Zsolt Paragi - Joint Institute for VLBI in Europe, Netherlands

Zsolt Paragi
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Zsolt Paragi
Joint Institute for VLBI in Europe, Netherlands

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High Energy Astrophysical Phenomena (21)
Astrophysics of Galaxies (17)
Cosmology and Nongalactic Astrophysics (16)
Instrumentation and Methods for Astrophysics (8)
Solar and Stellar Astrophysics (4)
Astrophysics (2)
Earth and Planetary Astrophysics (1)

Publications Authored By Zsolt Paragi

Radio-loud high-redshift quasars (HRQs), although only a few of them are known to date, are crucial for the studies of the growth of supermassive black holes (SMBHs) and the evolution of active galactic nuclei (AGN) at early cosmological epochs. Radio jets offer direct evidence of SMBHs, and their radio structures can be studied with the highest angular resolution using Very Long Baseline Interferometry (VLBI). Here we report on the observations of three HRQs (J0131-0321, J0906+6930, J1026+2542) at z>5 using the Korean VLBI Network and VLBI Exploration of Radio Astrometry Arrays (together known as KaVA) with the purpose of studying their pc-scale jet properties. Read More

Affiliations: 1Department of Astrophysics/IMAPP, Radboud University, Nijmegen, The Netherlands, 2Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, USA, 3Leiden Observatory, Leiden University, Leiden, The Netherlands, 4Department of Astrophysics/IMAPP, Radboud University, Nijmegen, The Netherlands, 5FÖMI Satellite Geodetic Observatory, Budapest, Hungary, 6Department of Astrophysics/IMAPP, Radboud University, Nijmegen, The Netherlands, 7Department of Astrophysics/IMAPP, Radboud University, Nijmegen, The Netherlands, 8School of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield, UK, 9Department of Astrophysics/IMAPP, Radboud University, Nijmegen, The Netherlands, 10Department of Astrophysics/IMAPP, Radboud University, Nijmegen, The Netherlands, 11Netherlands Institute for Radio Astronomy, 12Joint Institute for VLBI ERIC, Dwingeloo, The Netherlands, and, 13FÖMI Satellite Geodetic Observatory, Budapest, Hungary

High-redshift quasars are important to study galaxy and active galactic nuclei (AGN) evolution, test cosmological models, and study supermassive black hole growth. Optical searches for high-redshift sources have been very successful, but radio searches are not hampered by dust obscuration and should be more effective at finding sources at even higher redshifts. Identifying high-redshift sources based on radio data is, however, not trivial. Read More

Affiliations: 1McGill U., 2ASTRON, 3Cornell U., 4ASIAA, 5UC Berkeley, 6Cornell U., 7ASTRON, 8Columbia U., 9NRAO, WVU, 10NRAO, 11NRAO, 12ASTRON, API, 13McGill U., 14JPL, 15ASTRON, 16JIVE, 17WVU, 18JIVE, 19NRAO, 20DRAO, 21Arecibo, 22MPIfR, 23JIVE, Leiden, 24Cornell U.

The precise localization of the repeating fast radio burst (FRB 121102) has provided the first unambiguous association (chance coincidence probability $p\lesssim3\times10^{-4}$) of an FRB with an optical and persistent radio counterpart. We report on optical imaging and spectroscopy of the counterpart and find that it is an extended ($0.6^{\prime\prime}-0. Read More

I briefly review transient research with the EVN, with particular emphasis on the science that was (or is being) made possible with the latest real-time e-VLBI developments. Read More

According to optical stellar kinematics observations, an over-massive black hole candidate has been reported by van den Bosch et al. (2012) in the normal early-type galaxy NGC 1277. This galaxy is located in the central region of the Perseus cluster. Read More

We report the detection of the radio afterglow of a long gamma-ray burst (GRB) 111005A at 5-345 GHz, including the very long baseline interferometry observations with the positional error of 0.2 mas. The afterglow position is coincident with the disk of a galaxy ESO 580-49 at z= 0. Read More

We analyse Very Long Baseline Interferometry (VLBI) observations of the blazar CGRaBS J0809+5341 using Bayesian inference methods. The observation was carried out at 5 GHz using 8 telescopes that form part of the European VLBI Network. Imaging and deconvolution using traditional methods imply that the blazar is unresolved. Read More

Affiliations: 1Department of Astrophysics/IMAPP, Radboud University, The Netherlands, 2FÖMI Satellite Geodetic Observatory, Hungary, 3Department of Astrophysics/IMAPP, Radboud University, The Netherlands, 4Department of Astrophysics/IMAPP, Radboud University, The Netherlands, 5Joint Institute for VLBI ERIC, The Netherlands, 6Department of Astrophysics/IMAPP, Radboud University, The Netherlands, 7FÖMI Satellite Geodetic Observatory, Hungary, 8Joint Institute for VLBI ERIC, The Netherlands, 9Shanghai Astronomical Observatory, Chinese Academy of Sciences, P. R. China, 10Geoscience Australia, Australia

High-redshift radio-loud quasars are used to, among other things, test the predictions of cosmological models, set constraints on black hole growth in the early universe and understand galaxy evolution. Prior to this paper, 20 extragalactic radio sources at redshifts above 4.5 have been imaged with very long baseline interferometry (VLBI). Read More

Affiliations: 1XAO, China, 2OSO, Sweden, 3JIVE, Netherlands, 4XAO, China, 5SHAO, China, 6Universita degli Studi Roma Tre, Italy, 7KIAA, China, 8XAO, China, 9SHAO, China, 10SHAO, China

The X-ray source CXO J133815.6+043255 has counterparts in the UV, optical, and radio bands. Based on the multi-band investigations, it has been recently proposed by Kim et al. Read More

A bright optical flare was detected in the high-redshift ($z=2.133$) quasar CGRaBS J0809+5341 on 2014 April 13. The absolute magnitude of the object reached $-30. Read More

Affiliations: 1Department of Astrophysics/IMAPP, Radboud University Nijmegen, 2Department of Astrophysics/IMAPP, Radboud University Nijmegen, 3Department of Physics and Astronomy, The Johns Hopkins University, 4Department of Astrophysics/IMAPP, Radboud University Nijmegen, 5Leiden Observatory, Leiden University, 6Joint Institute for VLBI ERIC, 7Department of Astrophysics/IMAPP, Radboud University Nijmegen, 8School of Physics, Astronomy and Mathematics, University of Hertfordshire, 9FOMI Satellite Geodetic Observatory, 10Joint Institute for VLBI ERIC, 11Department of Astrophysics/IMAPP, Radboud University Nijmegen

Megahertz peaked-spectrum (MPS) sources have spectra that peak at frequencies below 1 GHz in the observer's frame and are believed to be radio-loud active galactic nuclei (AGN). We recently presented a new method to search for high-redshift AGN by identifying unusually compact MPS sources. In this paper, we present European VLBI Network (EVN) observations of 11 MPS sources which we use to determine their sizes and investigate the nature of the sources with ~10 mas resolution. Read More

Affiliations: 1U. Amsterdam, 2FOMI Observatory, 3ASTRON, 4NRL, 5IAFE/CONICET UBA, 6FOMI Observatory, 7IAFE/CONICET UBA, 8JIVE

HESS J1943+213 is an unidentified TeV source that is likely a high-frequency-peaked BL Lac (HBL) object but also compatible with a pulsar wind nebula (PWN) nature. Each of these enormously different astronomical interpretations is supported by some of the observed unusual characteristics. In order to finally classify and understand this object we took a three-pronged approach, through time-domain, high angular resolution, and multi-frequency radio studies. Read More

We present a multi-wavelength study of a newly discovered compact group (CG), SDSS J0959+1259, based data from XMM-Newton, SDSS and the Calar Alto optical imager BUSCA. With a maximum velocity offset of 500 km s$^{-1}$, a mean redshift of 0.035, and a mean spatial extension of 480 kpc, this CG is exceptional in having the highest concentration of nuclear activity in the local Universe, established with a sensitivity limit L$_{X}>4\times $10$^{40}$ erg s$^{-1}$ in 2--10 keV band and R-band magnitude $M_R < -19$. Read More

Affiliations: 1Oxford, 2Oxford, 3ICRAR/Curtin, 4IAPS/INAF Rome, 5Sydney, 6ASTRON, 7JIVE, 8Cornell

This chapter provides an overview of the possibilities for transient and variable-source astrophysics with the Square Kilometre Array. While subsequent chapters focus on the astrophysics of individual events, we focus on the broader picture, and how to maximise the science coming from the telescope. The SKA as currently designed will be a fantastic and ground-breaking facility for radio transient studies, but the scientifc yield will be dramatically increased by the addition of (i) near-real-time commensal searches of data streams for events, and (ii) on occasion, rapid robotic response to Target-of-Opprtunity style triggers. Read More

Affiliations: 1Onsala Space Observatory, Sweden, 2Joint Institute for VLBI in Europe, Netherlands, 3University of Manchester, UK, 4Michigan State University, USA, 5Michigan State University, USA

V959 Mon is a classical nova detected at GeV gamma-ray wavelengths on 2012 June 19. While classical novae are now routinely detected in gamma-rays, the origin of the shocks that produce relativistic particles has remained unknown. We carried out electronic European VLBI Network (e-EVN) observations that revealed a pair of compact synchrotron emission features in V959 Mon on 2012 Sep 18. Read More

Affiliations: 1University of Cape Town, 2Joint Institute for VLBI in Europe, 3University of Oxford, 4University of Cape Town, 5Square Kilometre Array South Africa, 6FÖMI Satellite Geodetic Observatory, 7CSIRO Astronomy and Space Science, 8Max-Planck-Institut für Radioastronomie

Galaxies and supermassive black holes (SMBHs) are believed to evolve through a process of hierarchical merging and accretion. Through this paradigm, multiple SMBH systems are expected to be relatively common in the Universe. However, to date there are poor observational constraints on multiple SMBHs systems with separations comparable to a SMBH gravitational sphere of influence (<< 1 kpc). Read More

Relativistic jets in active galactic nuclei (AGN) are among the most powerful astrophysical objects discovered to date. Indeed, jetted AGN studies have been considered a prominent science case for SKA, and were included in several different chapters of the previous SKA Science Book (Carilli & Rawlings 2004). Most of the fundamental questions about the physics of relativistic jets still remain unanswered, and await high-sensitivity radio instruments such as SKA to solve them. Read More


Adding VLBI capability to the SKA arrays will greatly broaden the science of the SKA, and is feasible within the current specifications. SKA-VLBI can be initially implemented by providing phased-array outputs for SKA1-MID and SKA1-SUR and using these extremely sensitive stations with other radio telescopes, and in SKA2 by realising a distributed configuration providing baselines up to thousands of km, merging it with existing VLBI networks. The motivation for and the possible realization of SKA-VLBI is described in this paper. Read More

Affiliations: 1INAF-Osservatorio Astronomico di Brera, Milano, 2University of Oxford, 3Instituto de Astrofisica de Canarias, 4Radboud University, Nijmegen, 5Università degli Studi di Cagliari, 6INAF-IRA Bologna, 7JIVE, Dwingeloo, 8INAF-Osservatorio Astronomico di Padova

A puzzling class of exotic objects, which have been known about for more than 30 years, is reaching a new era of understanding. We have discovered hundreds of Ultra Luminous X-ray sources (ULXs) - non-nuclear sources with X-ray luminosity in excess of the Eddington luminosity for "normal" size stellar Black Holes (BH) - and we are making progresses towards understanding their emission mechanisms. The current explanations imply either a peculiar state of accretion onto a stellar size BH or the presence of an intermediate mass BH, the long-sought link between stellar and supermassive BHs. Read More

The PSR J1023+0038 binary system hosts a neutron star and a low-mass, main-sequence-like star. It switches on year timescales between states as an eclipsing radio millisecond pulsar and a low-mass X-ray binary. We present a multi-wavelength observational campaign of PSR J1023+0038 in its most recent low-mass X-ray binary state. Read More

The vast collecting area of the Square Kilometre Array (SKA), harnessed by sensitive receivers, flexible digital electronics and increased computational capacity, could permit the most sensitive and exhaustive search for technologically-produced radio emission from advanced extraterrestrial intelligence (SETI) ever performed. For example, SKA1-MID will be capable of detecting a source roughly analogous to terrestrial high-power radars (e.g. Read More


We present here the results from dual-frequency phase-referenced VLBI observations of the Seyfert galaxy KISSR1494, which exhibits double peaked emission lines in its SDSS spectrum. We detect a single radio component at 1.6 GHz, but not at 5 GHz implying a spectral index steeper than $-1. Read More

Classical novae are the most common astrophysical thermonuclear explosions, occurring on the surfaces of white dwarf stars accreting gas from companions in binary star systems. Novae typically expel ~10^(-4) solar masses of material at velocities exceeding 1,000 kilometres per second. However, the mechanism of mass ejection in novae is poorly understood, and could be dominated by the impulsive flash of thermonuclear energy, prolonged optically thick winds, or binary interaction with the nova envelope. Read More

An international consortium is presently constructing a beamformer for the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile that will be available as a facility instrument. The beamformer will aggregate the entire collecting area of the array into a single, very large aperture. The extraordinary sensitivity of phased ALMA, combined with the extremely fine angular resolution available on baselines to the Northern Hemisphere, will enable transformational new very long baseline interferometry (VLBI) observations in Bands 6 and 7 (1. Read More

The energy released by an active galactic nucleus (AGN) has a strong impact on the surrounding interstellar medium (ISM). This feedback is considered to be the regulating factor for the growth of the central massive black hole, and for the rate of star formation in a galaxy. We have located, using Very Long Baseline Interferometry (VLBI), the fast outflow of neutral hydrogen in the young, restarted radio loud AGN 4C12. Read More

The black hole candidate, XTE J1752-223, was discovered in 2009 October when it entered an outburst. We obtained radio data from the Australia Telescope Compact Array for the duration of the ~9 month event. The lightcurves show that the radio emission from the compact jet persisted for the duration of an extended hard state and through the transition to the intermediate state. Read More

We present first results from electronic Multi-Element Remotely Linked Interferometer Network (e-MERLIN) and electronic European VLBI Network (e-EVN) observations of a small sample of ultra-steep spectrum radio sources, defined as those sources with a spectral index alpha < -1.4 between 74 MHz and 325 MHz, which are unresolved on arcsecond scales. Such sources are currently poorly understood and a number of theories as to their origin have been proposed in the literature. Read More

In the lead-up to the Square Kilometre Array (SKA) project, several next-generation radio telescopes and upgrades are already being built around the world. These include APERTIF (The Netherlands), ASKAP (Australia), eMERLIN (UK), VLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), Meerkat (South Africa), and the Murchison Widefield Array (MWA). Each of these new instruments has different strengths, and coordination of surveys between them can help maximise the science from each of them. Read More

Affiliations: 1JIVE, Netherlands, 2YNAO, P.R. China, 3YNAO, 4JIVE, 5JIVE, 6JIVE, 7SHAO, P.R. China, 8SHAO, 9SHAO

The X-ray transient MAXI J1836-194 is a newly-identified Galactic black hole binary candidate. As most X-ray transients, it was discovered at the beginning of an X-ray outburst. After the initial canonical X-ray hard state, the outburst evolved into a hard intermediate state and then went back to the hard state. Read More

The Arcminute Microkelvin Imager (AMI) is a telescope specifically designed for high sensitivity measurements of low-surface-brightness features at cm-wavelength and has unique, important capabilities. It consists of two interferometer arrays operating over 13.5-18 GHz that image structures on scales of 0. Read More

Results are presented from recent VLBI observations of Cygnus X-1 during X-ray spectral state changes. Using the EVN in e-VLBI mode and the VLBA with disk recording, we observed the X-ray binary at very high angular resolution and studied changes in the compact jets as the source made transitions from hard X-ray states to softer states. The radio light curves show that these transitions were accompanied by radio flaring events followed by a quenching of the radio emission, as expected from the current paradigm for disc-jet coupling in X-ray binaries. Read More

The high-redshift (z=4.72) blazar J1430+4204 produced an exceptional radio outburst in 2006. We analyzed 15-GHz radio interferometric images obtained with the Very Long Baseline Array (VLBA) before and after the outburst, to search for possible structural changes on milli-arcsecond angular scales and to determine physical parameters of the source. Read More


Some microquasars are permanently bright radio sources while others are faint but produce powerful radio outbursts. Most of the X-ray binaries (XRB) however are very faint or undetected in the radio regime. The European VLBI Network (EVN) recently introduced the Mark5 recording system which allows data rates of up to 1 Gbit/s. Read More

A radio "colour-colour" diagram is defined in order to determine the evolutionary state of synchrotron-emitting plasma bubbles that are ejected during outbursts in microquasars. We establish the colour-colour diagram for the plasmons of SS433 observed on 18 April 1998 using VLBI observations. We show that the radio plasmons are not consistent with a simple expanding sphere of plasmon. Read More