Transition region explosive events: Do they have a coronal counterpart?

¹ Osservatorio Astrofisico di Arcetri, 50125 Firenze, Italy
² Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland

Corresponding author: L. Teriaca, lte@arcetri.astro.it or http://star.arm.ac.uk/preprints/

Received: 22 February 2002
Accepted: 27 May 2002

Abstract

EUV explosive events are a prominent class of phenomena characterizing the solar transition region. Their correct location in the wider frame-work of the outer solar atmosphere can provide important insight on the nature of the transition region itself and its relationship with the hotter corona and the cooler chromosphere. In this paper we present new high-cadence SUMER observations of the “quiet” Sun obtained simultaneously in the mid-transition region N v 1238.8 Å line ( K) and in the coronal Mg x 625 Å line ( K). These observations are aimed at providing information on the behaviour of the coronal plasma during EUV transition region explosive events detected in N v 1238.8 Å. None of the events observed in N v shows any detectable signature in the Mg x line profile or in its integrated intensity. The analysis of 1996 observations obtained simultaneously in N v 1238.8 Å and S ii 1253.8 Å ( K) shows, instead, a weak but clear presence of enhanced wings in the S ii line profile during a series of events observed in N v. These results suggest that EUV explosive events are not directly relevant in heating the corona and are characteristic of structures not obviously connected with the upper corona. The evidence of a chromospheric response suggests that, contrary to some previous suggestions, explosive events have a chromospheric origin.