First look at the giant radio galaxy 3C 236 with LOFAR^⋆

¹ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
e-mail: a.shulevski@uva.nl
² ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
³ University of Groningen, Kapteyn Astronomical Institute, Landleven 12, 9747 AD Groningen, The Netherlands
⁴ Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
⁵ INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
⁶ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁷ School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁸ Space Science & Technology Department, The Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0NL, UK
⁹ School of Physics, University College Dublin, Belfield, Dublin 4, UK
¹⁰ Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

Received: 30 March 2019
Accepted: 19 July 2019

Abstract

We have examined the giant radio galaxy 3C 236 using LOFAR at 143 MHz down to an angular resolution of 7″, in combination with observations at higher frequencies. We used the low frequency data to derive spectral index maps with the highest resolution yet at these low frequencies. We confirm a previous detection of an inner hotspot in the north-west lobe and for the first time observe that the south-east lobe hotspot is in fact a triple hotspot, which may point to an intermittent source activity. Also, the spectral index map of 3C 236 shows that the spectral steepening at the inner region of the northern lobe is prominent at low frequencies. The outer regions of both lobes show spectral flattening, in contrast with previous high frequency studies. We derive spectral age estimates for the lobes, as well as particle densities of the IGM at various locations. We propose that the morphological differences between the lobes are driven by variations in the ambient medium density as well as the source activity history.