F. Sweijen

TL;DR: In this paper, the authors present a complete survey of the Long-Baseline Calibrator Survey (LBCS) data, which consists of 30006 observations of 24713 sources in the northern sky, selected for a combination of high low-frequency radio flux density and flat spectral index using existing surveys.

Abstract: The prominent radio source Hercules A features complex structures in its radio lobes. Although it is one of the most comprehensively studied sources in the radio sky, the origin of the ring structures in the Hercules A radio lobes remains an open question. We present the first sub-arcsecond angular resolution images at low frequencies (<300 MHz) of Hercules A, made with the International LOFAR Telescope. With the addition of data from the Karl G. Jansky Very Large Array, we mapped the structure of the lobes from 144 MHz to 7 GHz. We explore the origin of the rings within the lobes of Hercules A, and test whether their properties are best described by a shock model, where shock waves are produced by the jet propagating in the radio lobe, or by an inner-lobe model, where the rings are formed by decelerated jetted plasma. From spectral index mapping our large frequency coverage reveals that the curvature of the different ring spectra increases with distance away from the central active galactic nucleus. We demonstrate that the spectral shape of the rings is consistent with synchrotron aging, which speaks in favor of an inner-lobe model where the rings are formed from the deposition of material from past periods of intermittent core activity.

TL;DR: In this article, the authors used the International LOFAR telescope (ILT) to study the radio galaxy 3C 293, which has long been thought to be a restarted galaxy on the basis of its radio morphology.

TL;DR: In this article, the International LOFAR Telescope (ILT) was used for sub-arcsecond imaging of 6 radio sources at frequencies down to 30 MHz, which is more than an order of magnitude better resolution than pre-ILT observations at similar frequencies.