X-ray flares in Orion low-mass stars

M. Caramazza, E. Flaccomio, G. Micela, F. Reale, S. J. Wolk, E. D. Feigelson

Research output: Contribution to journalArticlepeer-review

56 Scopus citations


Context. X-ray flares are common phenomena in pre-main sequence stars. Their analysis gives insights into the physics at work in young stellar coronae. The Orion Nebula Cluster offers a unique opportunity to study large samples of young low mass stars. This work is part of the Chandra Orion Ultradeep project (COUP), an ∼ 10 day long X-ray observation of the Orion Nebula Cluster (ONC). Aims. Our main goal is to statistically characterize the flare-like variability of 165 low mass (0.1-0.3 M) ONC members in order to test and constrain the physical scenario in which flares explain all the observed emission. Methods. We adopt a maximum likelihood piece-wise representation of the observed X-ray light curves and detect flares by taking into account both the amplitude and time derivative of the count-rate. We then derive the frequency and energy distribution of the flares. Results. The high energy tail of the energy distribution of flares is well described by a power-law with index ∼2.2. We test the hypothesis that light curves are built entirely by overlapping flares with a single power law energy distribution. We constrain the parameters of this simple model for every single light curve. The analysis of synthetic light curves obtained from the model indicates a good agreement with the observed data. Comparing low mass stars with stars in the mass interval (0.9-1.2 M), we establish that, at ∼1 Myr, low mass and solar mass stars of similar X-ray luminosity have very similar flare frequencies. Conclusions. Our observational results are consistent with the following model/scenario: the light curves are entirely built by overlapping flares with a power-law intensity distribution; the intense flares are individually detected, while the weak ones merge and form a pseudo-quiescent level, which we indicate as the characteristic level.

Original languageEnglish (US)
Pages (from-to)645-654
Number of pages10
JournalAstronomy and Astrophysics
Issue number2
StatePublished - Aug 2007

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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