2006/03/31 by Wei Liu, Siming Liu, Yan Wei Jiang +2 · 1 citation
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Ionosphere and magnetosphere dynamics #Solar and Space Plasma Dynamics #astro-ph
paper · pdf · doi:10.1086/506268
published as Astrophys.J.649:1124-1139,2006 · 36 pages, 14 figures (ApJ Vol. 649, No. 1, Sept 20, 2006, in press)
arxiv created 2006/06/06 · openalex publication_date 2006/09/27 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We present analyses of the spatial and spectral evolution of hard X-ray emission observed by RHESSI during the impulsive phase of an M1.7 flare on 2003 November 13. In general, as expected, the loop top (LT) source dominates at low energies, while the footpoint (FP) sources dominate the high-energy emission. At intermediate energies, both the LT and FPs may be seen, but during certain intervals emission from the legs of the loop dominates, in contrast to the commonly observed LT and FP emission. The hard X-ray emission tends to rise above the FPs and eventually merge into a single LT source. This evolution starts at low energies and proceeds to higher energies. The spectrum of the resultant LT source becomes more and more dominated by a thermal component with an increasing emission measure as the flare proceeds. The soft and hard X-rays show a Neupert-type behavior. With a nonthermal bremsstrahlung model, the brightness profile along the loop is used to determine the density profile and its evolution, which reveals a gradual increase of the gas density in the loop. These results are evidence for chromospheric evaporation and are consistent with the qualitative features of hydrodynamic simulations of this phenomenon. However, some observed source morphologies and their evolution cannot be accounted for by previous simulations. Therefore, simulations with more realistic physical conditions are required to explain the results and the particle acceleration and plasma heating processes.