[Loops] New paper on evidence of hot plasma in non-flaring active region loops

[Eric Priest]

Fabio
Many thanks for that - peter cargillhad told me about it and so I have
been looking out for it - -super - well done
Eric

On Tue, Apr 7, 2009 at 10:21 AM, Reale Fabio <reale at astropa.unipa.it> wrote:
> Dear all,
>    please find on Astro-PH at the following link:
>
> http://arxiv.org/abs/0904.0878
>
> a new paper that supports the detection of widespread hot plasma in
> non-flaring active regions from Hinode/XRT observations (see the
> abstract below). The paper has just been accepted for publication on
> ApJ. We have devoted an Appendix to the issue of filter calibration.
> Thank you for your attention
> Best regards
> Fabio Reale
>
> Evidence of widespread hot plasma in a non-flaring coronal active region
> from Hinode/XRT
> Authors:   Fabio Reale, Paola Testa, James A. Klimchuk, Susanna Parenti
>
>    Abstract: Nanoflares, short and intense heat pulses within spatially
>    unresolved magnetic strands, are now considered a leading candidate
>    to solve the coronal heating problem. However, the frequent
>    occurrence of nanoflares requires that flare-hot plasma be present
>    in the corona at all times. Its detection has proved elusive until
>    now, in part because the intensities are predicted to be very faint.
>    Here we report on the analysis of an active region observed with
>    five filters by Hinode/XRT in November 2006. We have used the filter
>    ratio method to derive maps of temperature and emission measure both
>    in soft and hard ratios. These maps are approximate in that the
>    plasma is assumed to be isothermal along each line-of-sight.
>    Nonetheless, the hardest available ratio reveals the clear presence
>    of plasma around 10 MK. To obtain more detailed information about
>    the plasma properties, we have performed Monte Carlo simulations
>    assuming a variety of non-isothermal emission measure distributions
>    along the lines-of-sight. We find that the observed filter ratios
>    imply bi-modal distributions consisting of a strong cool (log T ~
>    6.3-6.5) component and a weaker (few percent) and hotter (6.6 < log
>    T < 7.2) component. The data are consistent with bi-modal
>    distributions along all lines of sight, i.e., throughout the active
>    region. We also find that the isothermal temperature inferred from a
>    filter ratio depends sensitively on the precise temperature of the
>    cool component. A slight shift of this component can cause the hot
>    component to be obscured in a hard ratio measurement. Consequently,
>    temperature maps made in hard and soft ratios tend to be
>    anti-correlated. We conclude that this observation supports the
>    presence of widespread nanoflaring activity in the active region.
>
>
>
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