We present nine 3.6-cm VLBI observations of the optically violent variable (OVV) flat-spectrum radio quasar PKS 0420–014 taken over a period of three years (1989.32– 1992.48); we also show a VLBI map from observations at 43 GHz in 1992.4. We trace jet evolution and variability with individual components. We find superluminal motion with βapp ∼ 2–14c for five jet components. Components ejected m...

Throughout most of the history of radio interferometry studies of Active Galactic Nuclei (AGN) using VLBI, attempts to extract physically meaningful information from VLBI observations have been dominated by visibility-based approaches to analysis, such as model fitting of the self-calibrated visibility data. This approach has been extremely valuable in multi-epoch studies of superluminal motion...

At present spacecraft angular position with the Deep Space Network (DSN) is determined using group delay estimates from very long baseline interferometry (VLBI) phase measurements employing differential one-way ranging (DOR) tones. Group delay measurements require high signal-to-noise ratio (SNR) to provide modest angular position accuracy. On the other hand, VLBI phases with modest SNR can be ...

Millimeter very long baseline interferometry (mm-VLBI) provides the novel capacity to probe the emission region of a handful of supermassive black holes on sub-horizon scales. For Sagittarius A∗ (Sgr A∗), the supermassive black hole at the center of the Milky Way, this provides access to the region in the immediate vicinity of the horizon. Broderick et al. have already shown that by leveraging ...

Sagittarius A* is the source of near infrared, X-ray, radio, and (sub)millimeter emission associated with the supermassive black hole at the Galactic Center. In the submillimeter regime, Sgr A* exhibits time-variable linear polarization on timescales corresponding to <10 Schwarzschild radii of the presumed 4 × 106 M black hole. In previous work, we demonstrated the potential for total-intensity...

Abstract The Potsdam Open Source Radio Interferometry Tool (PORT) is the very long baseline interferometry (VLBI) analysis software developed and maintained at GFZ German Research Centre for Geosciences. Chiefly, PORT tasked with timely processing of VLBI sessions post-processing activities supporting generation celestial terrestrial reference frames. In addition, it serves as a framework resea...

We monitored 3C 273 with VLBI at 15–86 GHz since 1990. We discuss component trajectories, opacity effects, a rotating jet, and outburst-ejection relations from Gamma-ray to radio bands.

Very-long-baseline interferometry (VLBI) is a challenging observational technique, which requires in-depth knowledge about radio telescope instrumentation, interferometry, and the handling of noisy data. The reduction in raw data mostly left to scientists demands use complex algorithms implemented comprehensive software packages. correct application these necessitates good understanding underly...

We have obtained 8.4 GHz VLBA observations of a 31-GHz complete sample of ∼ 100 sources between 10 and 100 mJy. The main goals of these observations are: to determine the angular size, radio spectra and identification for a weak sample of high frequency sources; to find the fraction of sources which have sufficiently compact emission for use as calibrators for VLBI observations; and for design ...