G. A. Matveev

Solar flares registered by the IRIS spectrometer onboard the CORONAS-F satellite: Peculiarities of the X-ray emission

The X-ray spectrometer IRIS was designed to register the fluxes of quanta with energies ranging from 2 to 250 keV in various time-resolution modes: 0.01, 1.0, and 2.5 s in 4, 64, and 12 channels, respectively. Owing to the high instrument sensitivity, individual spikes of tens of milliseconds can be distinguished in the time structure of the X-ray flare emission. The time spectral analysis carried out for the X-ray emission of a number of registered flares points to the presence of a quasiperiodic structure with characteristic times of the same order. For the flares of December 19, 2001, and August 10, 2002, the process of energy release has been considered with a 1-s time resolution, and its periodic character has been revealed. For the flare of December 19, 2001, the energy spectra of the hard X-ray emission have been simulated by thermal and nonthermal models. It has been shown that the both models can describe this emission.

On the Reconstruction of the Energy Distribution of Electrons Accelerated in Solar Flares

A technique for reconstructing energy spectra of electrons accelerated in solar flares is suggested that is based on the rigorous solution of the inverse problem considering their X-ray bremsstrahlung. Model calculations are made for various spectra, and it is proved that this technique makes it possible to find the electron energy distribution in real flare events. The energy distribution of high-energy electrons accelerated in the solar flare observed on July 26, 2002, is reconstructed. It is shown that the hard X-ray spectrum of the flare may result from the bremsstrahlung of three groups of high-energy electrons.

Peculiarities of X-ray emission of the solar flare on 29 October 2002

[1] Time structure of the soft and hard X-ray emission of the solar flare on 29 October 2002 is studied. The flare began at 2148:49 UT and was measured by the IRIS spectrometer on board the CORONAS-F spacecraft. High sensitivity of the device made it possible to detect in the flare X-ray emission a pulse structure with timescale of the order of tens of milliseconds. Similarly, spike structure was observed on board of Compton Gamma Ray Observatory. A quasiperiodic structure with a magnitude of the order of 10 s was revealed by means of spectral time analysis. This structure can be explained by magnetohydrodynamic sausage-mode oscillations generated in the flare loop with the characteristic parameters of the plasma of the coronal region of the solar atmosphere. The evolution of the energetic spectrum of the hard X-ray emission of this flare with the resolution of 1 s during the entire event is studied.

Spectrometer IRIS: Investigation of the Time Structure and Energy Spectra of X-Ray Emission from Solar Flares

The research program underlying the IRIS experiment (Russian acronym for Investigation of Solar X-Ray Emission) encompasses investigation of the characteristics of X-ray emission from solar flares and of their precursors in the 2–200-keV range, which would form a basis for development of physical models describing the process of buildup and explosive release of energy in a solar flare, as well as accumulation of experimental data to serve in devising techniques for forecasting the solar flare activity

Soft X-rays in the 00:18 UT solar flare on April 22, 1994

Abstract The IRIS spectrometer employs scintillation and proportional counters with large-sized windows. It offers possibility for measuring X-ray flux of flare precursors and micro- and nanoflares as well as studying fine time structures in hard X-rays during the impulsive phase of strong solar flares. Characteristics of the spectrometer (time resolution, number of energy channels, sensitivity to soft X-rays) are automatically changeable depending on measured X-ray flux. The essential properties of the IRIS spectrometer are listed in Table 1 (for detailed description see Kocharov et al , 1989, and Charikov et al , 1997).

Energy release in the 00:18 UT solar flare on April 22, 1994☆

Abstract We discuss the energy release process in a solar flare. The onset of this flare in soft X-rays was detected at 00:18 UT on April 22nd, 1994, by the IRIS X-ray spectrometer, which was a component of the scientific payload in the international complex research project on solar-terrestrial phenomena on board the CORONAS-I automatic orbital station. An analysis of energy spectra and time profiles of soft X-ray radiation indicates that no usual expansion of flaring volume occurred at the decay of this flare. On the contrary, thermal insulation of the hot plasma could be in effect.

Characteristics of solar X-ray radiation in March and April 1994 obtained in the IRIS experiment on board KORONAS-I

The first brief report on the results obtained in the IRIS experiment is presented. The IRIS instrument is an X-ray spectrometer based on proportional and scintillation counters designed for the measurement of solar X-ray radiation in the 2–200 keV range. Data on the 12 flares observed in March and April 1994 are reported, and examples of the flare radiation spectra are given.