J. Huovelin

The SMART-1 X-ray solar monitor (XSM): calibrations for D-CIXS and independent coronal science

Abstract The X-ray solar monitor (XSM) is a calibration instrument of the demonstration of compact imaging X-ray spectrometer (D-CIXS) experiment, with a separate Silicon detector unit on the SMART-1 spacecraft. The non-imaging HPSi PIN sensor has a wide field-of-view (FOV) to enable Sun visibility during a significant fraction of the mission lifetime, which is essential for obtaining calibration spectra for the X-ray fluorescence measurements by the imaging D-CIXS spectrometer. The energy range (1– 20 keV ), spectral resolution (about 250 eV at 6 keV ), and sensitivity (about 7000 cps at flux level of 10 −4 W m −2 in the range 1– 8 A ) are tuned to provide optimal knowledge about the Solar X-ray flux on the Lunar surface, matching well with the activating energy range for the fluorescence measured by D-CIXS. The independent science of the XSM will also be valuable, since the XSM energy range is very sensitive to solar flares. The countrate during the top of an X1 flare will be about 35 times higher than the average quiescent countrate at solar maximum. The relative increase will be the same for an M1 flare during the SMART-1 mission, which will be closer to the next solar minimum. Since the XSM will observe the Sun as a star, and the energy range and spectral resolution are close to those of present astronomical X-ray satellites (e.g., XMM-Newton, ASCA, Chandra), we will obtain an X-ray database of the Sun which can be related with the stellar X-ray observations more easily than the data from present solar X-ray instruments. In this publication we give a detailed description of the design, performance, and tasks of the XSM instrument, and view the science perspectives.

Analysis of compounds released from various detector materials and their impact on aging Characteristics of proportional counters

Outgassing properties of various detector materials have been studied. The thermal desorption tube method was used for sampling the compounds released from the materials. Analysis of the samples was carried out with a gas chromatograph/mass spectrometer analyzer. Attention was paid to compounds known to be easily polymerizing. Their impact on the aging characteristics of gaseous radiation detectors was studied by accelerated aging tests with the help of proportional counters. Styrene and some aromatic solvents were observed among the outgassing products of two different polyimide grades. In the accelerated aging tests both the styrene and the aromatic solvents were confirmed to cause a fast gain loss in the proportional counters filled with Ar/CH/sub 4/ gas mixture.

The design of the wide field monitor for the LOFT mission

LOFT (Large Observatory For x-ray Timing) is one of the ESA M3 missions selected within the Cosmic Vision program in 2011 to carry out an assessment phase study and compete for a launch opportunity in 2022-2024. The phase-A studies of all M3 missions were completed at the end of 2013. LOFT is designed to carry on-board two instruments with sensitivity in the 2-50 keV range: a 10 m2 class Large Area Detector (LAD) with a <1° collimated FoV and a wide field monitor (WFM) making use of coded masks and providing an instantaneous coverage of more than 1/3 of the sky. The prime goal of the WFM will be to detect transient sources to be observed by the LAD. However, thanks to its unique combination of a wide field of view (FoV) and energy resolution (better than 500 eV), the WFM will be also an excellent monitoring instrument to study the long term variability of many classes of X-ray sources. The WFM consists of 10 independent and identical coded mask cameras arranged in 5 pairs to provide the desired sky coverage. We provide here an overview of the instrument design, configuration, and capabilities of the LOFT WFM. The compact and modular design of the WFM could easily make the instrument concept adaptable for other missions.

A multiwavelength study of the M dwarf binary YY Geminorum

We review the results of the 1988 multi-wavelength campaign on the late-type eclipsing binary YY Geminorum. Observations include: broadband optical and near infra-red photometry, simultaneous optical and ultraviolet (IUE) spectroscopy, X-ray (Ginga) and radio (VLA) data. From models fitted to the optical light curves, fundamental physical parameters have been determined together with evidence for transient maculations (spots) located near quadrature longitudes and intermediate latitudes. Eclipses were observed at optical, ultraviolet and radio wavelengths. Significant drops in 6cm radio emission near the phases of both primary and secondary eclipse indicate relatively compact radio emitting volumes that may lie between the binary components. IUE observations during secondary eclipse are indicative of a uniform chromosphere saturated with MgII plage-type emission and an extended volume of Ly® emission. Profile fitting of high-dispersion H® spectra confirms the chromospheric saturation and indicates significant H® opacity to heights of a few percent of the photospheric radius. There is evidence for an enhanced H® region visible near phase 0.25-0.35 which may be associated with a large spot on the primary and with two small optical flares which were also observed at other wavelengths: one in microwave radiation and the other in X-rays. For both flares, LX/Lopt is consistent with energy release in closed magnetic structures.

Simulated performance of a single pixel PIN spectrometer SCXM equipped with a concentrator optics in Solar coronal X-ray observations

Abstract In this paper we present simulated solar coronal X-ray observations to verify the sensitivity of a new hypothetical instrument design. These simulations are folded through this X-ray spectrometer having a moderate size circular field of view ( FoV ) of 1.6°. This SCXM (Solar Coronal X-ray Mapper) is designed to compose of a single pixel silicon PIN detector equipped with a single reflection double frustum X-ray optics. A moderate FoV would enable a morphological study of the expanded X-ray emission from the solar corona during a high activity of the Sun. The main scientific task of SCXM would be the mapping of the coronal X-ray emission, i.e. to resolve the radial distribution of the X-ray surface brightness around the Sun. These kinds of off-limb observations would help to interpret the coronal plasma diagnostics as a function of the elongation angle. Direct solar full disc observations could be also performed with SCXM. In this work we have applied real solar coronal X-ray data obtained by the SMART-1 XSM (X-ray Solar Monitor) [3] to simulate on-solar observations at different flux levels to derive full disc sensitivity and performance of SCXM. A challenging attempt for SCXM would also be to distinguish the X-ray spectrum of the decaying axions around the Sun. These axions are assumed to be created as side products of fusion reactions in the core of the Sun. These axions are predicted to be gravitationally trapped to orbit the Sun forming a halo-like X-ray emitting object. No signature of an axion X-ray emission around the Sun has been observed to this day. This simple X-ray spectrometer with an optical concentrator would be an inexpensive instrument with low mass and telemetry budgets compared with more accurate X-ray instruments of imaging capability. Hence SCXM would be an advanced choice as an auxiliary instrument for solar coronal X-ray observations.

Polarimetry of stellar active regions and flares

Observations of regular and irregular polarimetric variability in late-type stars are reviewed, and the related physical and geometrical effects are discussed. There are indications that the irregular part of the variability could be caused by transient events, possibly associated with flares. Polarimetric observations during flares are reviewed, and preliminary results of new observations of a well-known flare star, YY Geminorum, are presented. The results show that the small flare in YY Gem did not cause any significant variations in linear polarization, while the binary eclipse evidently causes an enhancement in the polarization. The reasons for the difficulties in stellar flare polarimetry are discussed. Finally, future prospects for the observations of flaring stars and for the utilization of linear polarimetry as a complementary method to other techniques of surface imaging of stellar activity and flares are presented.