THE HEIGHT OF A WHITE-LIGHT FLARE AND ITS HARD X-RAY SOURCES

• Published in: Astrophysical journal. Letters Vol. 753; no. 2; pp. 1 - 5
• Main Authors: Oliveros, Juan-Carlos Martinez, Hudson, Hugh S, Hurford, Gordon J, Krucker, Sam, Lin, R P, Lindsey, Charles, COUVIDAT, SEBASTIEN, Schou, Jesper, Thompson, W T
• Format: Journal Article
• Language: English
• Published: United States 10.07.2012
• Subjects: ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Centroids; Continuums; DISTANCE; ELECTRONS; Estimates; Flares; HARD X RADIATION; KEV RANGE; PHOTONS; PHOTOSPHERE; SOLAR FLARES; SUN; VISIBLE RADIATION; White light
• ISSN: 2041-8205; 2041-8213
• DOI: 10.1088/2041-8205/753/2/L26

We describe observations of a white-light (WL) flare (SOL2011-02-24T07:35:00, M3.5) close to the limb of the Sun, from which we obtain estimates of the heights of the optical continuum sources and those of the associated hard X-ray (HXR) sources. For this purpose, we use HXR images from the Reuven Ramaty High Energy Spectroscopic Imager and optical images at 6173 [Angstrom] from the Solar Dynamics Observatory. We find that the centroids of the impulsive-phase emissions in WL and HXRs (30-80 keV) match closely in central distance (angular displacement from Sun center), within uncertainties of order 0".2. This directly implies a common source height for these radiations, strengthening the connection between visible flare continuum formation and the accelerated electrons. We also estimate the absolute heights of these emissions as vertical distances from Sun center. Such a direct estimation has not been done previously, to our knowledge. Using a simultaneous 195 [Angstrom] image from the Solar-Terrestrial RElations Observatory spacecraft to identify the heliographic coordinates of the flare footpoints, we determine mean heights above the photosphere (as normally defined; [tau] = 1 at 5000 [Angstrom]) of 305 + or - 170 km and 195 + or - 70 km, respectively, for the centroids of the HXR and WL footpoint sources of the flare. These heights are unexpectedly low in the atmosphere, and are consistent with the expected locations of [tau] = 1 for the 6173 [Angstrom] and the ~40 keV photons observed, respectively.