Magnetic flaring in the pre-main sequence Sun and implications for the early solar system

To address the role of energetic processes in the solar nebula, we provide a detailed characterization of magnetic flaring in stellar analogs of the pre-main sequence Sun based on two 0.5-day observations of analogs of the young Sun in the Orion Nebula Cluster obtained with the Chandra X-ray Observatory. The sample consists of 43 stars with masses 0.7-1.4 M⊙ and ages < 0.3 to ≃ 10 My. We find the X-ray luminosities measured in the 0.5 − 8 keV band are strongly elevated over main sequence levels with average < logLx >= 30.3 erg s −1 and < logLx/L⋆ >= −3.9. The X-ray emission is strongly variable within our exposures in nearly all solar analogs; about 30 flares with 29.0 < logLx(peak) < 31.5 erg s −1 on timescales from 0.5 to > 12 hours are seen during the Chandra observations. Analogs of the ≤ 1 My old pre-main sequence Sun exhibited X-ray flares that are 10 times more powerful and 10 times more frequent than the most powerful flares seen on the contemporary Sun. Radio observations indicate that acceleration of particles to relativistic energies is efficient in young stellar flares. Extrapolating the solar relationship between X-ray luminosity and proton fluence, we infer that the young Sun exhibited a 10-fold enhancement in energetic protons compared to contemporary levels. Unless the flare geometries are unfavorable, this inferred proton flux on