Spectral and imaging observations of a white-light solar flare in the mid-infrared

Penn M.; Krucker S.; Hudson H.; Jhabvala M.; Jennings D.; Lunsford A.; Kaufmann P.

Spectral and imaging observations of a white-light solar flare in the mid-infrared

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Artigo

Date

2016

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Astrophysical Journal Letters

item.page.citationsscopus

26

Authors

Penn M.
Krucker S.
Hudson H.
Jhabvala M.
Jennings D.
Lunsford A.
Kaufmann P.

Abstract

© 2016. The American Astronomical Society. All rights reserved.We report high-resolution observations at mid-infrared wavelengths of a minor solar flare, SOL2014-09-24T17:50 (C7.0), using Quantum Well Infrared Photodetector cameras at an auxiliary of the McMath-Pierce telescope. The flare emissions, the first simultaneous observations in two mid-infrared bands at 5.2 and 8.2 μm with white-light and hard X-ray coverage, revealed impulsive time variability with increases on timescales of ∼4 s followed by exponential decay at ∼10 s in two bright regions separated by about 13.,c. The brightest source is compact, unresolved spatially at the diffraction limit (1. 72 .,c at 5.2 μm ). We identify the IR sources as flare ribbons also seen in white-light emission at 6173 A.,Qobserved by SDO/HMI, with twin hard X-ray sources observed by Reuven Ramaty High Energy Solar Spectroscopic Imager, and with EUV sources (e.g., 94 A) observed by SDO/AIA. The two infrared points have nearly the same flux density (fh, Wm-2 Hz) and extrapolate to a level of about an order of magnitude below that observed in the visible band by HMI, but with a flux of more than two orders of magnitude above the free-free continuum from the hot (∼15 MK) coronal flare loop observed in the X-ray range. The observations suggest that the IR emission is optically thin; this constraint and others suggest major contributions from a density less than about 4 ×1013 cm-3. We tentatively interpret this emission mechanism as predominantly free-free emission in a highly ionized but cool and rather dense chromospheric region.