First frequency-time-resolved imaging spectroscopy observations of solar radio spikes

Clarkson, D., Kontar, E. P. , Gordovskyy, M., Chrysaphi, N. and Vilmer, N. (2021) First frequency-time-resolved imaging spectroscopy observations of solar radio spikes. Astrophysical Journal Letters, 917(2), L32. (doi: 10.3847/2041-8213/ac1a7d)

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Abstract

Solar radio spikes are short duration and narrow bandwidth fine structures in dynamic spectra observed from the GHz to tens of MHz range. Their very short duration and narrow frequency bandwidth are indicative of subsecond small-scale energy release in the solar corona, yet their origin is not understood. Using the LOw Frequency ARray, we present spatially, frequency, and time resolved observations of individual radio spikes associated with a coronal mass ejection. Individual radio spike imaging demonstrates that the observed area is increasing in time and the centroid positions of the individual spikes move superluminally parallel to the solar limb. Comparison of spike characteristics with that of individual Type IIIb striae observed in the same event show similarities in duration, bandwidth, drift rate, polarization, and observed area, as well the spike and striae motion in the image plane suggesting fundamental plasma emission with the spike emission region on the order of ∼108 cm, with brightness temperature as high as 1013 K. The observed spatial, spectral, and temporal properties of the individual spike bursts are also suggestive of the radiation responsible for spikes escaping through anisotropic density turbulence in closed loop structures with scattering preferentially along the guiding magnetic field oriented parallel to the limb in the scattering region. The dominance of scattering on the observed time profile suggests the energy release time is likely to be shorter than what is often assumed. The observations also imply that the density turbulence anisotropy along closed magnetic field lines is higher than along open field lines.

Item Type:Articles
Additional Information:D.L.C., E.P.K., and N.V. are thankful to Dstl for the funding through the UK-France PhD Scheme (contract DSTLX-1000106007). E.P.K. was supported by STFC consolidated grant ST/P000533/1. M.G. was supported by the STFC grant ST/T00035X/1. N.C. thanks CNES for its financial support. 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 obtained 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. The authors thank the radio astronomy station of Nançay/Scientific Unit of Nançay of the Paris Observatory (USR 704-CNRS, supported by the University of Orleans, the OSUC and the Center Region in France) for providing access to NDA observations accessible online at https://www.obsnancay.fr.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Chrysaphi, Dr Nicolina and Kontar, Professor Eduard and Vilmer, Dr Nicole and Clarkson, Daniel
Authors: Clarkson, D., Kontar, E. P., Gordovskyy, M., Chrysaphi, N., and Vilmer, N.
College/School:College of Science and Engineering
College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal Letters
Publisher:IOP Publishing
ISSN:2041-8205
ISSN (Online):2041-8213
Copyright Holders:Copyright © 2021 The Authors
First Published:First published in Astrophysical Journal Letters 917(2):L32
Publisher Policy:Reproduced under a Creative Commons License
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
173390UK-France Joint PhD programme 2016: Imaging and spectroscopic imaging of solar radio sources with LOFAREduard KontarDefence Science and Technology Laboratory (DSTL)DSTLX1000106007_GLASP&S - Physics & Astronomy
173869Consolidated Grant in Solar PhysicsLyndsay FletcherScience and Technology Facilities Council (STFC)ST/P000533/1P&S - Physics & Astronomy