2018/10/01 by Anton Reva, A. A. Reva, A. S. Ulyanov +6 · 15 citations
Physics and Astronomy · #Astro and Planetary Science #Astrophysics #Ionosphere and magnetosphere dynamics #Limit (mathematics) #Measure (data warehouse) #Nuclear physics #Physics #Plasma #Solar and Space Plasma Dynamics #astro-ph.SR
paper · pdf · doi:10.1007/s11207-018-1363-9
published in Solar Physics 293(10) (Springer Science+Business Media)
openalex publication_date 2018/10/01 · arxiv created 2018/10/11 · arxiv updated 2018/10/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The nanoflare-heating theory predicts steady hot plasma emission in the non-flaring active regions. It is hard to find this emission with conventional non-monochromatic imagers (such as Atmospheric Imaging Assembly or X-Ray Telescope), because their images contain a cool temperature background. In this work, we search for hot plasma in non-flaring active regions using the Mg XII spectroheliograph onboard Complex Orbital Observations Near-Earth of Activity on the Sun (CORONAS)-F/SPectroheliographIc X-ray Imaging Telescope (SPIRIT). This instrument acquired monochromatic images of the solar corona in the Mg XII 8.42 Åline, which emits only at temperatures higher than 4 MK. The Mg XII images contain the signal only from hot plasma without any low-temperature background. We studied the hot plasma in active regions using the SPIRIT data from 18-28 February 2002. During this period, the Mg XII spectroheliograph worked with a 105-second cadence almost without data gaps. The hot plasma was observed only in the flaring active regions. We do not observe any hot plasma in non-flaring active regions. The hot plasma column emission measure in the non-flaring active region should not exceed 3 × 1024 cm-5. The hot Differential Emission Measure (DEM) is less than 0.01 % of the DEM of the main temperature component. Absence of Mg XII emission in the non-flaring active regions can be explained by weak and frequent nanoflares (delay less than 500 seconds) or by very short and intense nanoflares that lead to non-equilibrium ionization.