Estimate of the impact of background particles on the X-Ray Microcalorimeter Spectrometer on IXO

We present the results of a study on the impact of particles of galactic (GCR) and solar origin for the X-ray Microcalorimeter Spectrometer (XMS) aboard an astronomical satellite flying in an orbit at the second Lagrangian point (L2). The detailed configuration presented in this paper is the one adopted for the International X-Ray Observatory (IXO) study, however the derived estimates can be considered a conservative limit for ATHENA, that is the IXO redefined mission proposed to ESA. This work is aimed at the estimate of the residual background level expected on the focal plane detector during the mission lifetime, a crucial information in the development of any instrumental configuration that optimizes the XMS scientific performances. We used the Geant4 toolkit, a Monte Carlo based simulator, to investigate the rejection efficiency of the anticoincidence system and assess the residual background on the detector.Comment: 18 pages, 9 figure

The LOFT (Large Observatory for X-ray Timing) background simulations

The Large Observatory For X-ray Timing (LOFT) is an innovative medium-class mission selected for an assessment phase in the framework of the ESA M3 Cosmic Vision call. LOFT is intended to answer fundamental questions about the behaviour of matter in the very strong gravitational and magnetic fields around compact objects. With an effective area of ~10 m^2 LOFT will be able to measure very fast variability in the X-ray fluxes and spectra. A good knowledge of the in-orbit background environment is essential to assess the scientific performance of the mission and to optimize the instrument design. The two main contributions to the background are cosmic diffuse X-rays and high energy cosmic rays; also, albedo emission from the Earth is significant. These contributions to the background for both the Large Area Detector and the Wide Field Monitor are discussed, on the basis of extensive Geant-4 simulations of a simplified instrumental mass model.Comment: Proceedings of SPIE, Vol. 8443, Paper No. 8443-209, 201

Measurement of the effect of Non Ionising Energy Losses on the leakage current of Silicon Drift Detector prototypes for the LOFT satellite

The silicon drift detectors are at the basis of the instrumentation aboard the Large Observatory For x-ray Timing (LOFT) satellite mission, which underwent a three year assessment phase within the "Cosmic Vision 2015 - 2025" long-term science plan of the European Space Agency. Silicon detectors are especially sensitive to the displacement damage, produced by the non ionising energy losses of charged and neutral particles, leading to an increase of the device leakage current and thus worsening the spectral resolution. During the LOFT assessment phase, we irradiated two silicon drift detectors with a proton beam at the Proton Irradiation Facility in the accelerator of the Paul Scherrer Institute and we measured the increase in leakage current. In this paper we report the results of the irradiation and we discuss the impact of the radiation damage on the LOFT scientific performance.Comment: 21 pages, 7 figures, 2 tables. Accepted for publication by Journal of Instrumentation (JINST

Hyper-velocity impact test and simulation of a double-wall shield concept for the Wide Field Monitor aboard LOFT

The space mission LOFT (Large Observatory For X-ray Timing) was selected in 2011 by ESA as one of the candidates for the M3 launch opportunity. LOFT is equipped with two instruments, the Large Area Detector (LAD) and the Wide Field Monitor (WFM), based on Silicon Drift Detectors (SDDs). In orbit, they would be exposed to hyper-velocity impacts by environmental dust particles, which might alter the surface properties of the SDDs. In order to assess the risk posed by these events, we performed simulations in ESABASE2 and laboratory tests. Tests on SDD prototypes aimed at verifying to what extent the structural damages produced by impacts affect the SDD functionality have been performed at the Van de Graaff dust accelerator at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg. For the WFM, where we expect a rate of risky impacts notably higher than for the LAD, we designed, simulated and successfully tested at the plasma accelerator at the Technical University in Munich (TUM) a double-wall shielding configuration based on thin foils of Kapton and Polypropylene. In this paper we summarize all the assessment, focussing on the experimental test campaign at TUM.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray, 91446

A magnetic electron repeller to improve the ATHENA/WFI background level

The WFI is a DEPFET-based device developed at MPE as one of the two focal plane instruments for the next large ESA's mission for high energy astrophysics ATHENA. The expected level of instrumental background induced by the radiation environment in space is one of the parameters driving the camera design and it is required to be below 5∙10 cts/cm2 /sec/keV to enhance some of the unique observing capabilities of this detector. Background reduction can be obtained in a passive way by optimizing the detector shielding specifications (e.g. materials, thicknesses) and discarding frame regions affected by X-ray-like counts. In principle a higher rejection efficiency could be achieved with an active anticoincidence system surrounding the detector, in practice this cannot be done as it would make very complicated the camera readout and introduce dead-time. In this proceeding we discuss how a passive shielding against soft electrons with efficiency comparable to that of an active anticoincidence and no dead-time issue could be obtained by means of permanent magnets. We present results of a very preliminary feasibility study conducted in the framework of AHEAD and demonstrate theoretically the effectiveness of this solution. Nevertheless, an actual implementation would have as drawbacks an increased mass of the camera due to the presence of magnets and a potentially disturbing residual field in the detector environment

Radiation tests of the Silicon Drift Detectors for LOFT

During the three years long assessment phase of the LOFT mission, candidate to the M3 launch opportunity of the ESA Cosmic Vision programme, we estimated and measured the radiation damage of the silicon drift detectors (SDDs) of the satellite instrumentation. In particular, we irradiated the detectors with protons (of 0.8 and 11 MeV energy) to study the increment of leakage current and the variation of the charge collection efficiency produced by the displacement damage, and we "bombarded" the detectors with hypervelocity dust grains to measure the effect of the debris impacts. In this paper we describe the measurements and discuss the results in the context of the LOFT mission.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray, 91446

In-orbit background of X-ray microcalorimeters and its effects on observations

Methods.There are no experimental data about the background experienced by microcalorimeters in the L2 orbit, and thus the particle background levels were calculated by means of Monte Carlo simulations: we considered the original design configuration and an improved configuration aimed to reduce the unrejected background, and tested them in the L2 orbit and in the low Earth orbit, comparing the results with experimental data reported by other X-ray instruments.To show the results obtainable with the improved configuration we simulated the observation of a faint, high-redshift, point source (F[0.5-10 keV]~6.4E-16 erg cm-2 s-1, z=3.7), and of a hot galaxy cluster at R200 (Sb[0.5-2 keV]=8.61E-16 erg cm-2 s-1 arcmin-2,T=6.6 keV). Results.First we confirm that implementing an active cryogenic anticoincidence reduces the particle background by an order of magnitude and brings it close to the required level.The implementation and test of several design solutions can reduce the particle background level by a further factor of 6 with respect to the original configuration.The best background level achievable in the L2 orbit with the implementation of ad-hoc passive shielding for secondary particles is similar to that measured in the more favorable LEO environment without the passive shielding, allowing us to exploit the advantages of the L2 orbit.We define a reference model for the diffuse background and collect all the available information on its variation with epoch and pointing direction.With this background level the ATHENA mission with the X-IFU instrument is able to detect ~4100 new obscured AGNs with F>6.4E-16 erg cm-2 s-1 during three years, to characterize cluster of galaxies with Sb(0.5-2 keV)>9.4E-16 erg cm-2 s-1 sr-1 on timescales of 50 ks (500 ks) with errors <40% (<12%) on metallicity,<16% (4.8%) on temperature,2.6% (0.72%) on the gas density, and several single-element abundances.Comment: the PDF has poor quality, it will be improved in the futur

The Microchannel X-ray Telescope for the Gamma-Ray Burst mission SVOM

We present the Microchannel X-ray Telescope, a new light and compact focussing telescope that will be flying on the Sino-French SVOM mission dedicated to Gamma-Ray Burst science. The MXT design is based on the coupling of square pore micro-channel plates with a low noise pnCCD. MXT will provide an effective area of about 50 cmsq, and its point spread function is expected to be better than 3.7 arc min (FWHM) on axis. The estimated sensitivity is adequate to detect all the afterglows of the SVOM GRBs, and to localize them to better then 60 arc sec after five minutes of observation.Comment: 12 pages, 8 figures, to be published in SPIE Astronomical Telescopes + Instrumentation, Montreal, June 201

The Microchannel X-ray Telescope on Board the SVOM Satellite

We present the Micro-channel X-ray Telescope (MXT), a new narrow-field (about 1{\deg}) telescope that will be flying on the Sino-French SVOM mission dedicated to Gamma-Ray Burst science, scheduled for launch in 2021. MXT is based on square micro pore optics (MPOs), coupled with a low noise CCD. The optics are based on a "Lobster Eye" design, while the CCD is a focal plane detector similar to the type developed for the seven eROSITA telescopes. MXT is a compact and light (<35 kg) telescope with a 1 m focal length, and it will provide an effective area of about 45 cmsq on axis at 1 keV. The MXT PSF is expected to be better than 4.2 arc min (FWHM) ensuring a localization accuracy of the afterglows of the SVOM GRBs to better than 1 arc min (90\% c.l. with no systematics) provided MXT data are collected within 5 minutes after the trigger. The MXT sensitivity will be adequate to detect the afterglows for almost all the SVOM GRBs as well as to perform observations of non-GRB astrophysical objects. These performances are fully adapted to the SVOM science goals, and prove that small and light telescopes can be used for future small X-ray missions.Comment: 6 pages, 6 figures, proceedings of the conference "Swift: 10 years of Discovery", Rome, December 2-5, 2014. To be published by Po

Monte-Carlo Simulations of the Suzaku-XRS Residual Background Spectrum

Cryogenic micro-calorimeters are suitable to detect small amounts of energy deposited by electromagnetic and nuclear interactions, which makes them attractive in a variety of applications on ground and in space. The only X-ray microcalorimeter that operated in orbit to date is the X-Ray Spectrometer on-board of the Japanese Suzaku satellite. We discuss the analysis of the components of its residual background spectrum with the support of Monte-Carlo simulations