A coronal explosion on the flare star CN Leonis
Abstract
We present simultaneous high-temporal and high-spectral resolution observations of the nearby flare star CN Leo at optical and soft X-ray wavelengths. During our observing campaign a major flare occurred, raising the star's instantaneous energy output by almost three orders of magnitude. The flare shows the often observed impulsive behavior, with a rapid rise and slow decay in the optical and a broad soft X-ray maximum about 200 seconds after the optical flare peak. In addition to this usually encountered flare phenomenology we find, however, an extremely short (τ _dec ≈ 2 s) soft X-ray peak, which is very likely of thermal, rather than nonthermal nature and coincides temporally with the optical flare peak. While at hard X-ray energies nonthermal bursts are routinely observed on the Sun at flare onset, thermal soft X-ray bursts on time scales of seconds have never been observed in a solar, nor stellar context. Time-dependent, one-dimensional hydrodynamic modeling of this event requires an extremely short energy deposition time scale τ _dep of a few seconds to reconcile theory with observations, thus suggesting that we are witnessing the results of a coronal explosion on CN Leo. Thus the flare on CN Leo provides the opportunity to observationally study the physics of the long-sought “micro-flares” thought to be responsible for coronal heating.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- April 2008
- DOI:
- 10.1051/0004-6361:20079017
- arXiv:
- arXiv:0801.3752
- Bibcode:
- 2008A&A...481..799S
- Keywords:
-
- X-rays: stars;
- stars: individual: CN Leo;
- stars: flares;
- stars: coronae;
- stars: activity;
- Astrophysics
- E-Print:
- 7 pages, accepted by A&