Context. The 2003 October 28 (X17.2) eruptive flare was a unique event. The coronal electric field and the pi-decay gamma-ray emission flux displayed the highest values ever inferred for solar flares. Aims. Our aim is to reveal physical links between the magnetic reconnection process, energy release, and acceleration of electrons and ions to high energies in the chain of the magnetic energy transformations in the impulsive phase of the solar flare. Methods. The global reconnection rate, phi(t) phi and the local reconnection rate (coronal electric field strength), E-c(r, t), were calculated from flare ribbon separation in H alpha filtergrams and photospheric magnetic field maps. Then, HXRs measured by CORONAS-F/SPR-N and the derivative of the GOES SXR flux, & Idot;(SXR)(t) were used as proxies of the flare energy release evolution. The flare early rise phase, main raise phase, and main energy release phase were defined based on temporal profiles of the above proxies. The available results of INTEGRAL and CORONAS-F/SONG observations were combined with Konus-Wind data to quantify the time behavior of electron and proton acceleration. Prompt gamma-ray lines and delayed 2.2 MeV line temporal profiles observed with Konus-Wind and INTEGRAL/SPI were used to detect and quantify the nuclei with energies of 10-70 MeV. Results. The magnetic-reconnection rates, phi(t) and E-c(r, t), follow a common evolutionary pattern with the proxies of the flare energy released into high-energy electrons. The global and local reconnection rates reach their peaks at the end of the main rise phase of the flare. The spectral analysis of the high-energy gamma-ray emission revealed a close association between the acceleration process efficiency and the reconnection rates. High-energy bremsstrahlung continuum and narrow gamma-ray lines were observed in the main rise phase when E-c(r, t) of the positive (negative) polarity reached values of similar to 120 V cm(-1) (similar to 80 V cm(-1)). In the main energy release phase, the upper energy of the bremsstrahlung spectrum was significantly reduced and the pion-decay gamma-ray emission appeared abruptly. We discuss the reasons why the change of the acceleration regime occurred along with the large-scale magnetic field restructuration of this flare. Conclusions. The similarities between the proxies of the flare energy release with phi(t) and E-c(r, t) in the flare's main rise phase are in accordance with the reconnection models. We argue that the main energy release and proton acceleration up to subrelativistic energies began just when the reconnection rate was going through the maximum, that is, following a major change of the flare topology.

We analyze here the impulsive phase of the 2001 August 25 eruptive flare (X5.3, S21, E38) in order to reveal the link of the time evolution of the magnetic-field reconnection rate φ̇(t) with the energy-release process, as quantified by electron and proton acceleration to high energies. Hard X-rays and -rays from 150 keV to 100 MeV were observed by the SONG (SOlar Neutrons and Gamma) detector onboard the CORONAS-F (Complex ORbital ObservatioNs of the Active Sun) mission. The soft X-ray derivative dI_SXR/dt was used as a proxy for the flare energy release that revealed itself as a sequence of acceleration pulses. The reconnection rate φ̇(t) was calculated previously from flare-ribbon observations in EUV and coaligned magnetic-field maps. The -ray emission spectra were obtained from SONG data. All spectra contain both bremsstrahlung and -ray lines. The bremsstrahlung spectrum extends to tens of MeV. The pion-decay gamma-ray emission, being a manifestation of proton acceleration to subrelativistic energies, appeared for the first time in the time interval of the φ̇(t) maximum. This maximum was ahead of the maxima of dI_SXR/dt as well as of all other emissions by about one minute. Proton acceleration to subrelativistic energies is confirmed by detection of solar neutrons by SONG and the Chacaltaya neutron monitor.

Appreciable hard X-ray (HXR) and gamma-ray emissions in the 0.04 to 150 MeV energy range associated with the 2003 October 29 solar flare (X10/3B) were observed at 20:38 to 20:58 UT by the SONG instrument onboard the CORONAS-F mission. To restore flare gamma-ray spectra we fitted the SONG energy loss spectra with a three-component model of the incident spectrum: (1) a power law in energy, assumed to be due to electron bremsstrahlung; (2) a broad continuum produced by prompt nuclear de-excitation gamma-lines; and (3) a broad gamma-line generated from pion decay. We also restored spectra from the RHESSI data, compared them with the SONG spectra and found a reasonable agreement between these spectra in the 0.1 to 10 MeV energy range. The pion-decay emission was observed from 20:44:20 UT and had its maximum at 20:48 to 20:51 UT. The power-law spectral index of accelerated protons estimated from the ratio between intensities of different components of gamma rays changed with time. The hardest spectrum with a power-law index S = - 3.5 to - 3.6 was observed at 20:48 to 20:51 UT. Time histories of the pion-decay emission and proton spectrum were compared with changes of the locations of flare energy release as shown by RHESSI hard X-ray images and remote H alpha brightening. An apparent temporal correlation between processes of particle acceleration and restructuring of flare magnetic field was found. In particular, the protons were accelerated to sub-relativistic energies after radical change of the character of footpoint motion from a converging motion to a separation motion.

July 1, 2016 was the 100th anniversary of the birthday of the eminent Russian astrophysicist Iosif Samuilovich Shklovskii (1916–1985), who was a corresponding member of the USSR Academy of Sciences, a recipient of the Lenin Prize, and a member of the National Academy of Sciences of the USA, the Royal Astronomical Society, and many other academies. Iosif Samuilovich made important and fundamental contributions in many areas of modern astrophysics, and is the author of nine books and more than 300 scientific publications. The Russian Academy of Science, Astro Space Center of the Lebedev Physical Institute, Space Research Institute of the Russian Academy of Sciences, the Sternberg Astronomical Institute of Moscow State University, and the Astronomical Society held the international conference “All-Wave Astronomy. Shklovskii-100” to commemorate this anniversary. This issue of Astronomy Reports presents papers based on selected talks at this conference.

HXR and gamma-ray emissions in the 0.04-150 MeV energy range associated with the solar flare on 29 October 2003 (X10/3B) were observed at 20:38-20:58 UT by the SONG instrument aboard the CORONAS-F mission. We restored consecutive flare gamma-emission spectra from SONG and RHESSI data and found a good agreement of these spectra in the 0.1-10 MeV energy range. Two phases were identified which showed major changes in the spectral shape of flare emission: 20:38:00-20:44:20 UT and 20:44:20-20:58:00 UT. During the second phase an efficiency of proton acceleration increased considerably relatively to the efficiency of acceleration of high energy electrons. The pion-decay component of the flare gamma-emission was elicited statistically significant only during the second phase since 20:47:40 UT. A power law spectrum index of accelerated protons was estimated from the ratio between intensities of the pion-decay and gamma-line components. The hardest spectrum (power law index S=3.7) was at 20:48-20:51 UT when the intensity of the pion-decay emission was maximal. Our subdivision of the flare into two phases is consistent with sharp changes in the structure of the flare found by Ji et al. (2008) and Liu et al. (2009).This flare was accompanied by GLE 66. The time profile of the pion-decay gamma-emission was compared with the GLE onset time. It was shown that both protons interacting at the Sun and the particles responsible for the GLE onset could belong to the same population of accelerated particles.

Virtually all physical processes occurring during hydrogen and helium recombination (900 < z < 7000) are currently well understood. The theoretical work of the last decade on this topic provides a comprehensive picture of recombination and related processes. Of particular observational interest is the fact that the CMB spectrum experiences a unique distortion from the blackbody spectrum due to the release of photons during this epoch. These additional photons form a cosmological recombination spectrum imposed on the thermal CMB spectrum. The recombination dynamics of hydrogen are controlled by two processes the two-photon decay 2s -> 1s and the La photon escape due to multiple scattering in an expanding medium of which the first is dominant. About 57% of all hydrogen atoms in the Universe at z less than or similar to 1400 recombined through the two-photon decay channel. Because the ratio of the CMB photon and baryon number densities is extremely large, the additional photons make up only a small fraction (10(-8)-10(-9)) of the total number, and hence their distorting effect of the CMB spectrum is small. Of most promise for future observations are relative distortions in the Rayleigh-Jeans range of the CMB spectrum (the decimeter range). For example, at 300 MHz, relative intensity distortions of the order of 10(-8)-10(-9) are expected. The Balmer and Paschen hydrogen series fall into the range of a CMB maximum. In the Wien range, observations are greatly hampered and indeed made impossible by the infrared and submillimeter cosmic background. Given the current level of instrumentation, it is not yet possible to measure small distortions (< 10(-8)) near the maximum. Some researchers believe, however, that an accuracy of similar to 10 nK can soon be achieved. Because the CMB spectrum does not depend on the direction, any region of the sky can be chosen for observation, preferably so as to minimize the contribution of various cosmic backgrounds and noises (for example, near a galactic pole). It is also essential that the sought signal be nonpolarized in order that it can be separated from signals from other sources.

The question of the Sun's motion relative to the local interstellar medium (LISM) is examined. Results from Russian, US, and French satellites and space probes observing scattered solar radiation in hydrogen Lyman-alpha (lambda = 1215.7 angstrom) and helium (lambda = 584 angstrom) lines are presented. Data are briefly discussed on the direct registration inside the Solar System of neutral helium atoms, picked-up helium ions, and fast neutral hydrogen atoms entering from the LISM. The fast neutral hydrogen atoms arise in the region of solar wind-LISM interaction.

The aim of this work is to determine the instant of acceleration at the Sun of protons responsible for the onset of the ground-level enhancements (GLEs). Using a set of data on peak soft X-ray intensity derivatives and hard X-ray and gamma radiation intensities along with radio burst intensities in the cm/mm range, we the time interval of the maximum solar energy release for flares associated with 45 GLEs (27 through 71). We also determined the times of GLE onset for the same events. In 31 events, the time of GLE onset lagged 2–15 minutes behind the observed maximum of flare energy release. Such brief lags suggest that the effective acceleration of the protons responsible at least for the onset of GLEs occurs typically within the time interval of maximum flare energy release.

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We analyze experimental data on the temporal behavior of fluxes and energy spectra of hard solar X-ray and gamma radiation in the energy range of 0.015 to 300 MeV, obtained onboard the CORONAS-F satellite during a solar flare on August 25, 2001. These data are compared with measurements of the radio emission fluxes over the wide frequency range of 1–405 GHz. For our analysis, we use data obtained onboard the YOHKOH, TRACE and GOES satellites, along with ground-based observations of this solar event using the Solar Submillimeter Telescope (SST; Argentina). For the first time, we find nearly simultaneous changes in the energy spectra of gamma radiation over the range 10–150 MeV and the frequency spectrum of radio emission at the beginning and during a impulsive phase of this event (whose duration did not exceed three minutes).

The catalog of ground level enhancements of solar cosmic rays during cycles 21-23 of solar activity has been presented. The main properties, time distribution, and relation of these events to solar sources and proton enhancements observed on satellites have been studied.

We consider the problem of optical detection of hazardous asteroids of 100–1000 m diameter on the Earth’s surface and in space. Appropriate instruments suitable for solving this problem are also considered.

We present a multi-frequency and multi-instrument study of the 20 January 2005 event. We focus mainly on the complex radio signatures and their association with the active phenomena taking place: flares, CMEs, particle acceleration, and magnetic restructuring. As a variety of energetic-particle accelerators and sources of radio bursts are present, in the flare – ejecta combination, we investigate their relative importance in the progress of this event. The dynamic spectra of ARTEMIS-IV – Wind/Waves – HiRAS, with 2000 MHz – 20 kHz frequency coverage, were used to track the evolution of the event from the low corona to the interplanetary space; these were supplemented with SXR, HXR, and γ-ray recordings. The observations were compared with the expected radio signatures and energetic-particle populations envisaged by the Standard Flare – CME model and the reconnection outflow termination shock model. A proper combination of these mechanisms seems to provide an adequate model for the interpretation of the observational data.