Nanoflare heating of coronal loops: hydrodynamic response and observational consequences

Abstract

The plasma response inside a semicircular coronal loop heated by nanoflares is examined. The loop is thermally and gravitationally stratified. The losses due to thermal conduction and radiation are balanced by localised energy pulses randomly deposited along the loop. The initial stage of the loop evolution during which the temperature along the loop gradually increases from chromospheric to coronal values is completed about 20 minutes after the start of the heating. The random heating produces a thin transition region which is in a continuous motion. The profiles of the C IV, O VI, Ne VIII and Mg X resonance lines, which have peak formation temperatures covering the upper transition region and lower corona, are synthesised. The line shifts and the average shifts are calculated and compared with the observations. It is shown that the nanoflare heating mechanism may reproduce the observed dynamics of the transition region lines. The calculated and previously measured average Doppler shift values are in good agreement for the studied spectral lines except for the C IV line. Possible reasons for this discrepancy are discussed. The study also shows that the nanoflares could contribute to the oscillation power often seen in the mHz ranges. The power peak of the resulting oscillations is near 2 mHz.