The SPR-N polarimeter onboard the CORONAS-F satellite allows the X-ray polarization degree to be measured in energy ranges of 20–40, 40–60, and 60–100 keV. To measure the polarization, the method based on the Thompson scattering of solar X-ray photons in beryllium plates was used; the scattered photons were detected with a system of six CsI(Na) scintillation sensors. During the observation period from August 2001 to January 2005, the SPR-N instrument detected the hard X-rays of more than 90 solar flares. The October 29, 2003, event showed a significant polarization degree exceeding 70% in channels of E = 40–60 and 60–100 keV and about 50% in the 20-to 40-keV channel. The time profile of the polarization degree and the projection of the polarization plane onto the solar disk were determined. For 25 events, the upper limits of the part of polarized X-rays were estimated at 8 to 40%. For all the flares detected, time profiles (with a resolution of up to 4 s), hard X-ray radiation fluxes, and spectral index estimates were obtained.

We present new observational data on the phenomena of extremely high activity on the Sun and in the heliosphere that took place in October–November 2003. A large variety of solar and heliospheric parameters give evidence that the interval under consideration is unique over the entire observation time. Based on these data, comparing them with similar situations in the past and using available theoretical concepts, we discuss possible cause-and-effect connections between the processes observed. The paper includes the first results and conclusions derived by the collaboration “Solar Extreme Events-2003” organized in Russia for detailed investigations of these events. As a result of our consideration, it is beyond question that the physical causes of solar and heliospheric phenomena in October–November 2003 are not exclusively local and do not belong only to the active regions and solar atmosphere above them. The energy reservoirs and driving forces of these processes have a more global nature. In general, they are hidden from an observer, since ultimately their sources lie in the subphotospheric layers of the Sun, where changes that are fast and difficult to predict can sometimes take place (and indeed they do). Solar flares can serve as sufficiently good tracers of these sudden changes and reconstructions on the Sun, although one can still find other diagnostic indicators among the parameters of magnetic fields, motions of matter, and emission characteristics.

The first results of the experiment with the SPR-N hard X-ray (20–100 keV) polarimeter onboard the Coronas-F observatory (the experiment started on August 15, 2001) are presented. Hard X-ray radiation was detected from several solar flares. The spectral and temporal parameters were determined and the polarization was estimated. Comparison with the GOES observations of thermal X-ray radiation shows that hard X-ray bursts occur at the growth phase of the thermal radiation and that they are associated with the bremsstrahlung of energetic electrons precipitating into the solar atmosphere.

The paper describes the main characteristics of the X-ray optical elements (multilayer spherical and aspherical mirrors and diffraction gratings for the 13-30 nm XUV spectral region, Bragg crystal spherical mirrors for the 0.18 and 0.84 m soft X-ray spectral regions) manufactured for the TEREK-C solar XUV telescope array and the RES-C solar spectroheliograph. The TEREK-C and RES-C instruments were placed aboard the CORONAS-I satellite which was launched on March 2, 1994. The testing procedures and results of laboratory tests in X-ray spectral range are also presented.

The paper describes instruments for solar imaging XUV spectroscopy -- the TEREK-C telescope array and the RES-C spectroheliograph mounted on board the Russian-Ukrainian CORONAS-I satellite (launched on March 2, 1994). The CORONAS project is carried out under scientific guidance of Prof. V.N. Oraevsky, director of the IZMIRAN (Troitsk, Moscow region, Russia) -- leading institute of this project. The instruments were intended to obtain high resolution solar images and spectra from the transition region and the corona of the Sun within the temperature range of 105 - 107 K. The optical design of the TEREK telescope array includes two Herschelian XUV-telescopes with Mo-Si multilayer mirrors: the first one with 3 whole-Sun spectral channels (reflection peaks at (lambda) equals 13.2, 17.5 and 30.4 nm, angular scale 4.7'), the second channel -- with 4 mirrors, each covering 1/4 of the Sun ((lambda) equals 17.5 nm, angular scale 1'). The RES-C spectroheliograph has five measuring channels with a whole-Sun field of view: two XUV channels with orthogonal dispersion planes, equipped with grazing incidence gratings and multilayer mirrors to obtain high resolution spectral images in the 19.2 - 20.1 nm band (spectral resolution 2 (DOT) 10-4 nm/pix, angular scale 4.5'), two MgXII channels having narrow-band imaging systems with orthogonal dispersion planes for the 0.841 - 0.843 nm spectral band, equipped with Bragg crystal spherical mirrors, and one FeXXV imaging system with a ring Bragg crystal mirror for the 0.184 - 0.188 nm spectral band. Two types of image detectors were designed with the use of CCD-matrices (1024 X 1152 elements) and image intensifiers (with an open microchannel plate and a luminescent converter). The paper presents a detailed description of the overall structure, electronic design and the main characteristics of the instruments, preliminary results of flight functioning of the TEREK-C and RES-C instruments and examples of the images and spectra of the Sun obtained in the experiment.

The method of imaging XUV spectroscopy was used to study plasma in the transition layer and inner corona of the Sun with temperatures 105–107 K in the TEREK and RES experiments on board KORONAS-I. The observations were carried out in the period from March 12 to July 5, 1994. The spectral images and their correlation with the YOHKOH X-ray images and groundbased observations are important for the study of the physical conditions and modeling of the bulk processes in the quiet Sun plasma, including active regions, corona holes, and overlimb structures.

The TEREK-K telescope and the RES-K spectroheliometer aboard the KORONAS-I spacecraft were used to study the solar upper atmosphere by X-ray and XUV imaging spectroscopy in the 0.84-30.4 nm band. More than 2000 images of the Sun were taken between March 12 and July 5, 1994. New data on parameters of the solar plasma were obtained in the temperature range 10(5)-10(7) K and at heights from the transition zone to the upper corona. A description of the instruments and a summary of observing sessions are given.

A neutron tomography technique with a coordinate resolution of several tens of micrometers has been developed. Our results indicate that the technique resolves details with dimensions less than 100μm and measures a linear attenuation of less than similar 0.1 cm−1. Tomograms can be reconstructed using incomplete data. Limits on the resolution of the restored pattern are analyzed, and ways to improve the sensitivity of the technique are discussed.

Results of solar observations in the XUV-region by means of the telescope TEREK aboard the “Phobos-1” spacecraft are presented. Images of the Sun in the HeII 30,4 nm and FeIX-FeXI 17–18 nm lines were obtained with new types of optical elements — multilayer normal incidence XUV-mirrors and CCD-detectors. About 140 images were obtained with an angular resolution up to 15″ and with exposure times 0.1 to 40 s. In the images one sees the structures in the transition layer from corona to chromosphere which has temperatures in the range 5×104 – 1×106 K as well as in the polar and equatorial coronal holes. Besides, a unique phenomenon — a “blob” in outer corona at a distance about 2 solar radii has been observed. Processing of the data revealed a complex correlation between the XUV-images and the magnetic field structure in the photosphere.

Spectra of 3 large flares on 24 Oct., 5 Nov. and 16 Nov. 1970 in the region ? = 1.75–1.95 Å, obtained with the help of the ‘Intercosmos-4’ satellite during solar activity maximum are given. The physical conditions at the initial and final (decaying) phases are mainly studied. The line spectra are compared with hard continuum in the region 8–80 keV and results of polarization measurements, obtained simultaneously aboard the same satellite.