Alex Zehnder

The Reflection Grating Spectrometer on board XMM-Newton

The ESA X-ray Multi Mirror mission, XMM-Newton, carries two identical Reflection Grating Spectrometers (RGS) behind two of its three nested sets of Wolter I type mirrors. The instrument allows high- resolution (E=E = 100 to 500) measurements in the soft X-ray range (6 to 38 A or 2.1 to 0.3 keV) with a maximum eective area of about 140 cm 2 at 15 A. Its design is optimized for the detection of the K-shell tran- sitions of carbon, nitrogen, oxygen, neon, magnesium, and silicon, as well as the L shell transitions of iron. The present paper gives a full description of the design of the RGS and its operational modes. We also review details of the calibrations and in-orbit performance including the line spread function, the wavelength calibration, the eective area, and the instrumental background.

X-Ray Polarization of Solar Flares Measured with Rhessi

The degree of linear polarization in solar flares has not yet been precisely determined despite multiple attempts to measure it with different missions. The high energy range, in particular, has very rarely been explored, due to its greater instrumental difficulties. We approached the subject using the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) satellite to study six X-class and 1 M-class flares in the energy range between 100 and 350 keV. Using RHESSI as a polarimeter requires the application of strict cuts to the event list in order to extract those photons that are Compton scattered between two detectors. Our measurements show polarization values between 2 and 54%, with errors ranging from 10 to 26% in 1σ level. In view of the large uncertainties in both the magnitude and direction of the polarization vector, the results can only reject source models with extreme properties.

The ESA Standard Radiation Environment Monitor program first results from PROBA-I and INTEGRAL

The main characteristics of the European Space Agency (ESA) Standard Radiation Environment Monitor (SREM) are outlined. First SREM results from the Project for On-Board Autonomy-I (PROBA-I) and INTEGRAL spacecraft are presented.

The Proton Irradiation Facility at the Paul Scherrer Institute

Abstract Under a European Space Agency contract the Proton Irradiation Facility has been designed and constructed in the new Paul Scherrer Institute Nucleon Area primarily for terrestrial proton testing of components and materials for spacecraft. Emphasis has been given to generating realistic proton spectra encountered by space-flights at any potential orbit. The Proton Irradiation Facility provides proton beam with energies from 30 to 300 MeV and dose rates up to ca. 11 rad s −1 per 10 μA (maximum 20 μA) proton current from a beam splitter. The maximum irradiation field is equal to 10 × 10 cm 2 . The facility, designed in a user friendly manner, can be readily adapted to the individual requirements of experimenters. Its principal features are: a transparent operating procedure, a fast and uncomplicated set-up, and a broad range of energies and intensities of the proton beam. The facility is available for general use and apart from components irradiations for space and material research it serves in testing particle detectors and radiation monitors as well as for proton experiments in different disciplines of natural science.

Radiation environment along the INTEGRAL ? orbit measured with the IREM monitor

The INTEGRAL Radiation Environment Monitor (IREM) is a payload supporting instrument on board the INTEGRAL satellite. The monitor continually measures electron and proton fluxes along the orbit and provides this information to the spacecraft on board data handler. The mission alert system broadcasts it to the payload instruments enabling them to react accordingly to the current radiation level. Additionally, the IREM conducts its autonomous research mapping the Earth radiation environment for the space weather program. Its scientific data are available for further analysis almost without delay.

Observations of the low earth orbit radiation environment from Mir

Recent measurements of the high-energy charged particle environment with the Radiation Environment Monitor (REM) aboard the Russian Mir space station are presented. Ionizing dose rates in a silicon detector have been measured with two shieldings. The dose is mainly accumulated in two distinct areas, the South Atlantic Anomaly (SAA) and the region of closest approach to the magnetic poles. Whereas the radiation in the South Atlantic Anomaly varied little during 1995, large changes of the daily absorbed doses in the polar regions are observed. A comparison of REM doses with the NASA AP-8 and AE-8 radiation models revealed major differences. AP-8 tends to underestimate the average REM doses, whereas AE-8 overestimates REM doses, and rather describes the worst case.

Modelling of the outer electron belt flux dropout and losses during magnetic storm main phase

Abstract In this paper we analyze the flux dropout and loss of outer belt electrons during magnetic storms. Using observations of the outer belt variation during the 26 March 1995 magnetic storm by the REM detector onboard the STRV-1b satellite, we show that a real loss of electrons occurred during the storm main phase. In order to simulate the outer belt variation during this storm, fully adiabatic motion of equatorial electrons was simulated with the non stationary Tsyganenko96 magnetic field model. We discuss the effect of adiabatic deceleration during the storm main phase and conclude that drift of particles into the magnetopause may be a possible mechanism. Simulations with different field configurations show that the result are sensitive to the various field components.

Radiation environment monitor

Abstract The radiation Environment Monitor (REM) is a modular, programmable monitor for the radiation environment on spacecrafts. REM accumulates differential linear energy transfer spectra of two independent silicon detectors with different shieldings. The instrument is sensitive to protons with energies between 30 MeV and 600 MeV and to electrons with energies between 1 MeV and 10 MeV. During the year 1994 two REM instruments were launched into space, one into a geostationary transfer orbit and one into a low earth orbit. Both instruments are working well and provide simultaneous information on the space radiation environment of different orbits.

High-Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission for the next (2000) solar maximum

The primary scientific objective of the High Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission selected by NASA is to investigate the physics of particle acceleration and energy release in solar flares. Observations will be made of x-rays and (gamma) rays from approximately 3 keV to approximately 20 MeV with an unprecedented combination of high resolution imaging and spectroscopy. The HESSI instrument utilizes Fourier- transform imaging with 9 bi-grid rotating modulation collimators and cooled germanium detectors. The instrument is mounted on a Sun-pointed spin-stabilized spacecraft and placed into a 600 km-altitude, 38 degrees inclination orbit.It will provide the first imaging spectroscopy in hard x-rays, with approximately 2 arcsecond angular resolution, time resolution down to tens of ms, and approximately 1 keV energy resolution; the first solar (gamma) ray line spectroscopy with approximately 1-5 keV energy resolution; and the first solar (gamma) -ray line and continuum imaging,with approximately 36-arcsecond angular resolution. HESSI is planned for launch in July 2000, in time to detect the thousands of flares expected during the next solar maximum.

Outer radiation belt variations during 1995

Abstract The dynamics of the relativistic electron flux in the earths outer radiation belt measured by the Radiation Environment Monitor aborad the STRV-1B satellite is presented from August 1994 to end of April 1996. During this period the earths magnetosphere was driven by recurrent fast solar wind streams which had periodically compressed the magnetosphere and caused large variations of the trapped particle fluxes in the outer radiation belt. The periodic variations are characterized by a rapid depletion, strong and rapid increase and a more steady phase. The flux level reached depends on the velocity of the interacting solar wind stream. The effectiveness of the solar wind — magnetosphere interaction shows a semiannual modulation with a maximum during the equinoxes.