THE SUB-ARCSECOND HARD X-RAY STRUCTURE OF LOOP FOOTPOINTS IN A SOLAR FLARE

Journal Article · Thu Jul 01 04:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/717/1/250· OSTI ID:21452876

Kontar, E P; Hannah, I G; Jeffrey, N L. S.; Battaglia, M ^[1]

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1. Department of Physics and Astronomy, University of Glasgow, G12 8QQ (United Kingdom)

The newly developed X-ray visibility forward fitting technique is applied to the RHESSI data of a limb flare to investigate the energy and height dependence on sizes, shapes, and position of hard X-ray (HXR) chromospheric footpoint sources. This provides information about the electron transport and chromospheric density structure. The spatial distribution of two footpoint X-ray sources is analyzed using PIXON, Maximum Entropy Method, CLEAN, and visibility forward fit algorithms at nonthermal energies from {approx}20 to {approx}200 keV. We report, for the first time, the vertical extents and widths of HXR chromospheric sources measured as a function of energy for a limb event. Our observations suggest that both the vertical and horizontal sizes of footpoints are decreasing with energy. Higher energy emission originates progressively deeper in the chromosphere, consistent with downward flare accelerated streaming electrons. The ellipticity of the footpoints grows with energy from {approx}0.5 at {approx}20 keV to {approx}0.9 at {approx}150 keV. The positions of X-ray emission are in agreement with an exponential density profile of scale height {approx}150 km. The characteristic size of the HXR footpoint source along the limb decreases with energy, suggesting a converging magnetic field in the footpoint. The vertical sizes of X-ray sources are inconsistent with simple collisional transport in a single density scale height but can be explained using a multi-threaded density structure in the chromosphere.

• OSTI ID: 21452876
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 717; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ATMOSPHERES
CHROMOSPHERE
DIMENSIONS
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
ENERGY DEPENDENCE
ENTROPY
FERMIONS
HARD X RADIATION
HEIGHT
IONIZING RADIATIONS
LEPTONS
MAGNETIC FIELDS
MAIN SEQUENCE STARS
PHYSICAL PROPERTIES
RADIATION SOURCES
RADIATIONS
SCALE HEIGHT
SOLAR ACTIVITY
SOLAR ATMOSPHERE
SOLAR FLARES
STARS
STELLAR ACTIVITY
STELLAR ATMOSPHERES
STELLAR FLARES
SUN
THERMODYNAMIC PROPERTIES
X RADIATION
X-RAY SOURCES