arXiv subjects

Dale E. Gary

Publications and source records attributed to Dale E. Gary.

56 records · Page 4Linked to original sources

arXiv2007

The Ribbon-Like Hard X-Ray Emission in a Sigmoidal Solar Active Region

Solar flare emissions at Halpha and EUV/UV wavelengths often appear in the form of two ribbons, which has been regarded as evidence for a typical configuration of solar magnetic reconnection. However, such a ribbon structure has rarely been observed in hard X-rays (HXRs), although it is expected as well. In this letter, we report a ribbon-like HXR source observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) at energies as high as 25-100 keV during the 2005 May 13 flare. For a qualitative understanding of this unusual HXR morphology, we also note that the source active region appeared in a conspicuous sigmoid shape before the eruption and changed to an arcade structure afterward as observed with the Transition Region and Coronal Explorer (TRACE) at 171 A. We suggest that the ribbon-like HXR structure is associated with the sigmoid-to-arcade transformation during this type of reconnection.

astro-ph↗

arXiv2005

Spatial Evidence for Transition Radiation in a Solar Radio Burst

Microturbulence, i.e. enhanced fluctuations of plasma density, electric and magnetic fields, is of great interest in astrophysical plasmas, but occurs on spatial scales far too small to resolve by remote sensing, e.g., at ~ 1-100 cm in the solar corona. This paper reports spatially resolved observations that offer strong support for the presence in solar flares of a suspected radio emission mechanism, resonant transition radiation, which is tightly coupled to the level of microturbulence and provides direct diagnostics of the existence and level of fluctuations on decimeter spatial scales. Although the level of the microturbulence derived from the radio data is not particularly high, <Δn^2 >/n^2 ~ 10^{-5}$, it is large enough to affect the charged particle diffusion and give rise to effective stochastic acceleration. This finding has exceptionally broad astrophysical implications since modern sophisticated numerical models predict generation of much stronger turbulence in relativistic objects, e.g., in gamma-ray burst sources.

astro-ph↗