Article

# Evidence of Impulsive Heating in Active Region Core Loops

09/2010; DOI:abs/1009.0663
Source: arXiv

ABSTRACT Using a full spectral scan of an active region from the Extreme-Ultraviolet Imaging Spectrometer (EIS) we have obtained Emission Measure EM$(T)$ distributions in two different moss regions within the same active region. We have compared these with theoretical transition region EMs derived for three limiting cases, namely \textit{static equilibrium}, \textit{strong condensation} and \textit{strong evaporation} from \cite{ebtel}. The EM distributions in both the moss regions are strikingly similar and show a monotonically increasing trend from $\log T[\mathrm{K}]=5.15 -6.3$. Using photospheric abundances we obtain a consistent EM distribution for all ions. Comparing the observed and theoretical EM distributions, we find that the observed EM distribution is best explained by the \textit{strong condensation} case (EM$_{con}$), suggesting that a downward enthalpy flux plays an important and possibly dominant role in powering the transition region moss emission. The downflows could be due to unresolved coronal plasma that is cooling and draining after having been impulsively heated. This supports the idea that the hot loops (with temperatures of 3{-}5 MK) seen in the core of active regions are heated by nanoflares. Comment: 17 pages, 4 figures, Accepted for publication in The Astrophysical Journal

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### Keywords

4 figures

\textit{strong condensation}

\textit{strong condensation} case

active region

active regions

Astrophysical Journal

consistent EM distribution

different moss regions

dominant role

downward enthalpy flux

Emission Measure EM$(T)$ distributions

Extreme-Ultraviolet Imaging Spectrometer

full spectral scan

hot loops

moss regions

photospheric abundances

theoretical EM distributions

theoretical transition region EMs

transition region moss emission

unresolved coronal plasma