V. N. Yurov

RT-2 DETECTION OF QUASI-PERIODIC PULSATIONS IN THE 2009 JULY 5 SOLAR HARD X-RAY FLARE

We present the results of an analysis of hard X-ray observations of the C2.7 solar flare detected by the RT-2 experiment on board the Coronas-Photon satellite. We detect hard X-ray pulsations at periods of {approx}12 s and {approx}15 s. We find a marginal evidence for a decrease in period with time. We have augmented these results using the publicly available data from the RHESSI satellite. We present a spectral analysis and measure the spectral parameters.

High-sensitivity STEP-F spectrometer-telescope for high-energy particles of the CORONAS-PHOTON satellite experiment

The STEP-F satellite telescope for measuring electrons and protons of the Photon scientific equipment is described. Its design features are given. The device detects electrons, protons, and α-particles in the energy range 0.18–2.3, 7.4–55.2, and 298–160.0 MeV, respectively. Geometric factors vary in the range of 12.4–21.7 cm2 sr, depending on the energy of the particles. In addition, there are three channels of mixed recording of particles of different types and channels of recording of the secondary electromagnetic radiation generated in the construction materials of the device and spacecraft. Methods and results of the computer simulation of the passage of the particle through detector materials are presented, along with configuration, calibration measurements, and tests (both standalone and integrated) within the complex of scientific instrumentation and spacecraft. Updated data on geometric factors of the device and energy ranges of the direct detection of charged high-energy particles and of channels of mixed recording of several types of particles are given. Special software is described for the rapid analysis of the processed data of the STEP-F telescope, and the visualization of time variations of particle fluxes with different time resolution in some periods of high solar activity and in its absence.

Experimental study of parameters of X-ray radiation from solar flares using the PENGUIN-M instrument aboard the CORONAS-PHOTON spacecraft

The main characteristics of the PENGUIN-M instrument are given. The instrument has been operating aboard the CORONAS-PHOTON spacecraft (SC) launched into orbit on January 30, 2009. The instrument includes the PENGUIN-MD detector unit (PMD) and the PENGUIN-ME electronic unit (PMD). The purpose of the experiment is to measure the degree of linear polarization of X-ray radiation from solar flares in the energy range of 20–150 keV and to obtain energy spectra of X-ray radiation from solar flares in the energy range of 2–500 keV. The paper describes the instrument, calibration procedure, and in-flight adjustment, and contains the first results of measurements.

PHOKA experiment: Description of the equipment and first results

The CORONAS-PHOTON Russian satellite intended to study the Sun was successfully launched into orbit on January 30, 2009. Scientific equipment of the satellite includes the PHOKA radiometer of soft X-ray and extreme UV radiation. The PHOKA instrument is intended to measure the absolute flux of solar electromagnetic radiation in the spectral windows of 0.5–7 nm, 0.5–11 nm, 27–37 nm, and 116–125 nm. When leaving and entering the Earth’s shadow, the instrument aboard the spacecraft measures absorption of radiation by various layers of the Earth’s atmosphere. Before the launch, photodiodes of the instrument had been calibrated using a synchrotron radiation source. In-flight stability of sensitivity of main channels is controlled using calibration channels. The paper describes the PHOKA instrument and presents its capabilities and main characteristics, as well as some results of its operation in orbit.

The NATALYA-2M spectrometer of high-energy radiations for the CORONAS-PHOTON space project

The NATALYA-2M high-energy radiation spectrometer is an element of the complex of scientific equipment of the CORONAS-PHOTON satellite. The instrument intended for registering gamma radiation of solar flares in the broad energy range of 0.2–1600 MeV as well as neutrons of solar origin with energies of 20–300 MeV represents itself as a scintillation spectrometer based on CsI(Tl) crystals with a total area of 32 × 38 cm2 and the thickness of 18 cm. The spectra and time profiles of the gamma quanta count rates are measured in four subranges: R (0.2–2 MeV), L (1–18 MeV), M (7–250 MeV), and H (50–1600 MeV). Depending on the gamma radiation energy, the effective area of the instrument varies within the range from 750 to 900 cm2, and the energy resolution at the Cs-137 line (662 keV) is 10%, it being about 30% at energies higher than 50 MeV. A system of stabilization based on the signal from the generator of reference light pulses is used to provide stability and automated adjustment of the parameters of spectrometric modules. The measuring channels of the instrument are calibrated during the flight using a source of “tagged” gamma quanta on the Co-60 radioactive isotope. Polystyrene scintillation counters are used to provide protection from the background of charged particles. The “CORONAS-PHOTON” spacecraft (SC) was launched from the Plesetsk spaceport on January 30, 2009, to a low circular near-Earth orbit (the altitude is 550 km, the inclination is 82.5°). On February 27, the first scientific data were obtained from the NATALYA-2M instrument. The results of the flight calibration of the instrument detectors in different energy channels demonstrated good agreement with the ground measurements. The paper describes the instrument and observational potentials of the NATALYA-2M spectrometer, gives the results of the adjustment and calibration, and exemplifies the registration of gamma-ray bursts (GRBs)on the orbit.

Linearity of the energy scale of a detector based on a LaBr3(Ce) scintillator

The linearity of a LaBr3(Ce) detector response in the energy range of 0.6–11.0 MeV has been investigated using various PMT voltage divider circuits. A tapered voltage divider circuit is proposed to reduce the nonlinearity.

The experiment with the fast X-ray monitor (BRM) instrument onboard the CORONAS-PHOTON satellite

The “Fast X-ray Monitor” (BRM) instrument operated in the complex of the scientific instruments onboard the CORONAS-PHOTON satellite from February 19, 2009, until December 1, 2009. The instrument is intended for the registration of the hard X-ray radiation of solar flares in the 20–600 keV energy range in six differential energy channels (20–30, 30–40, 40–50, 50–70, 70–130, and 130–600 keV) with temporal resolution to 1 ms. In the instrument, a detector based on the YAP: Ce scintillator is used; this detector is 70 mm in diameter and 10 mm thick (the decay time is about 28 ns). For the decrease of the back-ground charge of the detector, the collimator limiting the angle of view of the instrument of value 12° is mounted over the scintillator. The effective area of the detector amounts to 27.7 cm2 (at the X-ray radiation energy 80 keV), and the dead time of the detector is 1 μs. Over the operation onboard the CORONAS-PHOTON satellite, the BRM instrument has registered gamma ray burst series and, perhaps, one solar flare of the class C1.3 on October 26, 2009.

EUV-Phoka — Multi-channel monitor for measurements of transmittance of solar EUV-emission in the thermosphere

Abstract EUV-Phoka is intended to record solar soft X-ray and EUV radiation (1 – 130 nm) in six spectral windows. Each channel includes a silicon photodiode AXUV-100 with a collimator and an appropriate spectral filter, a preamplifier and a voltage-to-frequency converter. The precession of the measurement by the diode is better than 1%, and the absolute accuracy is about 10 %. — In addition, there is a channel to record the visual light. EUV-Phoka will be installed onboard the “PHOTON” satellite, which is oriented to the Sun. Occultation measurements will provide a data base to derive parameters such as neutral temperature and density profiles for theoretical and empirical modeling of the thermosphere and ionosphere in the altitude range from 100 to 450 km. N o Spectral window Main emissions Solar origin 1 Corona 2 17 – 35 nm 30.4 nm - HeII Transition region 3 55–63 nm 58.4 nm - HeI Chromosphere 4 70 – 90 nm 80 nm - OII - OIV Transition region 5 90 – 110 nm 102.6 nm - Ly-β Chromosphere 6 120 – 130 nm 121.6 nm - Ly-α Chromosphere 7 400 – 1100 nm Photosphere During the last years many space experiments such as the YOHKOH, CORONAS-1 and SOHO missions collected solar XUV/EUV data with high spatial and spectral resolutions whereas the primary goal of EUV-Phoka is defined to determine the spectral irradiance from the total solar disk within the broadest wavelength range by the group of PHOTON experiments [1,2].

Performances investigation and material selection of PMT magnetic shields for the space experiments with GRIS and PING-M instruments

PMT performances significantly change under the influence of magnetic field. Even the relatively weak geomagnetic field, which typically value is about 0.5 gauss, has an appreciable effect. Gain variations of PMT with 76 mm photocathode diameter may reach 10-20% depending on spatial orientation. Therefore, it is necessary to apply magnetic shields for PMT response stability enhancement. The performances investigation of magnetic shields made of steel, permalloy and amorphous metallic alloy ribbon for PMT with 51 and 76 mm photocathode diameters was carried out. Based on obtained data the choice of magnetic shield was made.

The Study of the Cosmic Gamma-Emission Nonstationary Fluxes Characteristics by the AVS-F Apparatus Data

The AVS-F apparatus (Russian abbreviation for Amplitude-Time Spectrometry of the Sun) is intended for the solar flares’ hard X-ray and gamma-ray emission characteristic studies and for the search and detection of the gamma-ray bursts (GRB). At present over 1,100 events with duration more than 2 s without any coordinate relations to Earth Radiation Belts and South Atlantic Anomaly were separated on the results of preliminary analysis of AVS-F experiment database.About 68 % of the identified events were associated with quasistationary equatorial precipitations-15-30 % count rate increases in the low-energy gamma-band of the AVS-F apparatus over its average value obtained by approximation of these parts with polynomials discovered on some equatorial segments in the ranges of geographic latitude of 25∘ up to +30∘. Several short events with duration of 1-16 ms associated with terrestrial gamma-ray flashes were registered during the experiment. These events were detected above the powerful thunderstorm formations.Solar flares with classes stronger than M1.0 according to the GOES classification were about 7 % of the detected events. Solar flares’ hard X-rays and γ-emission were mainly observed during the rise or maximum phases of the emission in the soft X-rays band according to the detectors on board the GOES series satellites data and duration of their registration is less than of the soft X-ray bands. According to the preliminary data analysis gamma-emission with energy over 10 MeV was registered during 12 % of the observed flares. The emission in the energy band E ? 100 keV was registered during over 60 faint solar flares (of B and C classes according to the GOES and from several ones γ-quanta with energy up to several tens of MeV were observed.Several spectral line complexes were observed in the spectra of some solar flares stronger than M1.0 in the low-energy gamma-range. Registered spectral features were corresponded to α α-lines, annihilation line, nuclear lines, and neutron capture line on1H (2.223 MeV). In the spectrum of the January 20, 2005 solar flare the feature in the range of 15-21 MeV was detected for the first time. It can be associated with lines of 15.11 MeV (12C +16O) or 20.58 MeV (from neutron radiative capture on3He), or with their combination. Also several e-dominant flares without any gamma-lines in energy spectra were identified. All detected faint solar flares were e-dominant according to the preliminary data analysis.Thin structure with characteristic timescale of 30-160 s was observed at 99 % significance level on some solar flares stronger than M1.0 temporal profiles in the low-energy gamma-band in the energy ranges corresponding to the identified spectral features or whole gamma-band energy boundaries. According to the results of the preliminary analysis during the flare of January 20, 2005, thin structure with timescale from 7 ms to 35 ms was detected at 99 % confidence level in the energy range of 0.1-20 MeV. Some thin structure with characteristic timescale 50-110 s was observed on temporal profiles of several faint events.About 3 % of the identified events were gamma-ray bursts. During some bursts high-energy gamma-emission was observed, for example Emax = 147 ± 3 MeV for GRB050525.