Optical spectral observations of a flickering white-light kernel in a C1 solar flare

Kowalski, A. F., Cauzzi, G. and Fletcher, L. (2015) Optical spectral observations of a flickering white-light kernel in a C1 solar flare. Astrophysical Journal, 798(2), 107. (doi:10.1088/0004-637X/798/2/107)

Kowalski, A. F., Cauzzi, G. and Fletcher, L. (2015) Optical spectral observations of a flickering white-light kernel in a C1 solar flare. Astrophysical Journal, 798(2), 107. (doi:10.1088/0004-637X/798/2/107)

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Abstract

We analyze optical spectra of a two-ribbon, long-duration C1.1 flare that occurred on 2011 August 18 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 Å to 4550 Å acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, ≤0.''5 (1015 cm2) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a "blue continuum bump" in the excess emission which may be indicative of the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Fletcher, Professor Lyndsay
Authors: Kowalski, A. F., Cauzzi, G., and Fletcher, L.
College/School:College of Science and Engineering > School of Physics and Astronomy
Research Group:Astronomy & Astrophysics
Journal Name:Astrophysical Journal
Publisher:Institute of Physics Publishing, Inc.
ISSN:‎0004-637X
ISSN (Online):1538-4357
Copyright Holders:Copyright © 2015 American Astronomical Society
First Published:First published in Astrophysical Journal 798(2):107
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
631581Consolidated grant in solar and astrophysical plasmasLyndsay FletcherScience & Technologies Facilities Council (STFC)ST/L000741/1S&E P&A - PHYSICS & ASTRONOMY
595181Chromospheric Flares: Observations, Models and Archives (CHROMA)Lyndsay FletcherEuropean Commission (EC)606862P&A - PHYSICS & ASTRONOMY