Detection of spike-like structures near the front of type-II bursts

¹ Department of Physics, University of Athens, 15783 Athens, Greece
e-mail: kbouratz@phys.uoa.gr
² Department of Physics, University of Ioannina, 45110 Ioannina, Greece
³ Department of Electronics, Technological Educational Institute of Sterea Hellas, 35100 Lamia, Greece

Received: 26 December 2018
Accepted: 19 February 2019

Abstract

Aims. We examine high time resolution dynamic spectra for fine structures in type II solar radio bursts

Methods. We used data obtained with the acousto-optic spectrograph receiver of the Artemis-JLS (ARTEMIS-IV) solar radio spectrograph in the 450–270 MHz range at 10 ms cadence and identified more than 600 short, narrowband features. Their characteristics, such as instantaneous relative bandwidth and total duration were measured and compared with those of spikes embedded in type IV emissions.

Results. Type II associated spikes occur mostly in chains inside or close to the slowly drifting type II emission. These spikes coexist with herringbone and pulsating structures. Their average duration is 96 ms and their average relative bandwidth 1.7%. These properties are not different from those of type IV embedded spikes. It is therefore possible that they are signatures of small-scale reconnection along the type II shock front.