M. I. Kudryavtsev

The properties of gamma-radiation and high-energy neutron fluxes in "MIR" station orbit.

The study of radiation background components in the near-Earth space is very important for different branches of space research, in particular for space dosimetry and for the planning of gamma-astronomy experiments. Detailed information on the neutral components (gamma-quanta, neutrons) of background radiation was obtained during the Grif-1 experiment onboard Mir orbital station (OS). The measurements of fluxes of 0.05-50 MeV gamma-quanta and >30 MeV neutrons with a large area instrument (approximately 250 cm2 for gamma-quanta, approximately 30 cm2 for neutrons) as well as corresponding charged particle measurements (0.4-1.5 MeV electrons, 1-200 MeV protons) were made during this experiment. The background components induced by the stations own radiation as well as the albedo gamma-rays from the Earths atmosphere were revealed as the result of data analysis for about 600 h of observation. A mathematical model describing the latitude and energy dependences of atmospheric albedo gamma-rays as well as of those of gamma-quanta produced in the material of the station due to cosmic ray interactions was developed. An analytical approximation of the spectrum of induced gamma-rays from radioactive isotopes stored in the station and instruments materials is presented. The dynamics of gamma-quantum background fluxes during the geomagnetic disturbances of January 10-11, 1997 are discussed. An analytical representation of the latitude dependence of the integral flux of neutrons with >30 MeV is given.

Observations of soft gamma-ray or hard X-ray bursts in the GRIF experiment on the Mir orbiting station

During the GRIF experiment onboard the Mir orbiting station, the sky was monitored with a PX-2 wide-field (∼1 sr) scintillation X-ray spectrometer to detect bursts in the photon energy range 10–300 keV. Because of the comprehensive instrumentation, which, apart from the X-ray and gamma-ray instruments, also included charged-particle detectors, the imitations of astrophysical bursts by magnetospheric electron precipitations and strongly ionizing nuclei were effectively filtered out. It was also possible to separate solar and atmospheric events. Several tens of bursts interpreted as being astrophysical were detected in the experiment at sensitivity levels S∼10−7 erg cm−2 (for bursts whose spectra were characterized by effective temperatures kT∼100 keV) and S∼3×10−8 erg cm−2 (for bursts with kT∼25 keV). Some of the soft gamma-ray or hard X-ray bursts with kT∼10–50 keV were identified with the bursting pulsar GRO J1744-28. Our estimate of the detection rate for cosmological soft gamma-ray or hard X-ray bursts from the entire sky suggests that the distributions of long-duration (>1 s) gamma-ray bursts (GRBs) in characteristic energy kT and duration are inconsistent with the steady-state cosmological model in which the evolution of burst sources is disregarded. Based on GRIF and BATSE/CGRO data, we conclude that most of the GRB sources originate at redshifts 1

Statistics of faint gamma-ray bursts from the GRIF experiment on the Mir orbiting station

During the GRIF experiment onboard the Mir orbiting station, cosmic gamma-ray bursts (GRBs) were observed in the photon energy range 10–300 keV. We developed a technique for selecting events, cosmic GRB candidates, based on output readings from the PX-2 scintillation spectrometer, the main astrophysical instrument. Six events interpreted as cosmic GRBs were identified at a threshold sensitivity level of ≥10−7 erg cm−2. The GRIF burst detection rate recalculated to all the sky is ∼103 yr−1 (fluence ≥10−7 erg cm−2). This rate matches the BATSE/CGRO estimate and significantly differs from the value predicted by the S−3/2 dependence, which holds for a spatially uniform source distribution. The GRB detection rate at low peak fluxes is compared with the results of analysis for BATSE/CGRO “nontriggered” events and with predictions of major cosmological models. We conclude that the PX-2 observational data on faint cosmic GRBs are consistent with predictions of models with the highest frequency of GRB occurrence at z ≥1.5–2.

Observations of the X-ray binaries 4U 1700-37 and GRO J1655-40 during the Grif experiment onboard the mir orbiting station

Various areas of the sky, including the Galactic-center region and the region with the X-ray binaries 4U 1700-37 and GRO J1655-40, were observed in the hard (10–300 keV) energy range during the Grif experiment onboard the Mir orbiting station. An epoch-folding analysis of the data has revealed periodicities with periods of 82 and 62 h, which are equal to the orbital periods of 4U 1700-37 and GRO J1655-40. Previously, these periodicities were observed during the Prognoz-9 X-ray experiment. Periodicities with periods in the range of days, 98 and 152 h, which were also observed during the Prognoz-9 experiment, were not revealed by the Grif data. We obtained upper limits on the intensities of these periodicities in various energy ranges. For the 62-h periodicity, we constructed an average 25–50-keV light curve and estimated the spectral flux density, which characterizes the intensity of the periodic component at different energies in different observing intervals during 1995–1997. The Prognoz-9 and Grif observations of GRO J1655-40 are compared with its CGRO, RXTE, and BeppoSax observations. The orbital periodicity is shown to manifest itself in the hard emission from the extremely bright X-ray transient GRO J1655-40, a likely black-hole candidate, even at the epochs between its X-ray outbursts.

Short increases of the fluxes of electrons with energies > 0.08 MeV at low-latitude (L < 2) regions of near-Earth space

We present the characteristics of short (duration less than 1 min) increases of the counting rate of electrons with energies >0.08 MeV observed in low-latitude (L < 2.0) regions of near-Earth space in the course of the GRIF experiment on the Spektr module of the Mir orbital station. The measurements were carried out using a set of instruments including X-ray and gamma-ray spectrometers, as well as detectors of electrons, protons, and nuclei with large and small geometrical factors, which allowed one to detect the fluxes of charged particles both in the region of the Earth’s radiation belts and in regions close to the geomagnetic equator. As a result of more than 1.5 years of observation, it is demonstrated that short increases in the intensity of electrons of subrelativistic energies are detected not only in the regions of the near-Earth space known as “precipitation zones” (1.7 < L < 2.5), but in high-latitude regions (up to the geomagnetic equator, L < 1.1) as well. Two types of increases of the electron counting rate are found: either fairly regular increases repeating on successive orbits or increases local in time. The latter type of increases can be caused by a short enhancement of electron flux on a given drift shell. The results of our measurements have shown that the duration of the detected increases in intensity can be rather short, as little as 20–30 s. Therefore, in the case of large amplitudes, such increases of the counting rate of electrons can imitate astrophysical events of the type of cosmic gamma-ray bursts in the detectors of hard X-ray and gamma radiation.

Hard X-ray and gamma-ray spectrometer of high resolution and sensitivity on board the international space station (ISS)

Abstract The project of a spectrometer of hard X ( X h -rays and gamma-rays (approximate energy range 0.05 – 50 MeV) was proposed to a competition of scientific instruments to be accommodated onboard the international space station ( ISS ). The objectives of this experiment are as follows: detailed study of astrophysical phenomena including cosmic gamma-ray bursts ( GRB ), lines in Galactic diffuse background, e + e − annihilation line from the Galactic Centre and high resolution observation of solar X h -rays and gamma-radiation in lines and continuum. The spectrometer detector system includes three enriched Ge crystals (each of ∼200 cm 3 volume) cooled to 4 cm 3 volume) with crossed axes. The effective instrument field of view is about π sr. The expected energy resolution at 1 MeV for Ge and NaI are ∼2 keV and ∼50 keV, respectively. The detection of solar flares neutrons is also possible by this instrument owing to the separation of different components of light flashes in CsI . The program of ISS provides a long exposure time for the detectors of the proposed spectrometer. Using results of the “ Grif-1 ” experiment onboard the “ Mir ” station we obtain that it will be possible to accomplish precise X h and gamma-measurements under background conditions onboard ISS .

The project of all-sky hard X-ray and soft gamma-ray monitoring on-board international space station

Further progress in hard X-ray and soft gamma-ray observations can be achieved in the experiments with wide-field code-aperture instruments, which allow, due to long exposure times, to achieve the timing of different astrophysical objects (possible even in the near-Earth missions). The deep all-sky survey at the level of registration ∼100 new sources (mainly Active Galactic Nuclei) in the energy range ∼0.3–1 MeV is possible in the observations made during ∼10 years with the instrument with ∼2π FOV, ∼1000–3000 cm2 effective area and ∼3°–5° angular resolution. The gamma-telescope “Gammascope” with such characteristics is now being elaborated. It is proposed for the experiment on the International Orbital Station “Alpha”. The instrument is based on a combination of the quasi-spherical coding-mask and NaICsI position-sensitive detector (PSD).

Temporal and spectral parameters of slow X-ray periodic sources observed during Prognoz 9 mission

Abstract Periodic components in hard X-rays from some objects near the Galactic Center were discovered in the experiment during Prognoz-9 mission. The corresponding period values lay in the range from several hours to several days. Some of these periodic processes were identified with the X-ray binaries which were not known before as eclipse systems: H1705-25 (Nov Oph 1977) - 152 h, Sco X-1 - 62 h, Cen X-4 -8.2 h, 4U1755-33 - 4.4 h. Other periods are still unidentified: 98 h, 69 h, 13 h, 9.4 h, 7.8 h, 3.4 h, 1.96 h. The common property of all these processes is the very complicated form of mean light curves similar to those pulse profiles which were obtained for ordinary “more fast” (with periods less than 1000 s) X-ray pulsars. The energy spectra of these sources are characterized by the values of the effective temperature kT in the range from ∼5 (1.96 h) to >40 keV (152 h).

X-ray timing in the astrophysical experiment on-board “Mir-Spectr” orbital complex

A multipurpose experiment with a number of instruments is being conducted on-board the “Mir-Spectr” orbital complex. Observations began on October 5, 1995. The main astrophysical instrument is a wide-field oriented scintillator spectrometer (∼300 cm2 effective area, 10–300 keV energy range). It consists of 7 identical detector units with the axes turned 5° to each other, which allows us to determine the direction on the source of the registered photons. The significant peculiarity of the experiment is the possibility of the continuous monitoring of gamma-quanta and relativistic electrons fluxes, which are responsible for those background components in the X-ray spectrometer, which can not be removed by instrumental methods. Due to the long exposure time and accurate background patrol, the X-ray timing of different galactic sources (including Sco X-1, Cyg X-1, Crab) as well as the registration of hard X-ray bursts (especially from the Soft Gamma-ray Repeaters) and transients are quite realistic in the experiment (the fluxes of weakest detectable bursts from SGR is ≤10−8 erg/cm2).

GRIF-1 experiment on board the SPEKTR/MIR orbital complex: Study of solar X-ray, gamma-ray, and neutron flares and correlation of magnetosphere-charged particle fluxes with solar activity

The SPEKTR module of the MIR orbital station was launched in May 1995. The multipurpose experiment was based on the GRIF-1 research complex consisting of an oriented X-ray spectrometer, a spectrometer of gamma-quanta and neutrons, a spectrometer of electrons and protons with a large geometrical factor, and a spectrometer of electrons, protons, and nuclei with a small geometrical factor. The solar geophysical aspects of the experiment included the measurements of spectral and temporal parameters of solar hard electromagnetic (0.01–50 MeV) and neutron (>20 MзB) radiation, the study of spectral, temporal, and spatial characteristics of energetic electrons (0.04–1.5 MeV), protons, and nuclei (1–200 MeV/nucleon) in the circumterrestrial space, as well as the correlations of these parameters with solar activity phenomena.