Name: Radio 2017
Start: 2017-10-05T08:30:00+02:00
End: 2017-10-06T17:00:00+02:00
Location: Würzburg, Festung Marienberg

Thursday, October 5
- Thu, Oct 5
- Fri, Oct 6
- Registration Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
  
  Registration and Coffee upon arrival
  
  Conveners: Mrs Karin Kuhns (Universität Würzburg), Mrs Katharina Leiter
- GLOW: Consortium Member Meeting Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
  
  Scientific highlights
  
  Convener: Prof. Marcus Chair: Brüggen (Hamburger Sternwarte)
  - 1
    
    Welcome
    
    Speaker: Prof. Karl Mannheim (Universitaet Wuerzburg, Germany)
  - 2
    
    Chair Reports (GLOW/EC, LofarWG, GLOWSKA, ScienceWG)
    
    Speakers: Benedetta Ciardi, Dominik Schwarz, Karl Mannheim, Marcus Brüggen
  - 3
    
    New Member HTW Berlin
    
    Speaker: Hermann Heßling
  - 4
    
    Report Denkschrift
    
    Speaker: Marcus Brüggen
    
    Slides
  - 5
    
    Report community paper "Radio Facilities"
    
    Speaker: Eduardo Ros
  - 6
    
    GLOW Web Refresh
    
    Speakers: Jörn Künsemöller, Matthias Hoeft
- 11:00 AM
  
  Coffee Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
- Science symposium: "Radio astronomy in the multi-frequency era", part I Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
  
  Convener: Matthias Chair: Kadler
  - 7
    
    Pulsar science with the German LOFAR stations
    
    The International LOFAR stations in Germany are mainly dedicated to pulsar observations. An unprecedented pulsar monitoring campaign has been carried out since 2013, thus enabling a variety of research topics. Such topics are mainly focused on interstellar medium (ISM) studies, and range from variations in the ISM electron content to Solar wind probing. I will describe this unique and cutting-edge data set, revise the works done by now and report the latest results from Bielefeld University and MPIfR.
    
    Speaker: Dr Caterina Tiburzi (MPIfR/Universitaet Bielefeld)
  - 8
    
    LOFAR observations of the quiet solar corona
    
    The solar corona is the hot, tenuous outer atmosphere of the Sun. It is highly structured due to coronal magnetic fields, but generally shows a barometric density profile along magnetic fields, for altitudes well below the sonic critical point that marks the transition towards the supersonic solar wind. If the Sun is observed at a given radio frequency, then the corona becomes opaque below the density level where that frequency corresponds to the local plasma frequency, that is a function of electron density only. LOFAR's frequency range corresponds to the middle (high band) and upper (low band) corona. Since the refractive index of a plasma approaches zero for radio waves near the local plasma frequency, refraction effects are important. A ray path through the solar corona shows total reflectance and cannot connect a source that is located near the solar limb and at such a coronal height, where the wave frequency equals the local plasma frequency, with an observer on Earth. This has important consequences on the appearance of the low-frequency radio Sun under quiet conditions. The diameter of the radio Sun increases with decreasing frequency, as expected from the relationship between electron density and plasma frequency. But it does not appear as a disk with constant brightness temperature, even for an isothermal corona. So deriving the radius of the radio Sun requires fitting of observed intensity profiles to ray-tracing simulations, based on free-free radio wave emission and absorption, as well as refraction. These simulations also depend on the plasma conditions above that radius. LOFAR's capability of simultaneously observing a broad frequency range enables the derivation of a consistent coronal density model. We'll present results for polar coronal density and temperature profiles based on LOFAR low band images.
    
    Speaker: Dr Christian Vocks (Leibniz-Institut für Astrophysik Potsdam)
    
    Slides
  - 9
    
    The low-frequency radio continuum—star formation rate relation in nearby galaxies with LOFAR
    
    We present first results of our survey of nearby galaxies with 140-MHz data from pointed observations and from the LOFAR 2-m Sky Survey (LoTSS). With the facet calibration technique we are now able to reach an rms noise level close to the thermal noise of ~150 µJy/beam at 7—10 arcsec spatial resolution. These maps are sensitivity matched with medium-deep (1 hr) observations of other state-of-the-art radio interferometers such as the Jansky VLA. We have selected our galaxies from the SINGS and KINGFISH infrared surveys, which provide us with ample of ancillary data. The infrared maps from HERSCHEL and Spitzer can be combined with GALEX far-ultraviolet maps in order to construct reliable star-formation rate surface density maps, corrected for internal absorption by dust. Balmer Halpha maps can be used to separate the thermal radio continuum emission, although at 140 MHz we expect the thermal fraction to be small (< 10 per cent). We also have ancillary radio maps, both 1.4-GHz continuum maps from the WSRT SINGS survey, as well as HI line emission maps from the VLA THINGS survey. We also have selected some highly inclined (>80 degree) galaxies from the CHANG-ES survey with complementary Jansky VLA data at 1.5 and 6 GHz. These data can be used to study the spatially resolved radio continuum—star formation rate (RC—SFR) relation on a 1-kpc scale in a statically meaningful sample. As part of this study, we will explore the effects of cosmic-ray transport by diffusion in galactic discs, the relation between the magnetic field and gas density as well as gas kinematics and the vertical cosmic ray transport by advection in galactic winds.
    
    Speaker: Dr Volker Heesen (Univ. of Hamburg)
  - 10
    
    LOFAR observations of the distant blazar S5 0836+710
    
    Speaker: Alexander Kappes
  - 11
    
    Progress Report: LOFAR observation of NGC 4631
    
    I will present the current status of the main part of my PhD project, the LOFAR observation of NGC 4631. NGC 4631 is a large edge-on spiral galaxy with high star formation rate and strongly interacts with NGC 4627 and NGC 4656/7. NGC 4631 also exhibits a large, prominent halo of warm and hot ionized gas. NGC 4631 has been observed as part of the LOFAR Survey of nearby galaxies with the LOFAR HBA for 6.4 hours during Cycle 0 (2013-04-18/19), using the Core and Remote Stations. This talk covers improvements of direction-dependent over direction-independent calibration, experimentation with Factor parameters and facet setups and first glance analysis of the current processing stage image. The LOFAR image of NGC 4631 shows lots of diffuse emission outside the disk, correlating nicely with previous X-ray and radio observations. Furthermore, due to the huge improvement in resolution over previous measurements, fine structures are discernible in the halo, e.g. filaments can be traced up to 10 kpc out of the disk. The talk may also include a quick look at NGC 4656, one of NGC 4631's interaction partners which is also in the field of view of another facet of the observation.
    
    Speaker: Mr Stefan Blex (AIRUB)
    
    Slides
  - 12
    
    Deep L-band VLA observations of the Toothbrush cluster
    
    We present the results of deep L-band VLA observations of the merging galaxy cluster 1RXS J0603.3+4214, which host one of the brightest relics, known as Toothbrush, and an elongated giant radio halo. Our new VLA images provide an unprecedented detailed view of the Toothbrush, revealing enigmatic filamentary structures. These VLA observations in combination with GMRT and LOFAR data, allowed us to study the spectral index distribution at very high resolution. A simple toy model suggest that there are significant variations of the magnetic field strength along the line of sight. The downstream spectral profile, between 150 MHz to 1.5 GHz, can be explained by an inhomogeneous magnetic field and high Mach number shock. The radio halo shows an average spectral index of about $\alpha=-1.16\pm0.05$ and a slight gradient from north to south. Excluding the southernmost part, the halo morphology agrees very well with the X-ray morphology. A power-law correlation is found between the radio and X-ray surface brightness. We will also present our preliminary polarization results.
    
    Speaker: Ms Kamlesh Rajpurohit (Thüringer Landessternwarte Tautenburg)
    
    Slides
- 1:00 PM
  
  Lunch Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
- Science symposium: "Radio astronomy in the multi-frequency survey era", part II Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
  
  Convener: Joe Chair: Mohr
  - 13
    
    Faraday rotation at low frequencies
    
    I will present a low-frequency, broadband polarisation study of the FRII radio galaxy PKS J0636−2034 (z = 0.0551), using data from the Murchison Widefield Array (MWA) from 70 to 230 MHz. The large, continuous wavelength-squared coverage across the MWA band allows the polarisation and Faraday rotation properties to be determined with a precision approximately two orders of magnitude better than traditional cm-wavelength radio interferometers. A combination of rotation measure synthesis and broadband polarisation model-fitting are used to constrain the Faraday depolarisation properties of the source to very high accuracy.
    
    Speaker: Shane O'Sullivan (Hamburg)
  - 14
    
    High Frequency Cluster Radio Galaxies: Luminosity Functions and Implications for SZE Selected Cluster Samples
    
    We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the Meta-Catalog of X-ray detected Clusters of galaxies (MCXC; $\langle z \rangle = 0.14$) at South Pole Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220~GHz are extracted from the 2500~deg$^2$ SPT-SZ survey maps at the locations of SUMSS sources, producing a multi-frequency catalog of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150~GHz are biased low by the cluster Sunyaev-Zel'dovich Effect (SZE) signal, which is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogs. We find that the high frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843~MHz. We use the 150~GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass-observable relation. If we assume there is no redshift evolution in the radio galaxy LF then $1.8\pm0.7$~percent of the clusters with detection significance $\xi \geq 4.5$ would be lost from the sample. Allowing for redshift evolution of the form $(1+z)^{2.5}$ increases the incompleteness to $5.6\pm1.0$~percent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.
    
    Speaker: Mr Gupta Nikhel (LMU, Munich)
  - 15
    
    Broadband Polarization Sky Survey with the MPIfR-MT-SKA prototype dish
    
    I will discuss about the future prospects of the MeerKAT prototype single-dish for performing broadband all sky polarization survey.
    
    Speaker: Dr ARITRA BASU (Max Planck Institute for Radio Astronomy)
    
    Slides
  - 16
    
    Enabling S-Band Capability for MeerKAT
    
    This talk will be on the MPIfR's efforts to equip the MeerKAT array with receivers and signal processing infrastructure that allows access to the skies in the 1750-3500 MHz range. We are building a 400-beam GPU-based beam-former and a processing cluster to serve as the pulsar and transient hunting machine. The plans on this machine and results from the initial tests with two telescopes will be discussed.
    
    Speaker: Dr Ramesh Karuppusamy (MPIfR)
  - 17
    
    Merging galaxy clusters in radio surveys
    
    The intra-cluster medium accounts for most of the baryon mass in galaxy clusters. However, its dynamical processes, magnetic fields properties, and cosmic ray content are still poorly constrained. Diffuse synchrotron emission in galaxy clusters provides a probe for all of these three components. Radio relics are synchrotron emission sites found in downstream regions of galaxy cluster merger shocks. While they are often confirmed through targeted X-ray and radio observations their signature is also present in large surveys. Several models for the origin of radio relics have been proposed. Through Bayesian statistics one can infer the posterior likelihood of competing models given the data and prior information. Approximate Bayesian Computation (ABC) is an approach to estimate the posterior likelihood if the complexity of the data is high. We use ABC to investigate diffusive shock acceleration models with and without pre-existing relativistic electrons based on the NVSS survey and cosmological simulations. I present what we can infer from our current data pool and which surveys we need to strengthen the model inference capabilities of our ABC approach.
    
    Speaker: Mr Jakob Gelszinnis (Thüringer Landessternwarte)
    
    Slides
  - 18
    
    Properties of Main Sequence star-forming galaxies before and after MIGHTEE
    
    I will describe what we've learned in the last decade about star-forming galaxies by using the deepest available HST, Spitzer, Herschel, ALMA and JVLA data and how this is going to be boosted and refined in the coming years thanks to the new upcoming radio continuum facilities like MeerKAT and eventually SKA. I'll focus in particular on the MIGHTEE/LADUMA surveys and the still closed windows they are going to open on galaxy evolution studies.
    
    Speaker: Dr Maurilio Pannella (LMU München)
    
    Slides
- 3:30 PM
  
  Coffee Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
- Science symposium: Science Symposium "Radio astronomy in the multifrequency era", part III Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  Convener: Jörn Chair: Wilms
  - 19
    
    Radio and CTA: Synergies and Transients
    
    CTA will be the first Cerenkov Facility designed for observatory operation. This will facilitate multifrequency studies of stationary, variable, and transient sources. The radio- and VHE gamma-ray sky are dominated by non-thermal sources and joint studies in both bands will provide matching constraints on source properties and radiation mechanisms. Properties and construction time-scales of the two stations operating 120 telescopes as well as modes of operation and access will be described.
    
    Speaker: Prof. Stefan Wagner (LSW)
  - 20
    
    Multi-Wavelength Source Identification using Machine Learning Methods
    
    Driven by a wealth of upcoming missions and observatories across a wide frequency range, astronomy is entering a new era of survey science. As data volumes grow rapidly and data structures become more heterogeneous, progress regarding source populations will still crucially depend from efficient identification of sources across these multi-frequency and multi-messenger datasets. In recent years, machine learning approaches have matured into a powerful research tool for automatic source classification. In this talk, chances and challenges of machine learning methods as used already for gamma-ray observations will be discussed in the context of upcoming large radio surveys.
    
    Speaker: Dominik Elsaesser (TU Dortmund)
  - 21
    
    Imaging the spatial, spectral, and temporal sky via information field theory
    
    Information field theory (IFT), the information theory for fields, permits the derivation of imaging algorithms, which are optimized for specific measurement situations. I will present the current state of the IFT algorithms RESOLVE and D3PO for radio synthesis and $\gamma$/X-ray imaging, respectively, highlight scientific results obtained with them, and discuss their future evolution.
    
    Speaker: Dr Torsten Enßlin (MPI for Astrophysics)
    
    Slides
  - 22
    
    Active Galactic Nuclei Jets Probed by Very-Long-Baseline Interferometry
    
    Very-long-baseline interferometry (VLBI) probes compact regions at the hearts of active galactic nuclei at a submilliarcsecond resolution. This technique enables detailed studies to be made of the non-thermal emission in the innermost regions of relativistic plasma jets. The scope of VLBI studies becomes ever broader, reaching higher resolution with longer baselines (space VLBI) and at higher frequencies (millimetre wavelength VLBI), opening new horizons with high fidelity polarization imaging to study the magnetic field structure and Faraday rotation, and exploring ample synergies in astrometric studies provided by the first results coming from the GAIA mission. Over the past decade, the combination of VLBI observations and the multi-messenger approach have proven exceptionally successful, helping to understand the nature of non-thermal gamma-ray emission observed with the Fermi/LAT, providing valuable insight on the physics of relativistic X-ray iron lines in AGN, searching for the astrophysical sources of neutrinos detected by IceCube, and potentially expanding this type of studies to the search of electromagnetic counterparts of gravitational waves. I will summarize recent results from some of these topics.
    
    Speaker: Prof. Eduardo Ros (MPI für Radioastronomie & Univ. de València)
  - 23
    
    Deciphering the 3D Morphology of Blazars with GMRT observations
    
    Speaker: Paul Ray Burd
    
    Slides
  - 24
    
    Multi-frequency estimation of the cosmic radio dipole from continuum radio surveys
    
    Continuum surveys of the radio sky provide a rich resource of information. Besides the analysis of individual galaxies and other astrophysical sources, they also allow us to probe cosmological models. We analyse the data provided by several surveys across radio frequencies to estimate the Cosmic Radio Dipole in the radio source counts. This dipole is a deviation from the statistically isotropic Universe caused by the proper motion of the Solar system and the large scale structure. The kinetic effect is also hold responsible for the temperature dipole of the Cosmic Microwave Background. In this talk I will describe the quality cuts required to make radio continuum catalogues suitable for cosmological analysis. In particular I will show results from the analysis of NVSS, SUMSS, WENSS, TGSS ADR1 and GLEAM, which together cover a decade in frequency and the full sky.
    
    Speaker: Mr Thilo Siewert (Bielefeld University)
    
    Slides
  - 25
    
    VLBI and gamma-ray studies of radio galaxies
    
    The γ-ray sky is strongly dominated by blazars, i.e. AGN with relativistic jets oriented closely with our line of sight. Radio galaxies are their misaligned counterparts, and make up about ∼ 1-2% of all AGN observed by Fermi-LAT. At TeV energies, only 5 radio galaxies have currently been detected, but recent work has shown that the CTA has good potential for detecting more of these elusive Very-High-Energy sources. In spite of their small numbers in $\gamma$-ray catalogs, radio galaxies provide us with a view of AGN jets which is less biased by Doppler boosting effects, and allow us to test jet production and emission models in light of the unified scheme of radio-loud AGN. The combination of γ-ray data and high-resolution Very Long Baseline Interferometry (VLBI) studies is a powerful tool in order to investigate these objects. We present selected results of an ongoing study focused on the radio galaxies in the southern-hemisphere VLBI (and multi-wavelength) monitoring program TANAMI.
    
    Speaker: Mr Roberto Angioni (Max-Planck Institut für Radioastronomie)
    
    Slides
- Dinner: Barbecue at Observatory (Bus transfer) Hans-Haffner Sternwarte Hettstadt
  
  Hans-Haffner Sternwarte Hettstadt
Friday, October 6
- Thu, Oct 5
- Fri, Oct 6
- GLOW: LOFAR Working Group I Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
  - 26
    
    Reports from LOFAR station owners
  - 27
    
    Report KSP representatives
    
    Speaker: Marcus, Ralf-Jürgen, Benedetta, Christian, Catarina/Joris/Jochen
  - 28
    
    Report ILT Board
    
    Speaker: Dominik
  - 29
    
    LOFAR 2.0 current plans, incl. discussion
    
    Speaker: Dominik
  - 30
    
    Report LOFAR4SW (Horizon2020)
    
    Speaker: Catarina
  - 31
    
    Network operations
    
    Speaker: Thomas on behalf of Olaf
- 10:30 AM
  
  Coffee Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
- GLOW: LOFAR Working Group II Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
  - 32
    
    GLOW mode
    
    Speaker: Olaf/Jörn
    
    Slides
  - 33
    
    Jülich LTA
    
    Speaker: Oleg Tsigenov
  - 34
    
    Jureca Computing
    
    Speaker: Matthias
  - 35
    
    Imaging software
    
    Speaker: David
  - 36
    
    GLOW in-kind
    
    Speaker: Dominik
  - 37
    
    Discussion. e.g. GLOW Mode acknowledgement
    
    Speaker: All
- 12:30 PM
  
  Lunch Ritterstube (Burggasstätten)
  
  Ritterstube
  
  Burggasstätten
- GLOW: SKA Working Group I Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
  - 38
    
    The D-MeerKAT project, quick overview
    
    Speaker: Dominik Schwarz
  - 39
    
    Report from MIGHTEE meeting
    
    Speaker: Maurillio Panella
    
    Slides
  - 40
    
    Update MeerKAT
    
    I will provide an update on the current status of the MeerKAT array.
    
    Speaker: Hans-Rainer Klöckner (Max-Planck-Institut für Radioastronomie)
  - 41
    
    Report Aeneas, consequences for german SKA data centers
    
    Speaker: Hans-Rainer Klöckner
  - 42
    
    Status SKA and German involvement after Wahl 2017
    
    Speaker: Prof. Karl Mannheim (Universitaet Wuerzburg, Germany)
    
    Slides
  - 43
    
    Diskussion: MoU GLOW-SKA SA zu MeerKAT
    
    Speaker: All
  - 44
    
    Meeting Summary
    
    Speaker: Marcus Brüggen
- 3:30 PM
  
  Coffee Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").
- 4:00 PM
  
  End of the Meeting Room Egloffstein
  
  Room Egloffstein
  
  Würzburg, Festung Marienberg
  
  The meeting takes place in the historic building of Fortress Marienberg. You can easily get their by bus (#9), car (chargeable parking lot), or by foot from "Alte Mainbrücke" (via "Tellsteige").

Radio 2017

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Hans-Haffner Sternwarte Hettstadt

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Ritterstube

Burggasstätten

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg

Room Egloffstein

Würzburg, Festung Marienberg