Yu. V. Ozerov

Eye light flashes on the mir space station

The phenomenon of light flashes (LF) in eyes for people in space has been investigated onboard Mir. Data on particles hitting the eye have been collected with the SilEye detectors, and correlated with human observations. It is found that a nucleus in the radiation environment of Mir has roughly a 1% probability to cause an LF, whereas the proton probability is almost three orders of magnitude less. As a function of LET, the LF probability increases above 10 keV/micrometer, reaching about 5% at around 50 keV/micrometer.

Study of cosmic rays and light flashes on board Space Station MIR: The SilEye experiment

The SilEye experiment aims to study the cause and processes related to the anomalous Light Flashes (LF) perceived by astronauts in orbit and their relation with Cosmic Rays. These observations will be also useful in the study of the long duration manned space flight environment. Two PC-driven silicon detector telescopes have been built and placed aboard Space Station MIR. SilEye-1 was launched in 1995 and provided particles track and LF information; the data gathered indicate a linear dependence of FLF(Hz) ( 4 2) 10(3) 5.3 1.7 10(4) Fpart(Hz) if South Atlantic Anomaly fluxes are not included. Even though higher statistic is required, this is an indication that heavy ion interactions with the eye are the main LF cause. To improve quality and quantity of measurements, a second apparatus, SilEye-2, was placed on MIR in 1997, and started work from August 1998. This instrument provides energetic information, which allows nuclear identification in selected energy ranges; we present preliminary measurements of the radiation field inside MIR performed with SilEye-2 detector in June 1998.

Study of the radiation environment on MIR space station with SILEYE-2 experiment.

In this work we present preliminary results of nuclear composition measurements on board space station MIR obtained with SILEYE-2 particle telescope. SILEYE-2 was placed on MIR in 1997 and has been working since then. It consists of an array of 6 active silicon strip detectors which allow nuclear and energetic identification of cosmic rays in the energy range between approximately 30 and 200 MeV/n. The device is attached to an helmet and connected to an eye mask which shields the cosmonaut eyes from light and allow studies of the Light Flashes (LF) phenomenon. In addition to the study of the causes of LF, the device is used to perform real time long term radiation environment monitoring inside the MIR, performing measurements in solar quiet and active days.

A wide aperture telescope for high energy gamma rays detection

In this paper new techniques for the realization of a high energy gamma-ray telescope are presented, based on the adoption of silicon strip detectors and lead scintillating fibers. The simulated performances of this instrument show that the silicon strip technology adopted by GILDA (Gamma-ray Imaging Large Detector for Astrophysics) could improve the performance of EGRET, which is so far the most successful experiment of a high energy gamma-ray telescope, though having less volume and weight.

Repeated gamma-ray bursts from the June 15, 1991 solar flare

The results of the detection of repeated bursts of gamma rays with energies exceeding 30 MeV from the June 15, 1991 solar flare, observed with the Gamma-1 telescope, are examined. It is shown that they occur on the declining part of the temporal profile of the gamma radiation and last for ∼10 min (they occur 27 min after the optical part of the flare starts). No appreciable radiation bursts were observed during the subsequent quasiconstant part (∼20 min). It is concluded that repeated events in which particles are accelerated occur in the active stage of the powerful June 15, 1991 solar flare. It is noted that while the June 15, 1991 and March 26, 1991 gamma-ray bursts share a common character, their spectral and temporal characteristics are substantially different.

Energy spectra of solar flare gamma-ray emission in the range 0.03–2 GeV registered by gamma-1 telescope

Abstract The gamma-ray telescope GAMMA-1 has registered gamma-emission in the range 30 – 2000 MeV from two solar flares. Spectral analysis with the use of maximum likelihood and maximum entropy methods has revealed the difference of gamma-ray production mechanism. In contrast with impulsive March 26, 1991 event where high energy gamma-rays originate exclusively as a bremstrahlung of primary accelerated electrons, at the extended phase of June 15, 1991 flare mainly the decay of neutral pions is responsible for the observed gamma-emission. An average spectral index for primary nucleons was -3.6. Evolution of the spectra for both flares shows tendency to a decrease of the primary particles mean energies with time.

Geminga pulsar observations with gamma-telescope Gamma-1

Abstract The Geminga light curve obtained with the “Gamma-1” telescope features two peaks separated by 0.5 ± 0.03 period. The light curve is pronounced for γ-quanta energies higher than 400 MeV. The pulsed flux upper limit (1σ) in the energy interval 50 – 300 MeV is 6·10 −7 cm −2 sec −1 . For energies >300 MeV the pulsed component power law spectrum has an exponent 1.1 −0.3 +1.1 and an integral flux (1.1±0.3)·10 −6 cm −2 sec −1 .

Determining the Characteristics of Cosmic-Radiation Nuclei in the Sileye Experiment on Board the Mir Orbital Station

An algorithm for reconstructing the characteristics (charge, mass, and energy) of cosmic-radiation nuclei with 20- to 200-MeV/nucleon energies is described. The detector is a telescope of three two-coordinate planes with two 1-mm-thick iron filters inserted between them. Each plane is composed of two strip silicon detectors with 3.6-mm-wide orthogonally oriented strips, an effective area of 6 × 6 cm2, and a thickness of 380 μm. The algorithm for reconstructing the nuclei characteristics is based on the analysis of how the specific ionization losses change as the nuclei pass through the filter material. The results of the Monte Carlo simulation are presented for the energy dependence of the telescope acceptance and the energy deposited in the detectors by different nuclei in view of the detector calibration on the nuclear beams of the accelerator. The mass resolution of the telescope is ∼30, 12, and 5% for He, N, and Al nuclei, respectively. The energy resolution, which is ∼20%, is much the same for all nuclei.

Time variations of high energy gamma emission of Vela Pulsar observed by GAMMA-1 telescope

Abstract Two observations of the Vela Pulsar in the energy range 50–5000 MeV performed with the GAMMA-1 telescope in 1990 and 1991 allowed us to study time variability of the pulsar light curve and energy spectra. The light curve for Eγ > 50 MeV shows definite variations in the first interpeak phase interval. The energy spectra of the two main peaks and first interpeak in the lightcurve vary significantly below 200 MeV.

Determination of the characteristics of the gamma-ray telescope Gamma-1

The ‘Gamma-1’ telescope has been developed through a collaboration of scientists in the USSR and France in order to conduct γ-ray astronomical observations within the energy range from 50 to 5000 MeV. The major characteristics of the telescope were established by Monte-Carlo simulations and calibrations made with the aid of electron and ‘tagged’ γ-ray beams produced by an accelerator, and these have been found to be as follows: the effective area for photons coming along the instruments axis varies from about 50 cm2 at Eγ = 50 MeV to approximately 230 cm2 at Eγ ≥ 300 MeV; the angular resolution (half opening of the cone embracing 68% events) is equal to 2.7° at Eγ = 100 MeV, and 1.8° at Eγ = 300 MeV; the energy resolution (FWHM) varies from 70% to 35% as the energy of the detected photons increases from 100 to 550 MeV; the telescopes field-of-view at the half-sensitivity level is 300–450 square degrees depending upon the spectrum of the detected radiation, and the event selection logic. Proceeding from the thus obtained characteristics it is demonstrated that a point source producing a photon flux J (Eγ ≥ 100 MeV) = 3 × 10-7 cm-2 s-1, can be detected with a 5σ significance by observing it during 106 s at the level of the Cygnus background, and a source having intensity J (Eγ ≥ 100 MeV) = 10-6 cm-2 s-1 can be detected to within a mean square positional accuracy of about 15′.