Energetics and Occurrence Rate of Active-Region Transient Brightenings and Implications for the Heating of the Active-Region Corona

Details Energetics and Occurrence Rate of Active-Region Transient Brightenings and Implications for the Heating of the Active-Region Corona Energetics and Occurrence Rate of Active-Region Transient Brightenings and Implications for the Heating of the Active-Region Corona

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995pasj...47..251s&link_type=abstract

Publications of the Astronomical Society of Japan, v.47, p.251-263.

Astronomy and Astrophysics

Astronomy

204

Active Regions, Coronal Heating, Sun: Activity Sun: Corona, Sun: X-Rays

Scientific paper

Frequent transient brightenings have been discovered in solar active regions using the Yohkoh Soft X-ray Telescope. We examine the possibility that these transient brightenings have much contribution to heating of the active-region corona. Imaging observations provide the following physical conditions: temperature, 4--8 MK; emission measure, 10(44.5) --10(47.5) cm(-3) ; electron density, 2 times 10(9) --2 times 10(10) cm(-3) ; gas pressure, 5--20 dyne cm(-2) ; loop length, 5 times 10(3) --4 times 10(4) km; loop width, 2 times 10(3) --7 times 10(3) km; and duration, 2--7 min. The energy involved in the observed transient brightenings is estimated to range from 10(25) to 10(29) erg. The frequency distribution as a function of the energy can be represented by a single power-law with an index of 1.5--1.6 in the energy range greater than 10(27) erg, although the distribution deviates from a power-law in the energy range less than 10(27) erg due to the instrument dead time and/or obscuration by bright coronal features. The single power-law of the frequency distribution thus appears to extend from the solar flare range down to an energy of 10(27) erg. The total energy supplied by transient brightenings and flares, assuming that the power-law continues to lower energy, is estimated to be at most a factor of 5 smaller than the heating rate required for the active-region corona. We need weaker events with an occurrence rate much higher than the extrapolated power-law to explain the heating of the active-region corona with transient brightenings.

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