Modeling an X-ray flare on Proxima Centauri: Evidence of two flaring loop components and of two heating mechanisms at work^*

¹ Dipartimento di Scienze Fisiche & Astronomiche, Sezione di Astronomia, Università di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy e-mail: peres@astropa.unipa.it
² Paul Scherrer Institut, Würenlingen & Villigen, 5232 Villigen PSI, Switzerland e-mail: guedel@astro.phys.ethz.ch
³ Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA e-mail: audard@astro.columbia.edu

Corresponding author: F. Reale, reale@astropa.unipa.it

Received: 30 June 2003
Accepted: 2 December 2003

Abstract

We model in detail a flare observed on Proxima Centauri with the EPIC-PN on board XMM-Newton at high statistics and high time resolution and coverage. Time-dependent hydrodynamic loop modeling is used to describe the rise and peak of the light curve, and a large fraction of the decay, including its change of slope and a secondary maximum, over more than 2 h. The light curve, the emission measure and the temperature derived from the data allow us to constrain the loop morphology and the heating function and to show that this flare can be described with two components: a major one triggered by an intense heat pulse injected in a single flaring loop with half-length ≈ cm, the other one by less intense heat pulses released about 1/2 h after the first one in related loop systems, probably arcades, with the same half-length. The heat functions of the two loop systems appear very similar: an intense pulse located at the loop footpoints followed by a low gradual decay distributed in the coronal part of the loop. The latter result and the similarity to at least one solar event (the Bastille Day flare in 2000) indicate that this pattern may be common to solar and stellar flares.