Transient brightenings of interconnecting loops

Abstract

We present two alternative interpretations of the sudden X-ray brightenings observed in loops that interconnect active regions. A fast tearing mode may be excited in those newly formed interconnecting loops within which sufficient magnetic free energy is stored to drive the mode. Alternatively anomalous Joule heating driven by an inductive electric field parallel to the magnetic field varying on a time scale of order of a minute may cause the brightenings. We argue that it is plausible that the fast tearing mode may be the cause of brightenings in the young newly formed interconnecting loops, whereas the anomalous Joule heating might occur in old loop connections when an external disturbance propagates through them.