Research Note

Properties of multistranded, impulsively heated hydrodynamic loop models

¹ INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese (TO), Italy
e-mail: sur@oact.inaf.it
² INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
³ Dipartimento di Fisica e Astronomia – Sezione Astrofisica, Università di Catania, via S. Sofia 78, 95123 Catania, Italy

Received: 19 January 2011
Accepted: 8 February 2013

Abstract

Aims. We investigate the capability of multistranded loop models subject to nanoflare heating to reproduce the properties recently observed in coronal loops at extreme ultraviolet (EUV) wavelengths.

Methods. One-dimensional hydrodynamic simulations of magnetic loop strands were performed with an impulsive, footpoint-localised heating, with a moderate asymmetry between the two loop halves that was produced either by a sequence of identical nanoflares with a given cadence time t_C or by a single energy pulse. The temporal evolution of the emission of a multistranded loop was modelled by simply combining the results of independent single-strand simulations, neglecting any spatial interaction among the strands, and was compared with TRACE and SDO/AIA light curves. The density excess with respect to hydrostatic equilibrium (the ψ factor) was evaluated with the filter-ratio technique.

Results. Both loop models exhibit a density excess compared with hydrostatic equilibrium models, which agrees well with the observed values (1 ≲ ψ ≲ 12). However, in the single-pulse model the light curve and density excess maxima do not match. On the other hand, the models with a sequence of nanoflares predict strong emission at lower temperatures that cannot be reconciled with the available observations.