Soft X-ray pulsations in solar flares

Simoes, P. J.A. , Hudson, H. S. and Fletcher, L. (2015) Soft X-ray pulsations in solar flares. Solar Physics, 290(12), pp. 3625-3639. (doi:10.1007/s11207-015-0691-2)

Simoes, P. J.A. , Hudson, H. S. and Fletcher, L. (2015) Soft X-ray pulsations in solar flares. Solar Physics, 290(12), pp. 3625-3639. (doi:10.1007/s11207-015-0691-2)

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Abstract

The soft X-ray emissions of solar flares come mainly from the bright coronal loops at the highest temperatures normally achieved in the flare process. Their ubiquity has led to their use as a standard measure of flare occurrence and energy, although the overwhelming bulk of the total flare energy goes elsewhere. Recently Dolla et al. (2012) noted quasi-periodic pulsations (QPP) in the soft X-ray signature of the X-class flare SOL2011-02-15, as observed by the standard photometric data from the GOES (Geostationary Operational Environmental Satellite) spacecraft. In this paper we analyze the suitability of the GOES data for this kind of analysis and find them to be generally valuable after September, 2010 (GOES-15). We then extend the Dolla et al. result to a complete list of X-class flares from Cycle 24, and show that most of them (80%) display QPPs in the impulsive phase. The pulsations show up cleanly in both channels of the GOES data, making use of time-series of irradiance differences (the digital time derivative on the 2-s sampling). We deploy different techniques to characterize the periodicity of GOES pulsations, considering the red-noise properties of the flare signals, finding a range of chracteristic time scales of the QPPs for each event, but usually with no strong signature of a single period dominating in the power spectrum. The QPP may also appear on somewhat longer time scales during the later gradual phase, possibly with a greater tendency towards coherence, but the sampling noise in GOES difference data for large irradiance values (X-class flares) makes these more uncertain. We show that there is minimal phase difference between the differenced GOES energy channels, or between them and the hard X-ray variations on short time scales. During the impulsive phase the footpoints of the newly-forming flare loops may also contribute to the observed soft X-ray variations.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Hudson, Dr Hugh and Simoes, Dr Paulo and Fletcher, Professor Lyndsay
Authors: Simoes, P. J.A., Hudson, H. S., and Fletcher, L.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Solar Physics
Publisher:Springer Netherlands
ISSN:0038-0938
ISSN (Online):1573-093X
Copyright Holders:Copyright © 2015 Springer Netherlands
First Published:First published in Solar Physics 290(12):3625-3639
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher.
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
595181Chromospheric Flares: Observations, Models and Archives (CHROMA)Lyndsay FletcherEuropean Commission (EC)606862P&A - PHYSICS & ASTRONOMY
542081Rolling Programme in Solar and Plasma AstrophysicsLyndsay FletcherScience & Technologies Facilities Council (STFC)ST/I001808/1P&A - PHYSICS & ASTRONOMY