Hi Phil,

we have addressed this point in the supplementary material of the paper,
giving several reasons why we think it's highly unlikely, and the
non-thermal electrons are a much more natural explanation.

thanks,
Paola


On 10/30/14, 9:54 PM, Philip Judge wrote:


If the sun releases 10^25 erg in 30s in the chromosphere,  as needed by these data, cannot this be just local magnetic heating?  A "chromospheric flare"?

Consider magnetic energy density

E= B^2/ 8pi.

In plage let B be say 300G, then E=3e3.  Then for total energy of 10^25 erg we need  3e21 cm3 and d^3=V gives length  d of 10^7 cm, or 0.1 Mm.  If I use rho= 1e-10 g for mid chromosphere, then the alfven speed v_a is 80 kms and d/v_a is 1.2 sec. Fast.

So I am really puzzled why you appeal to beams at all.  There is certainly nothing in the iris data that I can see could ever be used to give direct evidence for e- beams...  all I can glean from these data is that there is a sudden release of energy under the place where Si IV is formed.

So I am very puzzled...

Philip Judge, Scientist, HAO, NCAR
3037759863
   

On Oct 30, 2014 2:49 PM, "Paola Testa" <ptesta@cfa.harvard.edu> wrote:
Dear all,

you might be interested in the following paper that has just been published on Science:
"Evidence of non-thermal particles in coronal loops heated impulsively by nanoflares"
It can be downloaded from astro-ph: http://arxiv.org/abs/1410.6130 or directly
from the Science pages: http://www.sciencemag.org/content/346/6207/1255724
The abstract is below.

cheers,
Paola


Abstract:
The physical processes causing energy exchange between the Sun’s hot corona and its
cool lower atmosphere remain poorly understood. The chromosphere and transition region
(TR) form an interface region between the surface and the corona that is highly sensitive to
the coronal heating mechanism. High-resolution observations with the Interface Region
Imaging Spectrograph (IRIS) reveal rapid variability (~20 to 60 seconds) of intensity and
velocity on small spatial scales (≲500 kilometers) at the footpoints of hot and dynamic
coronal loops. The observations are consistent with numerical simulations of heating by
beams of nonthermal electrons, which are generated in small impulsive (≲30 seconds)
heating events called “coronal nanoflares.” The accelerated electrons deposit a sizable
fraction of their energy (≲10^25 erg) in the chromosphere and TR. Our analysis provides tight
constraints on the properties of such electron beams and new diagnostics for their
presence in the nonflaring corona.


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