Ultra-steep spectrum emission in the merging galaxy cluster Abell 1914^⋆

¹ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
e-mail: mandal@strw.leidenuniv.nl
² ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2 7990 AA Dwingeloo, The Netherlands
³ Dipartimento di Fisica e Astronomia, Università di Bologna, via P. Gobetti 93/2, 40129 Bologna, Italy
⁴ INAF – IRA, via P. Gobetti 101, 40129 Bologna, Italy
⁵ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁶ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁷ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
⁸ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
⁹ Naval Research Laboratory, 4555 Overlook Avenue SW, Code 7213, Washington, DC, 20375, USA

Received: 31 July 2018
Accepted: 29 October 2018

Abstract

A number of radio observations have revealed the presence of large synchrotron-emitting sources associated with the intra-cluster medium. There is strong observational evidence that the emitting particles have been (re-)accelerated by shocks and turbulence generated during merger events. The particles that are accelerated are thought to have higher initial energies than those in the thermal pool but the origin of such mildly relativistic particles remains uncertain and needs to be further investigated. The galaxy cluster Abell 1914 is a massive galaxy cluster in which X-ray observations show clear evidence of merging activity. We carried out radio observations of this cluster with the LOw Frequency ARay (LOFAR) at 150 MHz and the Giant Metrewave Radio Telescope (GMRT) at 610 MHz. We also analysed Very Large Array (VLA) 1.4 GHz data, archival GMRT 325 MHz data, CFHT weak lensing data and Chandra observations. Our analysis shows that the ultra-steep spectrum source (4C38.39; α ≲ −2), previously thought to be part of a radio halo, is a distinct source with properties that are consistent with revived fossil plasma sources. Finally, we detect some diffuse emission to the west of the source 4C38.39 that could belong to a radio halo.