Solar radio spikes and type IIIb striae manifestations of subsecond electron acceleration triggered by a coronal mass ejection

Clarkson, D. L. , Kontar, E. P. , Vilmer, N., Gordovskyy, M., Chen, X. and Chrysaphi, N. (2023) Solar radio spikes and type IIIb striae manifestations of subsecond electron acceleration triggered by a coronal mass ejection. Astrophysical Journal, 946(1), 33. (doi: 10.3847/1538-4357/acbd3f)

Abstract

Understanding electron acceleration associated with magnetic energy release at subsecond scales presents major challenges in solar physics. Solar radio spikes observed as subsecond, narrow-bandwidth bursts with Δf/f ∼ 10−3–10−2 are indicative of a subsecond evolution of the electron distribution. We present a statistical analysis of frequency- and time-resolved imaging of individual spikes and Type IIIb striae associated with a coronal mass ejection (CME). LOFAR imaging reveals that the cotemporal (<2 s) spike and striae intensity contours almost completely overlap. On average, both burst types have a similar source size with a fast expansion at millisecond scales. The radio source centroid velocities are often superluminal and independent of frequency over 30–45 MHz. The CME perturbs the field geometry, leading to increased spike emission likely due to frequent magnetic reconnection. As the field restores itself toward the prior configuration, the observed sky-plane emission locations drift to increased heights over tens of minutes. Combined with previous observations above 1 GHz, the average decay time and source size estimates follow a ∼1/f dependence over three decades in frequency, similar to radio-wave scattering predictions. Both time and spatial characteristics of the bursts between 30 and 70 MHz are consistent with radio-wave scattering with a strong anisotropy of the density fluctuation spectrum. Consequently, the site of the radio-wave emission does not correspond to the observed burst locations and implies acceleration and emission near the CME flank. The bandwidths suggest intrinsic emission source sizes <1'' at 30 MHz and magnetic field strengths a factor of two larger than average in events that produce decameter spikes.

• Item Type: Articles
• Additional Information: DLC, EPK, and NV are thankful to Dstl for the funding through the UK-France PhD Scheme (contract DSTLX-1000106007). EPK, XC are supported by STFC consolidated grant ST/T000422/1. NC thanks CNES for its financial support. We gratefully acknowledge the UK-France collaboration grant provided by the British Council Hubert Curien Alliance Programme that con- tributed to the completion of this work. The authors acknowledge the support by the international team grant (http://www.issibern.ch/teams/lofar/) from ISSI Bern, Switzerland. This paper is based (in part) on data ob- tained from facilities of the International LOFAR Telescope (ILT) under project code LC8_027. LOFAR (van Haarlem et al. 2013) is the Low-Frequency Array designed and constructed by ASTRON. It has observing, data processing, and data storage facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the ILT Foundation under a joint scientific policy. The ILT resources have benefited from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Université d’Orléans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Kontar, Professor Eduard and Clarkson, Dr Daniel and Vilmer, Dr Nicole and Chrysaphi, Dr Nicolina and Chen, Dr Xingyao
• Authors: Clarkson, D. L., Kontar, E. P., Vilmer, N., Gordovskyy, M., Chen, X., and Chrysaphi, N.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Astrophysical Journal
• Publisher: IOP Publishing
• ISSN: 0004-637X
• ISSN (Online): 1538-4357
• Published Online: 24 March 2023
• Copyright Holders: Copyright © 2023 The Authors
• First Published: First published in Astrophysical Journal 946(1): 33
• Publisher Policy: Reproduced under a Creative Commons License

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
306515		PHAS A&A Group STFC Consolidated	Lyndsay Fletcher	Science and Technology Facilities Council (STFC)	ST/T000422/1	P&S - Physics & Astronomy