Pushing subarcsecond resolution imaging down to 30 MHz with the trans-European International LOFAR Telescope

Abstract

Relatively little information is available about the Universe at ultra-low radio frequencies, i.e. below 50 MHz (ULF), although the ULF spectral window contains a wealth of unique diagnostics for studying galactic and extragalactic phenomena. Sub-arcsecond resolution imaging at these frequencies is extremely difficult, due to the long baselines (>1000 km) required and large ionospheric perturbations. We have conducted a pilot project to investigate the ULF performance and potential of the International LOFAR Telescope (ILT), a trans-European interferometric array with baselines up to ~2000 km and observing frequencies down to 10 MHz. We have successfully produced images with sub-arcsecond resolution for 6 radio sources at frequencies down to 30 MHz. This is more than an order of magnitude better resolution than pre-ILT observations at similar frequencies. The six targets that we have imaged (3C 196, 3C 225, 3C 273, 3C 295, 3C 298 and 3C 380) are bright radio sources with compact structures. By comparing our data of 3C 196 and 3C 273 with observations at higher frequencies, we investigate their spatially resolved radio spectral properties. Our success shows that at frequencies down to 30 MHz, sub-arcsecond imaging with the ILT is possible. Further analysis is needed to determine the feasibility of observations of fainter sources or sources with less compact emission.

Accepted to a special issue of A&A on sub-arcsecond imaging with LOFAR. 11 pages, 8 figures, 3 tables

References in corpus (12)

• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey I: A low-frequency extragalactic catalogue
• An optimized algorithm for multi-scale wideband deconvolution of radio astronomical images
• The Very Large Array Low-frequency Sky Survey Redux (VLSSr)
• Extragalactic Peaked-Spectrum Radio Sources at Low Frequencies
• Revisiting the radio interferometer measurement equation. II. Calibration and direction-dependent effects
• The LOFAR LBA Sky Survey I. survey description and preliminary data release
• LOFAR imaging of Cygnus A -- Direct detection of a turnover in the hotspot radio spectra
• Galactic Scale Feedback Observed in the 3C 298 Quasar Host Galaxy
• Subarcsecond international LOFAR radio images of the M82 nucleus at 118 MHz and 154 MHz
• Low-frequency monitoring of flare star binary CR Draconis: Long-term electron-cyclotron maser emission
• Compression of interferometric radio-astronomical data

Cited by in corpus (8)

• The LOFAR LBA Sky Survey II. First data release
• Identifying active galactic nuclei via brightness temperature with sub-arcsecond International LOFAR Telescope observations
• Characterization of the decametre sky at subarcminute resolution
• Perturbative and numerical approach to plasma strong lensing
• The Energetics of the Central Engine in the Powerful Quasar, 3C298
• LOFAR 58 MHz Legacy Survey of the 3CRR Catalog
• The LOFAR sub-arcsecond view of the high-redshift radio relic in PSZ2G091.83+26.11
• The resolved jet of 3C 273 at 150 MHz