[Loops] new evidence for nanoflaring in active regions

[Fabio Reale]

Dear friends,
    please find in the following links (and abstracts) to two ApJ preprints (one main Journal, published, one Letter, in press) providing support for nanoflare activity in the core of active regions. 0D and 1D multi-strand modeling are used in chain to show that pixel EUV light curves are well-explained by storms of nanoflares and that the model nanoflares produce trends of fluctuations along the loops, which are confirmed by AIA observations. The first author is Edris Tajfirouze, PhD student at the University of Palermo.
Thank you for your attention
Best regards
Fabio


Time-resolved emission from bright hot pixels of an active region observed in the EUV band with SDO/AIA and multi-stranded loop modeling

E. Tajfirouze, F. Reale, A. Petralia, P. Testa

http://arxiv.org/abs/1510.07524



EUV flickering of solar coronal loops: a new diagnostic of coronal heating

E. Tajfirouze, F.Reale, G. Peres, P. Testa

http://arxiv.org/abs/1601.03935



Time-resolved emission from bright hot pixels of an active region observed in the EUV band with SDO/AIA and multi-stranded loop modeling

E. Tajfirouze, F. Reale, A. Petralia, P. Testa

Evidence for small amounts of very hot plasma has been found in active regions and might be the indication of an impulsive heating, released at spatial scales smaller than the cross section of a single loop. We investigate the heating and substructure of coronal loops in the core of one such active region by analyzing the light curves in the smallest resolution elements of solar observations in two EUV channels (94 A and 335 A) from the Atmospheric Imaging Assembly on-board the Solar Dynamics Observatory. We model the evolution of a bundle of strands heated by a storm of nanoflares by means of a hydrodynamic 0D loop model (EBTEL). The light curves obtained from the random combination of those of single strands are compared to the observed light curves either in a single pixel or in a row of pixels, simultaneously in the two channels and using two independent methods: an artificial intelligent system (Probabilistic Neural Network, PNN) and a simple cross-correlation technique. We explore the space of the parameters to constrain the distribution of the heat pulses, their duration and their spatial size, and, as a feedback on the data, their signatures on the light curves. From both methods the best agreement is obtained for a relatively large population of events (1000) with a short duration (less than 1 min) and a relatively shallow distribution (power law with index 1.5) in a limited energy range (1.5 decades). The feedback on the data indicates that bumps in the light curves, especially in the 94 A channel, are signatures of a heating excess that occurred a few minutes before.


EUV flickering of solar coronal loops: a new diagnostic of coronal heating

E. Tajfirouze, F.Reale, G. Peres, P. Testa

A previous work of ours found the best agreement between EUV light curves observed in an active region core (with evidence of super-hot plasma) and those predicted from a model with a random combination of many pulse-heated strands with a power-law energy distribution. We extend that work by including spatially resolved strand modeling and by studying the evolution of emission along the loops in the EUV 94 A and 335 A channels of the Atmospheric Imaging Assembly on-board the Solar Dynamics Observatory. Using the best parameters of the previous work as the input of the present one, we find that the amplitude of the random fluctuations driven by the random heat pulses increases from the bottom to the top of the loop in the 94 A channel and, viceversa, from the top to the bottom in the 335 A channel. This prediction is confirmed by the observation of a set of aligned neighbouring pixels along a bright arc of an active region core. Maps of pixel fluctuations may therefore provide easy diagnostics of nano-flaring regions.