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Paragi Z.,Joint Institute for VLBI in Europe | Frey S.,FOMI Satellite Geodetic Observatory | Kaaret P.,University of Iowa | Cseh D.,Radboud University Nijmegen | And 2 more authors.
Astrophysical Journal | Year: 2014

Recently, Nyland et al. argued that the radio emission observed in the center of the dwarf galaxy NGC 404 originates in a low-luminosity active galactic nucleus powered by a massive black hole (MBH, M ≲ 106 M ⊙). High-resolution radio detections of MBHs are rare. Here we present sensitive, contemporaneous Chandra X-ray, and very long baseline interferometry (VLBI) radio observations with the European VLBI Network. The source is detected in the X-rays, and shows no long-term variability. If the hard X-ray source is powered by accretion, the apparent low accretion efficiency would be consistent with a black hole (BH) in the hard state. Hard state BHs are known to show radio emission compact on the milliarcsecond scales. However, the central region of NGC 404 is resolved out on 10 mas (0.15-1.5 pc) scales. Our VLBI non-detection of a compact, partially self-absorbed radio core in NGC 404 implies that either the BH mass is smaller than M ⊙, or the source does not follow the fundamental plane of BH activity relation. An alternative explanation is that the central BH is not in the hard state. The radio emission observed on arcsecond (tens of parsecs) scales may originate in nuclear star formation or extended emission due to AGN activity, although the latter would not be typical considering the structural properties of low-ionization nuclear emission-line region galaxies with confirmed nuclear activity. © 2014. The American Astronomical Society. All rights reserved. Source

Braunmuller P.,FOMI Satellite Geodetic Observatory | Orosz G.,Budapest University of Technology and Economics
Geocarto International | Year: 2013

Nowadays, one of the most widespread surface monitoring techniques is synthetic aperture radar interferometry (InSAR), which can be used to measure millimetre-scale deformations by comparing the phase information of satellite images taken a few days to a few years apart. To attain this precision, we need methods that use dozens of radar images and rely on accurate additional information (e.g. satellite positions and meteorological data). There are several limiting spatial and meteorological factors which should be taken into consideration when doing high-precision deformation analysis. Also, due to the relatively high price of these products, a cost optimization is essential before purchasing by taking the above-mentioned aspects into consideration. Here, we give an overview of a new nationwide database intended for this purpose. The paper also summarizes the major advancements and the on-going research done in Hungary in the field of radar interferometry. © 2013 Copyright Taylor and Francis Group, LLC. Source

Frey S.,FOMI Satellite Geodetic Observatory | Paragi Z.,Joint Institute for VLBI in Europe | An T.,Chinese Academy of Sciences | An T.,Netherlands Institute for Radio Astronomy | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

The radio-emitting quasar SDSS J1425+3231 (z = 0.478) was recently found to have double-peaked narrow [Oiii] optical emission lines. Based on the analysis of the optical spectrum, Peng et al. suggested that this object harbours a dual active galactic nucleus (AGN) system, with two supermassive black holes (SMBHs) separated on a kpc scale. SMBH pairs should be ubiquitous according to hierarchical galaxy formation scenarios in which the host galaxies and their central black holes grow together via interactions and eventual mergers. Yet the number of presently confirmed dual SMBHs on kpc or smaller scales remains small. A possible way to obtain direct observational evidence for duality is to conduct high-resolution radio interferometric measurements, provided that both AGN are in an evolutionary phase when some activity is going on in the radio. We used the technique of very long baseline interferometry (VLBI) to image SDSS J1425+3231. Observations made with the European VLBI Network at 1.7- and 5-GHz frequencies in 2011 revealed compact radio emission at sub-mJy flux density levels from two components with a projected linear separation of ∼2.6kpc. These two components support the possibility of a dual AGN system. The weaker component remained undetected at 5 GHz due to its steep radio spectrum. Further study will be necessary to securely rule out a jet-shock interpretation of the less dominant compact radio source. Assuming the dual AGN interpretation, we discuss black hole masses, luminosities and accretion rates of the two components using available X-ray, optical and radio data. While high-resolution radio interferometric imaging is not an efficient technique to search blindly for dual AGN, it is an invaluable tool to confirm the existence of selected candidates. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS. Source

Gabanyi K.E.,University of Szeged | Gabanyi K.E.,Research Center for Astronomy and Earth science | Frey S.,FOMI Satellite Geodetic Observatory | Xiao T.,Chinese Academy of Sciences | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The Seyfert galaxy NGC 5515 has double-peaked narrow-line emission in its optical spectrum, and it has been suggested that this could indicate that it has two active nuclei. We observed the source with high-resolution very long baseline interferometry at two radio frequencies, reduced archival Very Large Array data, and re-analysed its optical spectrum. We detected a single, compact radio source at the position of NGC 5515, with no additional radio emission in its vicinity. The optical spectrum of the source shows that the blue and red components of the double-peaked lines have very similar characteristics. While we cannot rule out unambiguously thatNGC5515 harbours a dualAGN, the assumption of a singleAGNprovides amore plausible explanation for the radio observations and the optical spectrum. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Bruyninx C.,Royal Observatory of Belgium | Habrich H.,Bundesamt fur Kartographie und Geodasie | Sohne W.,Bundesamt fur Kartographie und Geodasie | Kenyeres A.,FOMI Satellite Geodetic Observatory | And 2 more authors.
International Association of Geodesy Symposia | Year: 2012

This paper describes the EUREF Permanent Network (EPN) and the efforts made to monitor and improve the quality of the EPN products and services. It is shown that the EPN is becoming a multi-GNSS tracking network and that the EPN Central Bureau and the Analysis Centers are preparating to include the new satellite signals in their routine operations. Thanks to the EPN Special Project on "Reprocessing", set up early 2009, EPN products with much better quality and homogeneity will be generated. The Special Project on "Real-time analysis" will improve the reliability of the EPN real-time data streams and develop new EPN real-time products. © Springer-Verlag Berlin Heidelberg 2012. Source

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