From large-scale loops to the sites of dense flaring loops: preferential conditions for long-period pulsations in solar flares

Foullon, C., Fletcher, L. , Hannah, I.G. , Verwichte, E., Cecconi, B., Nakariakov, V.M., Phillips, K.J.H. and Tan, B.L. (2010) From large-scale loops to the sites of dense flaring loops: preferential conditions for long-period pulsations in solar flares. Astrophysical Journal, 719(1), pp. 151-165. (doi:10.1088/0004-637X/719/1/151)

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Abstract

Long-period quasi-periodic pulsations (QPPs) of solar flares are a class apart from shorter period events. By involving an external resonator, the mechanism they call upon differs from traditional QPP models, but has wider applications. We present a multi-wavelength analysis of spatially resolved QPPs, with periods around 10 minutes, observed in the X-ray spectrum primarily at energies between 3 and 25 keV. Complementary observations obtained in Hα and radio emission in the kHz to GHz frequency range, together with an analysis of the X-ray plasma properties provide a comprehensive picture that is consistent with a dense flaring loop subject to periodic energization and thermalization. The QPPs obtained in Hα and type III radio bursts, with similar periods as the QPPs in soft X-rays, have the longest periods ever reported for those types of data sets. We also report 1-2 GHz radio emission, concurrent with but unrestricted to the QPP time intervals, which is multi-structured at regularly separated narrowband frequencies and modulated with ~18 minute periods. This radio emission can be attributed to the presence of multiple "quiet" large-scale loops in the background corona. Large scale but shorter inner loops below may act as preferential resonators for the QPPs. The observations support interpretations consistent with both inner and outer loops subject to fast kink magnetohydrodynamic waves. Finally, X-ray imaging indicates the presence of double coronal sources in the flaring sites, which could be the particular signatures of the magnetically linked inner loops. We discuss the preferential conditions and the driving mechanisms causing the repeated flaring.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Fletcher, Professor Lyndsay and Hannah, Dr Iain
Authors: Foullon, C., Fletcher, L., Hannah, I.G., Verwichte, E., Cecconi, B., Nakariakov, V.M., Phillips, K.J.H., and Tan, B.L.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
ISSN:0004-637X
ISSN (Online):1538-4357
Published Online:19 July 2010

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
465931Solar, stellar and cosmological plasmas: a synthesis of data, modelling and theory.Declan DiverScience & Technologies Facilities Council (STFC)ST/F002149/1Physics and Astronomy