Hinode X-Ray Telescope Detection of Hot Emission from Quiescent Active Regions: A Nanoflare Signature?
Klimchuk, J. A.; Golub, L.; Schmelz, J. T.; DeLuca, E. E.; Saar, S. H.; Kashyap, V. L.; Weber, M. A.
United States
Abstract
The X-Ray Telescope (XRT) on the Japanese/USA/UK Hinode (Solar-B) spacecraft has detected emission from a quiescent active region core that is consistent with nanoflare heating. The fluxes from 10 broadband X-ray filters and filter combinations were used to construct differential emission measure (DEM) curves. In addition to the expected active region peak at log T = 6.3-6.5, we find a high-temperature component with significant emission measure at log T > 7.0. This emission measure is weak compared to the main peak—the DEM is down by almost three orders of magnitude—which accounts of the fact that it has not been observed with earlier instruments. It is also consistent with spectra of quiescent active regions: no Fe XIX lines are observed in a CHIANTI synthetic spectrum generated using the XRT DEM distribution. The DEM result is successfully reproduced with a simple two-component nanoflare model.