EUV signatures of small EUV signatures of small scale heating in loopsscale heating in loops

Susanna ParentiSusanna Parenti

SIDC-Royal Observatory of Belgium, BeSIDC-Royal Observatory of Belgium, Be

Nanoflares & NanoflaresNanoflares & Nanoflares

Hard X-ray and EUV nanoflaresHard X-ray and EUV nanoflares– Observed small scale Observed small scale

brighteningsbrightenings

Nanoflares in loopsNanoflares in loops– Not resolved. The QS EUV Not resolved. The QS EUV

brightenings may be due to a brightenings may be due to a bunch of nanoflaresbunch of nanoflares

– Loop made of collection of Loop made of collection of strands: multi-thermal structurestrands: multi-thermal structure

Parnell et al. 2000

The frequency distribution of energyThe frequency distribution of energy

Hypothesis Hypothesis :: the frequency distribution of the energy derived the frequency distribution of the energy derived from the observed (flare) emission is the same as the frequency from the observed (flare) emission is the same as the frequency

distribution of heating eventsdistribution of heating events!!

Plasma responsePlasma response

?

Forward-modelingForward-modelingBuchlin et al. 2003

Small scale heating signatureSmall scale heating signature

The objective :The objective :

To verify if and under which conditionsif and under which conditions the statistical properties of the heating are preserved in the radiative (EUV) and thermal energies

Application: multi-stranded coronal loop

The modelsThe models

Heating model: nanoflares are the result of energy dissipation originating from turbulent fluctuations in the photosphere (Einaudi et al. ’96, Buchlin et al, 2003). The number of events is distributed in energy as a power law of = - 1.6.

The cooling model (Cargill ‘94): Conduction phase, Conduction phase, R R > > C C :: p = const; strand subject to

subsonic plasma evaporation Radiative phase, Radiative phase, R R < < C C :: TeNe

2 (Serio et al. ’91, Jakimiec et al. ‘92)the strand is subject to draining (Antiochos ‘80)

Buchlin et al. 2003

Results: the history of Ne and Te in each strand are used for the statistical analysis of the whole loop system.

Results: (Parenti et al. 2006, ApJ, 651, 1219 )

Thermal energy: the statistical properties of the heating function can be better recovered if the loop filling factor is small and the dominant cooling process is thermal conduction.

Synthetic spectra in EUV : similar results but

different behaviour of lines formed at different T

best candidates are the lines which form at T > 3 MK

radiation

conduction

New results:New results:

Statistical distribution of EUV lines belonging to the Statistical distribution of EUV lines belonging to the Li Li isoelectronic sequenceisoelectronic sequence. Is there any difference with . Is there any difference with previous results? previous results?

Comparison of PDF of EUV emissions from Comparison of PDF of EUV emissions from wide and wide and narrow band instrumentsnarrow band instruments..

Parenti & Young 2008

Set up the simulationSet up the simulation

Multi-strand loop (2000)Multi-strand loop (2000) Nanoflare heating function Nanoflare heating function

with a power law distribution with a power law distribution of index of index αα = -1.7 = -1.7

EIS, SUMER & EITEIS, SUMER & EIT

Parenti & Young 2008

radiation conduction

Narrow band instrumentsNarrow band instruments

Parenti & Young 2008

logT =

5.8logT

= 6.1

Li-likeInput: heating

energy

Wide-narrow band instrumentsWide-narrow band instruments

Parenti & Young 2008

EIT SUMER & EIS

Input: heating energy

The hot linesThe hot lines

Input: heating energy

ConclusionConclusion

The shape of the PDF of EUV lines depends on the iso-The shape of the PDF of EUV lines depends on the iso-electronic sequence of the ion.electronic sequence of the ion. Li-like lines do not look suitable for this diagnosticLi-like lines do not look suitable for this diagnostic

Wide-band instruments affect the PDF shape of the EUV Wide-band instruments affect the PDF shape of the EUV lineslines

Confirmed that the high T lines better preserve the Confirmed that the high T lines better preserve the properties of the heating function (also Li-like)properties of the heating function (also Li-like)

Work useful for SDO, Solar Orbiter data. The high T Work useful for SDO, Solar Orbiter data. The high T channels may bring insight on the coronal heating channels may bring insight on the coronal heating statistical properties.statistical properties.

Backup slidesBackup slides

Method : numerical model for a loop system

transport, accumulation & dissipation of E RMHD

plasma response (Ne, Te) 0D hydrodynamic

radiative losses (I) CHIANTI

Thermal E and EUV synthetic spectra to be compared to Thermal E and EUV synthetic spectra to be compared to observationsobservations

system: simultaneous characterization of n. strands >> 1 unresolved

MethodMethod

superposition effect

Small scale heating: TurbulenceSmall scale heating: Turbulence Nanoflares may be the result of energy dissipation originating from turbulent fluctuations in the photosphere. The energy propagates in the corona through Alfvén waves (Einaudi et al. ’96, Buchlin et al, 2003).

The number of events is distributed in energy as a power law of index = - 1.6.

Buc

hlin

et a

l. 20

03

Conduction phase : Conduction phase : R R > > CC

Analytic solutions of Antiochos & Sturrock 1978 p = const; strand subject to subsonic plasma evaporation

Radiative phase : Radiative phase : R R < < CC

TeNe2 (Serio et al. ’91, Jakimiec et al. ‘92)

the strand subject to draining (Antiochos ‘80)

The cooling modelThe cooling model Cargill ’94

nano= Q/(E A n) ; C Ne L2/ Te5/2 ; R Te

1-

/ Ne Aim: to study the behaviour of the plasma parameters in the whole loop system as a function of Q, L, A.

Results: the history of Ne and Te in each strand to be used for the statistical analysis of the whole loop system.

Total thermal energyTotal thermal energy

Input: heating energy

Buchlin et al. 2003

The PDF of the loop thermal energy turns out to be a power law The power law index can change depending on the sub-loop geometry.

ff: 0.52 0.013 0.06

Output: thermal energy

Parenti et al. 2006