XIPE, the X-ray Imaging Polarimetry Explorer, is a mission dedicated to X-ray Astronomy. At the time of
writing XIPE is in a competitive phase A as fourth medium size mission of ESA (M4). It promises to reopen the
polarimetry window in high energy Astrophysics after more than 4 decades thanks to a detector that efficiently
exploits the photoelectric effect and to X-ray optics with large effective area. XIPE uniqueness is time-spectrally-spatially-
resolved X-ray polarimetry as a breakthrough in high energy astrophysics and fundamental physics.
Indeed the payload consists of three Gas Pixel Detectors at the focus of three X-ray optics with a total effective
area larger than one XMM mirror but with a low weight. The payload is compatible with the fairing of the Vega
launcher. XIPE is designed as an observatory for X-ray astronomers with 75 % of the time dedicated to a Guest
Observer competitive program and it is organized as a consortium across Europe with main contributions from
Italy, Germany, Spain, United Kingdom, Poland, Sweden.
Minimization of charged particle background in X-ray telescopes is a well known issue. Charged particles (chiefly
protons and electrons) naturally present in the cosmic environment constitute an important background source when
they collide with the X-ray detector. Even worse, a serious degradation of spectroscopic performances of the X-ray
detector was observed in Chandra and Newton-XMM, caused by soft protons with kinetic energies ranging between 100
keV and some MeV being collected by the grazing-incidence mirrors and funneled to the detector. For a focusing
telescope like SIMBOL-X, the exposure of the soft X-ray detector to the proton flux can increase significantly the
instrumental background, with a consequent loss of sensitivity. In the worst case, it can also seriously compromise the
detector duration. A well-known countermeasure that can be adopted is the implementation of a properly-designed
magnetic diverter, that should prevent high-energy particles from reaching the focal plane instruments of SIMBOL-X.
Although Newton-XMM and Swift-XRT are equipped with magnetic diverters for electrons, the magnetic fields used
are insufficient to effectively act on protons. In this paper, we simulate the behavior of a magnetic diverter for
SIMBOL-X, consisting of commercially-available permanent magnets. The effects of SIMBOL-X optics is simulated
through GEANT4 libraries, whereas the effect of the intense required magnetic fields is simulated along with
specifically-written numerical codes in IDL.
The 10-100 keV region of the electromagnetic spectrum contains the potential for a dramatic improvement in our understanding of a number of key problems in high energy astrophysics. A deep inspection of the universe in this band is on the other hand still lacking because of the demanding sensitivity (fraction of μCrab in the 20-40 keV for 1 Ms integration time) and imaging (≈ 15" angular resolution) requirements. The mission ideas currently being proposed are based on long focal length, grazing incidence, multi-layer optics, coupled with focal plane detectors with few hundreds μm spatial resolution capability. The required large focal lengths, ranging between 8 and 50 m, can be realized by means of extendable optical benches (as foreseen e.g. for the HEXITSAT, NEXT and NuSTAR missions) or formation flight scenarios (e.g. Simbol-X and XEUS). While the final telescope design will require a detailed trade-off analysis between all the relevant parameters (focal length, plate scale value, angular resolution, field of view, detector size, and sensitivity degradation due to detector dead area and telescope vignetting), extreme attention must be dedicated to the background minimization. In this respect, key issues are represented by the passive baffling system, which in case of large focal lengths requires particular design assessments, and by the active/passive shielding geometries and materials. In this work, the result of a study of the expected background for a hard X-ray telescope is presented, and its implication on the required sensitivity, together with the possible implementation design concepts for active and passive shielding in the framework of future satellite missions, are discussed.
The INTEGRAL gamma-ray observatory is due to be launched in October 2002 on a Proton rocket from the Russian base in Baikonur in Kazakhstan. Its scientific payload contains two main instruments on board, one dedicated to spectrometry (SPI) and with moderate imaging capabilities, and the other (IBIS) designated to produce high angular resolution images with moderate energy resolution, in addition to X-ray and Optical monitors. The IBIS telescope itself consists of two main subsystem: a low energy (15 keV - 1 MeV) detector (ISGRI) and a plane (PICsIT) working at higher energies (170 keV - 10 MeV). Both these instruments use the same coded aperture mask in order to create images of the sky over the entire energy range with a resolution of 12 arcminutes and point source location accuracy down to tens of arcseconds for the strongest sources. The data from the satellite will be trasmitted to the INTEGRAL Science Data Centre (ISDC) located near Geneva for initial processing and distribution of the analysis results. The quantity of data is large, and each observation will typically consist of many individual pointings around the target, which will then be summed together. This allows a reduction of systematic effects in the creation of the spectral imaging images. Herein we describe the data structure of the PICsIT instrument from raw low-level data through to the high-level scientific products, indicating how the data sets are used to obtain images and spectra for celestial gamma-ray sources.
INTEGRAL is the forthcoming European Space Agency's (ESA) satellite mission for gamma-ray astronomy, which will be launched in 2002. IBIS is the imaging telescope onboard INTEGRAL and will produce images of the gamma-ray sky in the region between 15 keV and 10 MeV by means of a two-layer position sensitive detection plane coupled with a coded aperture mask. The detection plane of IBIS comprises two detectors: ISGRI, operative in the 15 keV - 1 MeV range, and PICsIT, 150 keV - 10 MeV. The PICsIT instrument, which is the high energy plane of the IBIS imager, comprises 8 individual modules of 512 detection elements. The modules are arranged in a 4 x 2 pattern, while the pixels are in a 16 x 32 array within each module. Detailed simulation programs of PICsIT qualification and flight model have been set up in order to provide a complete scientific characterization of the detector in terms of spectral and imaging performances. These simulation programs have also been used to reproduce the on-ground calibration results, and will be the basis for the production of the response matrix.