[Loops] new paper on a test of MCMC DEM reconstruction

[Paola Testa]

Dear all,

our paper on testing the MCMC DEM reconstruction method by using 3D MHD 
simulations has just been accepted for publication on ApJ. You can find 
a preprint at:
http://folk.uio.no/bdp/papers/3dEMD_ptesta.pdf

(It will also appear soon on astro-ph but in an abridged version due to 
the length of the paper and astro-ph restrictions on submission size)

Please find the title and abstract below.

cheers,
Paola



Title: "Investigating the reliability of coronal emission measure distribution
   diagnostics using 3D radiative MHD simulations"

Authors: Paola Testa, Bart De Pontieu, Juan Martinez-Sykora,
   Viggo Hansteen, Mats Carlsson

Abstract:
  Determining the temperature distribution of coronal plasmas can provide
stringent constraints on coronal heating. Current observations with the Extreme
ultraviolet Imaging Spectrograph onboard Hinode and the Atmospheric Imaging
Assembly onboard the Solar Dynamics Observatory provide diagnostics of the
emission measure distribution (EMD) of the coronal plasma.
   Here we test the reliability of temperature diagnostics using 3D radiative
MHD simulations. We produce synthetic observables from the models, and apply
the Monte Carlo Markov chain EMD diagnostic. By comparing the derived EMDs with
the ``true'' distributions from the model we assess the limitations of the
diagnostics, as a function of the plasma parameters and of the signal-to-noise
of the data.
   We find that EMDs derived from EIS synthetic data reproduce some general
characteristics of the true distributions, but usually show differences from
the true EMDs that are much larger than the estimated uncertainties suggest,
especially when structures with significantly different density overlap along
the line-of-sight. When using AIA synthetic data the derived EMDs reproduce the
true EMDs much less accurately, especially for broad EMDs. The differences
between the two instruments are due to the: (1) smaller number of constraints
provided by AIA data, (2) broad temperature response function of the AIA
channels which provide looser constraints to the temperature distribution.
   Our results suggest that EMDs derived from current observatories may often
show significant discrepancies from the true EMDs, rendering their
interpretation fraught with uncertainty. These inherent limitations to the
method should be carefully considered when using these distributions to
constrain coronal heating.