MEASUREMENTS OF THE CORONAL ACCELERATION REGION OF A SOLAR FLARE

Journal Article · Mon May 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/714/2/1108· OSTI ID:21448844

Krucker, Saem; Hudson, H S; Glesener, L; Lin, R P ^[1]; White, S M ^[2]; Masuda, S ^[3]

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1. Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States)
2. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
3. Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan)

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Nobeyama Radioheliograph (NoRH) are used to investigate coronal hard X-ray and microwave emissions in the partially disk-occulted solar flare of 2007 December 31. The STEREO mission provides EUV images of the flare site at different viewing angles, establishing a two-ribbon flare geometry and occultation heights of the RHESSI and NoRH observations of {approx}16 Mm and {approx}25 Mm, respectively. Despite the occultation, intense hard X-ray emission up to {approx}80 keV occurs during the impulsive phase from a coronal source that is also seen in microwaves. The hard X-ray and microwave source during the impulsive phase is located {approx}6 Mm above thermal flare loops seen later at the soft X-ray peak time, similar in location to the above-the-loop-top source in the Masuda flare. A single non-thermal electron population with a power-law distribution (with spectral index of {approx}3.7 from {approx}16 keV up to the MeV range) radiating in both bremsstrahlung and gyrosynchrotron emission can explain the observed hard X-ray and microwave spectrum, respectively. This clearly establishes the non-thermal nature of the above-the-loop-top source. The large hard X-ray intensity requires a very large number (>5 x 10{sup 35} above 16 keV for the derived upper limit of the ambient density of {approx}8 x 10{sup 9} cm{sup -3}) of suprathermal electrons to be present in this above-the-loop-top source. This is of the same order of magnitude as the number of ambient thermal electrons. We show that collisional losses of these accelerated electrons would heat all ambient electrons to superhot temperatures (tens of keV) within seconds. Hence, the standard scenario, with hard X-rays produced by a beam comprising the tail of a dominant thermal core plasma, does not work. Instead, all electrons in the above-the-loop-top source seem to be accelerated, suggesting that the above-the-loop-top source is itself the electron acceleration region.

• OSTI ID: 21448844
• Journal Information: Astrophysical Journal, Vol. 714, Issue 2; Other Information: DOI: 10.1088/0004-637X/714/2/1108; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
BREMSSTRAHLUNG
ECLIPSE
ELECTRONS
EMISSION
GAMMA RADIATION
HARD X RADIATION
MICROWAVE RADIATION
MICROWAVE SPECTRA
SOFT X RADIATION
SOLAR FLARES
SUN
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
FERMIONS
IONIZING RADIATIONS
LEPTONS
MAIN SEQUENCE STARS
RADIATIONS
SOLAR ACTIVITY
SPECTRA
STARS
STELLAR ACTIVITY
STELLAR FLARES
X RADIATION