What Is the Spatial Relationship between Hard X‐Ray Footpoints and Vertical Electric Currents in Solar Flares?

Abstract

We examine the spatial relationship between solar hard X-ray sources observed with the Hard X-Ray Telescope aboard Yohkoh and photospheric electric currents observed at Mees Solar Observatory. In 1993, Canfield et al. concluded that energetic electron precipitation tends to occur at the edge of sites of high vertical current. They did not, however, have a direct diagnostic of particle precipitation; they used Hα Stark-wing emission as a proxy. In this paper, we analyze hard X-ray images and vector magnetograms of six flares of M/X X-ray class to reach two basic conclusions. First, we confirm that electron precipitation avoids sites of high vertical current density at photospheric levels, preferentially occurring adjacent to these current channels. Hence, we conclude that our observations rule out flare models in which nonthermal electrons are accelerated within the large-scale active-region current systems that are observed by present vector magnetographs. Second, at conjugate magnetic footpoints the stronger hard X-ray emission is associated with smaller vertical current density and weaker magnetic field. This result is consistent with a "cornucopia"-shaped magnetic morphology in which precipitating electrons are preferentially deflected away from the narrower footpoint by magnetic mirroring.