Hot plasma in a quiescent solar active region as measured by RHESSI, XRT, and AIA. (arXiv:1903.11293v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ishikawa_S/0/1/0/all/0/1">Shin-nosuke Ishikawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Krucker_S/0/1/0/all/0/1">Sam Krucker</a>
This paper investigates a quiescent (non-flaring) active region observed on
July 13, 2010 in EUV, SXR, and HXRs to search for a hot component that is
speculated to be a key signature of coronal heating. We use a combination of
RHESSI imaging and long-duration time integration (up to 40 min) to detect the
active regions in the 3-8 keV range during apparently non-flaring times. The
RHESSI imaging reveals a hot component that originates from the entire active
region, as speculated for a nanoflare scenario where the entire active region
is filled with a large number of unresolved small energy releases. An
isothermal fit to the RHESSI data gives temperatures around ~7 MK with emission
measure of several times 10^46 cm^-3. Adding EUV and SXR observations taken by
AIA and XRT, respectively, we derive a differential emission measure (DEM) that
shows a peak between 2 and 3 MK with a steeply decreasing high-temperature
tail, similar to what has been previously reported. The derived DEM reveals
that a wide range of temperatures contributes to the RHESSI flux (e.g. 40 % of
the 4 keV emission being produced by plasma below 5 MK, while emission at 7 keV
is almost exclusively from plasmas above 5 MK) indicating that the RHESSI
spectrum should not be fitted with an isothermal. The hot component has a
rather small emission measure (~0.1 % of the total EM is above 5 MK), and the
derived thermal energy content is of the order of 10 % for a filling factor of
unity, or potentially below 1 % for smaller filling factors.
This paper investigates a quiescent (non-flaring) active region observed on
July 13, 2010 in EUV, SXR, and HXRs to search for a hot component that is
speculated to be a key signature of coronal heating. We use a combination of
RHESSI imaging and long-duration time integration (up to 40 min) to detect the
active regions in the 3-8 keV range during apparently non-flaring times. The
RHESSI imaging reveals a hot component that originates from the entire active
region, as speculated for a nanoflare scenario where the entire active region
is filled with a large number of unresolved small energy releases. An
isothermal fit to the RHESSI data gives temperatures around ~7 MK with emission
measure of several times 10^46 cm^-3. Adding EUV and SXR observations taken by
AIA and XRT, respectively, we derive a differential emission measure (DEM) that
shows a peak between 2 and 3 MK with a steeply decreasing high-temperature
tail, similar to what has been previously reported. The derived DEM reveals
that a wide range of temperatures contributes to the RHESSI flux (e.g. 40 % of
the 4 keV emission being produced by plasma below 5 MK, while emission at 7 keV
is almost exclusively from plasmas above 5 MK) indicating that the RHESSI
spectrum should not be fitted with an isothermal. The hot component has a
rather small emission measure (~0.1 % of the total EM is above 5 MK), and the
derived thermal energy content is of the order of 10 % for a filling factor of
unity, or potentially below 1 % for smaller filling factors.
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