis is finished and the data of air-shower events measured by LOPES are available with open access in the KASCADE Cosmic Ray Data Center (KCDC). This article intends to provide a su...

LOPES, the LOFAR prototype station, was an antenna array for cosmic-ray air showers operating from 2003 to 2013 within the KASCADE-Grande experiment. Meanwhile, the analysis is finished and the data of air-shower events measured by LOPES are available with open access in the KASCADE Cosmic Ray Data Center (KCDC). This article intends to provide a s...

PKS 1413+135 is one of the most peculiar blazars known. Its strange properties led to the hypothesis almost four decades ago that it is gravitationally lensed by a mass concentration associated with an intervening galaxy. It exhibits symmetric achromatic variability, a rare form of variability that has been attributed to gravitational milli-lensing...

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 a 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 possibl...

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...

We present uniformly reprocessed and re-calibrated data from the RoboPol programme of optopolarimetric monitoring of active galactic nuclei (AGN), covering observations between 2013, when the instrument was commissioned, and 2017. In total, the dataset presented in this paper includes 5068 observations of 222 AGN with Dec > −25○. We describe the cu...

PKS 1413+135 is one of the most peculiar blazars known. Its strange properties led to the hypothesis almost four decades ago that it is gravitationally lensed by a mass concentration associated with an intervening galaxy. It exhibits symmetric achromatic variability, a rare form of variability that has been attributed to gravitational milli-lensing...

We present uniformly reprocessed and re-calibrated data from the RoboPol programme of optopolarimetric monitoring of active galactic nuclei (AGN), covering observations between 2013, when the instrument was commissioned, and 2017. In total, the dataset presented in this paper includes 5068 observations of 222 AGN with Dec > -25 deg. We describe the...

Sagittarius A* (Sgr A*) is the variable radio, near-infrared (NIR), and X-ray source associated with accretion onto the Galactic center black hole. We have analyzed a comprehensive submillimeter (including new observations simultaneous with NIR monitoring), NIR, and 2-8 keV dataset. Submillimeter variations tend to lag those in the NIR by $\sim$30...

Context. Flares in radio-loud active galactic nuclei are thought to be associated with the injection of fresh plasma into the compact jet base. Such flares are usually strongest and appear earlier at shorter radio wavelengths. Hence, very long baseline interferometry (VLBI) at millimeter(mm)-wavelengths is the best-suited technique for studying the...

Flares in radio-loud AGN are thought to be associated with the injection of fresh plasma into the compact jet base. Such flares are usually strongest and appear earlier at shorter radio wavelengths. Hence, VLBI at mm-wavelengths is best suited to study the earliest structural changes of compact jets associated with emission flares. We study the mor...

Following our study of the radio and high-energy properties of $\gamma$-ray-emitting radio galaxies, here we investigate the kinematic and spectral properties of the parsec-scale jets of radio galaxies that have not yet been detected by Fermi-LAT. We take advantage of the regular VLBI observations provided by the TANAMI monitoring program, and expl...

The "Space VLBI 2020: Science and Technology Futures" meeting was the second in The Future of High-Resolution Radio Interferometry in Space series. The first meeting (2018 September 5--6; Noordwijk, the Netherlands) focused on the full range of science applications possible for very long baseline interferometry (VLBI) with space-based antennas. Acc...

The "Space VLBI 2020: Science and Technology Futures" meeting was the second in The Future of High-Resolution Radio Interferometry in Space series. The first meeting (2018 September 5--6; Noordwijk, the Netherlands) focused on the full range of science applications possible for very long baseline interferometry (VLBI) with space-based antennas. Acc...

Aims. The γ-ray production mechanism and its localization in blazars are still a matter of debate. The main goal of this paper is to constrain the location of the high-energy emission in the blazar TXS 2013+370 and to study the physical and geometrical properties of the inner jet region on sub-pc scales. Methods. TXS 2013+370 was monitored during 2...

Aims. The γ -ray production mechanism and its localization in blazars are still a matter of debate. The main goal of this paper is to constrain the location of the high-energy emission in the blazar TXS 2013+370 and to study the physical and geometrical properties of the inner jet region on sub-pc scales. Methods. TXS 2013+370 was monitored during...

Context. Detailed studies of relativistic jets in active galactic nuclei (AGN) require high-fidelity imaging at the highest possible resolution. This can be achieved using very long baseline interferometry (VLBI) at radio frequencies, combining worldwide (global) VLBI arrays of radio telescopes with a space-borne antenna on board a satellite. Aims....

Detailed studies of relativistic jets in active galactic nuclei (AGN) require high-fidelity imaging at the highest possible resolution. This can be achieved using very long baseline interferometry (VLBI) at radio frequencies, combining worldwide (global) VLBI arrays of radio telescopes with a space-borne antenna on board a satellite. We present mul...

The $\gamma$-ray production mechanism and its localization in blazars are still a matter of debate. The main goal of this paper is to constrain the location of the high-energy emission in the blazar TXS 2013+370 and to study the physical and geometrical properties of the inner jet region on sub-pc scales. VLBI observations at 86 GHz and space-VLBI...

We present results of 3 mm observations of SiO maser sources in the Galactic Centre (GC) from observations with the Australia Telescope Compact Array between $2010-2014$, along the transitions of the SiO molecule at $v = 1, J = 2-1$ at 86.243 GHz and $v = 2, J = 2-1$ at 85.640 GHz. We also present the results of the 3 mm observations with Atacama L...

The largest Key Science Program of the RadioAstron space VLBI mission is a survey of active galactic nuclei (AGN). The main goal of the survey is to measure and study the brightness of AGN cores in order to better understand the physics of their emission while taking interstellar scattering into consideration. In this paper we present detection sta...

The largest Key Science Program of the RadioAstron space VLBI mission is a survey of active galactic nuclei (AGN). The main goal of the survey is to measure and study the brightness of AGN cores in order to better understand the physics of their emission while taking interstellar scattering into consideration. In this paper we present detection sta...

In the framework of the TANAMI multi-wavelength and VLBI monitoring, we study the evolution of the parsec-scale radio emission in radio galaxies in the southern hemisphere and their relationship to the $\gamma$-ray properties. In this first paper, we focus on Fermi-LAT-detected sources. We perform a kinematic analysis for five $\gamma$-ray detected...

Context. High-resolution very long baseline interferometry (VLBI) observations of NGC 1052 show a two sided jet with several regions of enhanced emission and a clear emission gap between the two jets. This gap shrinks with increasing frequency and vanishes around ν ∼ 43 GHz. The observed structures are due to both the macroscopic fluid dynamics int...

We present the design and performance of RoboPol, a four-channel optical polarimeter operating at the Skinakas Observatory in Crete, Greece. RoboPol is capable of measuring both relative linear Stokes parameters q and u (and the total intensity I) in one sky exposure. Though primarily used to measure the polarization of point sources in the R band,...

High-resolution Very-Long-Baseline Interferometry observations of NGC 1052 show a two sided jet with several regions of enhanced emission and a clear emission gap between the two jets.This gap shrinks with increasing frequency and vanishes around $\nu\sim43$ GHz. The observed structures are due to both the macroscopic fluid dynamics interacting wit...

We present the design and performance of RoboPol, a four-channel optical polarimeter operating at the Skinakas Observatory in Crete, Greece. RoboPol is capable of measuring both relative linear Stokes parameters $q$ and $u$ (and the total intensity $I$) in one sky exposure. Though primarily used to measure the polarization of point sources in the R...

Context . The advent of the Fermi gamma-ray space telescope with its superb sensitivity, energy range, and unprecedented capability to monitor the entire 4 π sky within less than 2–3 h, introduced a new standard in time domain gamma-ray astronomy. Among several breakthroughs, Fermi has – for the first time – made it possible to investigate, with hi...

We report results from a deep polarization imaging of the nearby radio galaxy 3C 84 (NGC 1275). The source was observed with the Global Millimeter VLBI Array (GMVA) at 86 GHz at an ultrahigh angular resolution of 50 μas (corresponding to ∼200Rs). We also add complementary multiwavelength data from the Very Long Baseline Array (VLBA; 15 and 43 GHz)...

The Galactic center supermassive black hole Sagittarius A* (Sgr A*) is one of the most promising targets to study the dynamics of black hole accretion and outflow via direct imaging with very long baseline interferometry (VLBI). At 3.5 mm (86 GHz), the emission from Sgr A* is resolvable with the Global Millimeter VLBI Array (GMVA). We present the f...

The Galactic Center supermassive black hole Sagittarius A* (Sgr A*) is one of the most promising targets to study the dynamics of black hole accretion and outflow via direct imaging with very long baseline interferometry (VLBI). At 3.5 mm (86 GHz), the emission from Sgr A* is resolvable with the Global Millimeter VLBI Array (GMVA). We present the f...

We report results from a deep polarization imaging of the nearby radio galaxy 3C$\,$84 (NGC$\,$1275). The source was observed with the Global Millimeter VLBI Array (GMVA) at 86$\,$GHz at an ultra-high angular resolution of $50\mu$as (corresponding to 250$R_{s}$). We also add complementary multi-wavelength data from the Very Long Baseline Array (VLB...

Context. Narrow-line Seyfert 1 galaxies (NLSy1s) constitute the active galactic nuclei subclass associated with systematically lower black hole masses. A few radio-loud NLSy1s have been detected in MeV-GeV energy bands by Fermi, and evidence that blazar-like jets are operating also in radio-loud NLSy1s, has been accumulated. Aims. We wish to quanti...

Aims. We present a multifrequency, dense radio monitoring program of the blazar OJ 287 using the 100-m Effelsberg 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,...

Context . Very long baseline interferometry (VLBI) observations at 86 GHz (wavelength, λ = 3 mm) reach a resolution of about 50 μ as, probing the collimation and acceleration regions of relativistic outflows in active galactic nuclei (AGN). The physical conditions in these regions can be studied by performing 86 GHz VLBI surveys of representative s...

We have monitored the R-band optical linear polarisation of ten jetted NLSy1 galaxies with the aim to quantify their variability and search for candidate long rotation of the polarisation plane. In all cases for which adequate datasets are available we observe significant variability of both the polarisation fraction and angle. In the best-sampled...