Michael Bremer

A GLOBAL 86 GHZ VLBI SURVEY OF COMPACT RADIO SOURCES

We present results from a large 86 GHz global very long baseline interferometry (VLBI) survey of compact radio sources. The main goal of the survey is to increase by factors of 3-5 the total number of objects accessible for future 3 mm VLBI imaging. The survey observations reach a baseline sensitivity of 0.1 Jy and an image sensitivity of better than 10 mJy beam–1. A total of 127 compact radio sources have been observed. The observations have yielded images for 109 sources, extending the database of the sources imaged at 86 GHz with VLBI observation by a factor of 5, and only six sources have not been detected. The remaining 12 objects have been detected but could not be imaged due to insufficient closure phase information. Radio galaxies are less compact than quasars and BL Lac objects on the sub-milliarcsecond scale. The flux densities and sizes of the core and jet components of all imaged sources have been estimated using Gaussian model fitting. From these measurements, brightness temperatures have been calculated, taking into account the resolution limits of the data. The cores of 70% of the imaged sources are resolved. The core brightness temperatures of the sources peak at ~1011 K and only 1% have brightness temperatures higher than 1012 K. The cores of intraday variable (IDV) sources are smaller in angular size than those of non-IDV sources, and so yield higher brightness temperatures.

Superluminal non-ballistic jet swing in the quasar NRAO 150 revealed by mm-VLBI

Context. NRAO 150, a compact and bright radio to mm source showing core/jet structure, has been recently identified as a quasar at redshift

On the calibration of full-polarization 86 GHz global VLBI observations

z = 1.52

Improvement of the IRAM 30-m telescope from temperature measurements and finite-element calculations

through a near-IR spectral observation. Aims. To study the jet kinematics on the smallest accessible scales and to compute the first estimates of its basic physical properties. Methods. We have analysed the ultra-high-resolution images from a new monitoring program at 86 GHz and 43 GHz with the Global mm VLBI Array and the VLBA, respectively. An additional archival calibration VLBA data set, covering the period from 1997 to 2007, has been used. Results. Our data show an extreme projected counter-clockwise jet position angle swing at an angular rate of up to ≈ 11° yr within the inner

Thermal design and thermal behaviour of radio telescopes and their enclosures

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First 3 mm-VLBI imaging of the two-sided jet in Cygnus A - Zooming into the launching region

3 pc of the jet, which is associated with a non-ballistic superluminal motion of the jet within this region. Conclusions. The results suggest that the magnetic field could play an important role in the dynamics of the jet in NRAO 150, which is supported by the large values of the magnetic field strength obtained from our first estimates. The extreme characteristics of the jet swing make NRAO 150 a prime source to study the jet wobbling phenomenon.

FE model-based interpretation of telescope temperature variations

We report the development of a semi-automatic pipeline for the calibration of 86GHz full-polarization observations performed with the Global Millimeter-VLBI array (GMVA) and describe the calibration strategy followed in the data reduction. Our calibration pipeline involves non-standard procedures, since VLBI polarimetry at frequencies above 43GHz has not yet been well established. We also present, for the first time, a full-polarization global-VLBI image at 86GHz (source 3C 345), as an example of the final product of our calibration pipeline, and discuss the effect of instrumental limitations on the fidelity of the polarization images. Our calibration strategy is not exclusive to the GMVA, and could be applied to other VLBI arrays at millimeter wavelengths. The use of this pipeline will allow GMVA observers to obtain fully calibrated datasets shortly after the data correlation.

A highly magnetized twin-jet base pinpoints a supermassive black hole ?

Millimeter wavelength radio telescopes built in a conventional way from steel and aluminum require elaborate thermal control to guarantee small structural deformations and good observational performance. We describe the temperature monitoring system of the Institut de Radioastronomie Millime/spl acute/trique 30-m telescope and the use of temperature measurements in finite-element calculations of structural deformations. These calculations reproduce with good precision the measured thermal deformations of the telescope and allow the investigation and localization of thermally important elements in the telescope structure. The data are used for calculation of temperature induced main reflector surface deformations and of the associated actual beam pattern, and for prediction and real-time correction of the focus. The pointing cannot be fully predicted since the available finite-element model does not include the Nasmyth focus cabin (and the concrete pedestal). The long-term investigation of the telescopes thermal behavior led to an improvement of the thermal control system and to a better performance of the telescope.

No asymmetric outflows from Sagittarius A* during the pericenter passage of the gas cloud G2

Radio Astronomy and Radio Telescopes.- Radio Telescope Constructions in View of Thermal Aspects.- Telescope Enclosures.- The Variable Thermal Environment.- Calculation of Solar Illumination.- Temperature Measurements and FEM Thermal Deformation Calculations.- Heat Transfer.- Radiative Coupling towards Sky and Ground (External View Factor).- Measured Thermal Behaviour of Radio Telescopes.- Measured Thermal Behaviour of Enclosures.- Thermal Model Calculations.- Beam Formation and Beam Degradation.- Thermal Tolerances.- Optical Telescopes and Enclosures.- A Summary and Further Studies.

First 230? GHz VLBI fringes on 3C 279 using the APEX Telescope (Research Note)

Aims. We present for the first time Very Long Baseline Interferometry images of the radio galaxy Cygnus A at the frequency of 86 GHz. Thanks to the high spatial resolution of only 200 Schwarzschild radii (RS), such observations provide an extremely detailed view of the nuclear regions in this archetypal object and allow us to derive important constraints for theoretical models describing the launching of relativistic jets. Methods. A pixel-based analysis of the jet outflow, which still appears two-sided on the scales probed, was performed. By fitting Gaussian functions to the transverse intensity profiles, we could determine the jet width in the nuclear region. Results. The base of the jets appears wide. The minimum measured transverse width of (227 98) RS is significantly larger than the radius of the innermost stable circular orbit, suggesting that the outer accretion disk is contributing to the jet launching. The existence of a faster and Doppler de-boosted inner section, powered either from the rotation of the inner regions of the accretion disk or by the spinning black hole, is suggested by the kinematic properties and by the observed limb brightening of the flow.