Spectral analysis of spatially resolved 3C295 (sub-arcsecond resolution) with the International LOFAR Telescope^★

¹ Universita di Bologna, Via Zamboni, 33, 40126 Bologna BO, Italy
e-mail: etienne.bonnassieux@unibo.it
² INAF, Instituto di Radioastronomia, Via Piero Gobetti, 101, 40129 Bologna BO, Italy
³ Leiden Observatory, Leiden University, PO Box 9513, 2300RA Leiden, The Netherlands
⁴ Thüringer Landessternwarte (TLS), Sternwarte 5, 07778 Tautenburg, Germany
⁵ CSIRO Astronomy and Space Science, PO Box 1130, Bentley, WA 6102, Australia
⁶ University of Manchester, Department of Physics and Astronomy, School of Natural Sciences, University of Manchester, Manchester M13 9PL, UK
⁷ Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham DH1 3LE, UK
⁸ Institute for Computational Cosmology, Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK
⁹ Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK
¹⁰ GEPI, Observatoire de Paris, 5 place Jules Janssen, 92190 Meudon, France
¹¹ Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Emil-Fischer-Str. 31, 97074 Würzburg, Germany

Received: 6 July 2021
Accepted: 4 September 2021

Abstract

3C295 is a bright, compact steep spectrum source with a well-studied integrated radio spectral energy distribution (SED) from 132 MHz to 15 GHz. However, spatially resolved spectral studies have been limited due to a lack of high resolution images at low radio frequencies. These frequencies are crucial for measuring absorption processes, and anchoring the overall spectral modelling of the radio SED. In this paper, we use International LOw-Frequency ARray (LOFAR) Telescope (ILT) observations of 3C295 to study its spatially resolved spectral properties with sub-arcsecond resolution at 132 MHz. Combining our new 132 MHz observation with archival data at 1.6, 4.8, and 15 GHz, we are able to carry out a resolved radio spectral analysis. The spectral properties of the hotspots provides evidence for low frequency flattening. In contrast, the spectral shape across the lobes is consistent with a Jaffe-Perola spectral ageing model. Using the integrated spectral information for each component, we then fitted low-frequency absorption models to the hotspots, finding that both free-free absorption and synchrotron self-absorption models provide a better fit to the data than a standard power law. Although we can say there is low-frequency absorption present in the hotspots of 3C295, future observations with the Low Band Antenna of the ILT at 55 MHz may allow us to distinguish the type of absorption.