A multiwavelength study of solar Ellerman bombs.

摘要

Solar Ellerman bombs (also known as moustaches) are small {dollar}(approx{dollar}1 arcsec) bright structures which appear in solar active regions. It was the purpose of this study to determine their fundamental character. Are Ellerman bombs a flare-like phenomenon or do they represent an in-situ, driven release of energy? In order to answer this question and others, several different aspects of bomb behavior were analyzed. Photometric analysis of their optical emission indicates that bombs are constrained to a 500 km region in the lower chromosphere ranging from {dollar}approx{dollar}500-1000 km above the {dollar}tausb{lcub}5000{rcub}{dollar} = 1 level. They have lifetimes of 15 minutes and exhibit time profiles of rapid rise and rapid decay that are not convincingly similar to flares which generally show rapid rise and slow decay. Simultaneous optical, microwave, and soft x-ray observations detected no coronal or upper chromospheric emission associated with Ellerman bombs, thereby constraining the bomb emission to the lower chromosphere and virtually eliminating the possibility of a triggering mechanism high in the atmosphere. The radio (2 and 3.6 cm) and soft x-ray observations, however, did detect faint microwave "twinklings" which appeared to be cospatial with the footpoint of a coronal soft x-ray loop but which were not associated with an Ellerman bomb. High spatial resolution {dollar}rm Halpha - 1A{dollar} movies show some bombs moving radially out from the outer edge of the penumbra into the surrounding undisturbed granulation pattern. High spatial resolution {dollar}rm Halpha - 1A{dollar} images deconvolved using a Quasi-Weiner filter, revealed that elliptical bombs appear to consist of two or more emission structures on scales {dollar}le{dollar}.5 arcsec. The optical energy output of a typical Ellerman bomb with a lifetime of 840 seconds and an area of 10{dollar}sp{lcub}16{rcub}cmsp{lcub}-2{rcub}{dollar} was estimated to be a minimum of 3.2 {dollar}times{dollar} 10{dollar}sp{lcub}27{rcub}ergs.{dollar} This is shown to be on the order of the energy in a photospheric magnetic field of 1000 G contained in a volume of 1000 km x 1000 km x 500 km (the volume of a typical Ellerman bomb). This was also shown to be on the order of the upper limit of the energy output of non-thermal gyro-synchrotron-producing elections located at a height of 2000 km where the {dollar}tausb{lcub}2cm{rcub}{dollar} = 1. However, a mechanism which could transport these electrons {dollar}(E>100{dollar} keV) into the deep chromosphere without depositing electrons with lower energies into the upper chromosphere was not forthcoming. The plasma {dollar}beta{dollar} in the Ellerman bomb was found to range from 0.017 to 0.17 depending on the estimate of the magnetic field strength. The observations suggest that energy released in-situ near the {dollar}betaapprox 1{dollar} regime is responsible for the Ellerman bomb phenomenon. This poses difficulties, however, for both driven mechanisms and storage/unloading mechanisms.