1. EUV signatures of small scale heating in loops Susanna Parenti SIDC-Royal Observatory of Belgium, Be

2. Nanoflares & Nanoflares Hard X-ray and EUV nanoflares Hard X-ray and EUV nanoflares –Observed small scale brightenings Nanoflares in loops Nanoflares in loops –Not resolved. The QS EUV brightenings may be due to a bunch of nanoflares –Loop made of collection of strands: multi-thermal structure Parnell et al. 2000

3. The frequency distribution of energy Hypothesis : the frequency distribution of the energy derived from the observed (flare) emission is the same as the frequency distribution of heating events ! Plasma response ? Forward-modeling Buchlin et al. 2003

4. Small scale heating signature The objective : if and under which conditions To verify if and under which conditions the statistical properties of the heating are preserved in the radiative (EUV) and thermal energies Application: multi-stranded coronal loop

5. The 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,  R >  C : Conduction phase,  R >  C : p = const; strand subject to subsonic plasma evaporation Radiative phase,  R <  C : Radiative phase,  R <  C : T e  N e 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.

6. 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 radiationconduction

7. New results: Statistical distribution of EUV lines belonging to the Li isoelectronic sequence. Is there any difference with previous results? Statistical distribution of EUV lines belonging to the Li isoelectronic sequence. Is there any difference with previous results? Comparison of PDF of EUV emissions from wide and narrow band instruments. Comparison of PDF of EUV emissions from wide and narrow band instruments. Parenti & Young 2008

8. Set up the simulation Multi-strand loop (2000) Multi-strand loop (2000) Nanoflare heating function with a power law distribution of index α = -1.7 Nanoflare heating function with a power law distribution of index α = -1.7 EIS, SUMER & EIT EIS, SUMER & EIT Parenti & Young 2008 radiationconduction

9. Narrow band instruments Parenti & Young 2008 logT = 5.8 logT = 6.1 Li-like Input: heating energy

10. Wide-narrow band instruments Parenti & Young 2008 EITSUMER & EIS Input: heating energy

11. The hot lines Input: heating energy

12. Conclusion The shape of the PDF of EUV lines depends on the iso- electronic sequence of the ion. The shape of the PDF of EUV lines depends on the iso- electronic sequence of the ion. Li-like lines do not look suitable for this diagnostic Li-like lines do not look suitable for this diagnostic Wide-band instruments affect the PDF shape of the EUV lines Wide-band instruments affect the PDF shape of the EUV lines Confirmed that the high T lines better preserve the properties of the heating function (also Li-like) Confirmed that the high T lines better preserve the properties of the heating function (also Li-like) Work useful for SDO, Solar Orbiter data. The high T channels may bring insight on the coronal heating statistical properties. Work useful for SDO, Solar Orbiter data. The high T channels may bring insight on the coronal heating statistical properties.

13. Backup slides

14. Method : numerical model for a loop system transport, accumulation & dissipation of E RMHD plasma response (N e, T e ) 0D hydrodynamic radiative losses (I) CHIANTI Thermal E and EUV synthetic spectra to be compared to observations Thermal E and EUV synthetic spectra to be compared to observations system: simultaneous characterization of n. strands >> 1 unresolvedMethod superposition effect

15. Small 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. Buchlin et al. 2003

16. Conduction phase :  R >  C Conduction phase :  R >  C Analytic solutions of Antiochos & Sturrock 1978 p = const; strand subject to subsonic plasma evaporation Radiative phase :  R <  C Radiative phase :  R <  C T e  N e 2 (Serio et al. ’91, Jakimiec et al. ‘92) the strand subject to draining (Antiochos ‘80) The cooling model Cargill ’94  nano = Q/(E A n);  C  N e L 2 / T e 5/2 ;  R  T e 1-  / N e  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 N e and T e in each strand to be used for the statistical analysis of the whole loop system.

17. Total 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 0.0130.06 Output: thermal energy Parenti et al. 2006