The Y ohkoh satellite has registered X-ray spectra of two solar Ñares with a linelike feature in the region 400È500 keV. Analysis shows that this feature can be interpreted as gamma-ray lines from excited 7Li and 7Be produced from a ] a reactions. The 7Li production rate in the solar atmosphere is estimated from these observations. The lower limit on the Ñare-produced 7Li abundance on the Sun i...

Solar flares are now observed at all wavelengths from γ-rays to decametre radio waves. They are commonly associated with efficient production of energetic particles at all energies. These particles play a major role in the active Sun because they contain a large amount of the energy released during flares. Energetic electrons and ions interact with the solar atmosphere and produce high-energy X...

We investigate the statistical properties of possible magnetic discontinuities in two solar active regions over the course of several hours. We use linear force-free extrapolations to calculate the three-dimensional magnetic structure in the active regions. Magnetic discontinuities are identified using various selection criteria. Independently of the selection criterion, we identify large numbe...

We report on the results of a systematic study of X-ray flares from low-mass young stellar objects, using two deep exposure Chandra observations of the main region of the ρ Ophiuchi star-forming cloud. From 195 X-ray sources, including class I–III sources and some young brown dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the typical profile of solar and stellar flares,...

In this paper, a machine learning-based system that could provide automated short-term solar flares prediction is presented. This system accepts two sets of inputs: McIntosh classification of sunspot groups and solar cycle data. In order to establish a correlation between solar flares and sunspot groups, the system explores the publicly available solar catalogues from the National Geophysical D...

Solar hard X-ray flares can expose astronauts on lunar and deep space extravehicular activities (EVAs) to dangerous acute biological doses. We combine calculations of radiative transfer through shielding materials with subsequent transfer through tissue to show that hazardous doses, taken as ≥ 0.1 Gy, should occur with a probability of about 10% per 100 hours of accumulated EVA inside current s...

Recent progress in solar Hard X-ray (HXR) observations with RHESSI data and methods for spectral inversion allow us to study model-independent mean electron flux spectra in solar flares. We report several hard X-ray events observed by RHESSI in which the photon spectra I(ǫ) are such that the inferred source mean electron spectra are not consistent with the standard model of collisional transpor...

A time series of soft X-ray emission observed on 1974-2007 years (GOES) is analyzed. We show that in the periods of high solar activity 1977-1981, 19881992, 1999-2003 the energy statistics of soft X-ray solar flares for class M and C is well described by a FARIMA time series with Pareto innovations. The model is characterized by two effects. One of them is a long-range dependence (longterm memo...

Mid-term quasi-periodicities in solar coronal mass ejections (CMEs) during the most recent solar maximum cycle 23 are reported here for the first time using the fouryear data (February 5, 1999 to February 10, 2003) of the Large Angle Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). In parallel, mid-term quasi-periodicities in solar X-ray flares (class >M5...