The particle background of the <Emphasis Type="Italic">X-IFU</Emphasis> instrument

In this paper we are going to review the latest estimates for the particle background expected on the X-IFU instrument onboard of the ATHENA mission. The particle background is induced by two different particle populations: the so called “soft protons” and the Cosmic rays. The first component is composed of low energy particles (< 100s keV) that get funnelled by the mirrors towards the focal plane, losing part of their energy inside the filters and inducing background counts inside the instrument sensitivity band. The latter component is induced by high energy particles (> 100 MeV) that possess enough energy to cross the spacecraft and reach the detector from any direction, depositing a small fraction of their energy inside the instrument. Both these components are estimated using Monte Carlo simulations and the latest results are presented here.     

A systematic analysis of the <Emphasis Type="Italic">XMM-Newton</Emphasis> background: II. Properties of the in-Field-Of-View excess component

We present an accurate characterization of the particle background behaviour on XMM-Newton based on the entire EPIC archive. This corresponds to the largest EPIC data set ever examined. Our results have been obtained thanks to the collaboration between the FP7 European program EXTraS and the ESA R&D ATHENA activity AREMBES. We used as a diagnostic an improved version of the diagnostic which compares the data collected in unexposed region of the detector with the region of the field of view in the EPIC-MOS. We will show that the in Field-of-View excess background is made up of two different components, one associated to flares produced by soft protons and the other one to a low-intensity background. Its origin needs to be further investigated.     

A systematic analysis of the XMM-Newton background: I. Dataset and extraction procedures

XMM-Newton is the direct precursor of the future ESA ATHENA mission. A study of its particle-induced background provides therefore significant insight for the ATHENA mission design. We make use of ～12 years of data, products from the third XMM-Newton catalog as well as FP7 EXTraS project to avoid celestial sources contamination and to disentangle the different components of the XMM-Newton particle-induced background. Within the ESA R&D AREMBES collaboration, we built new analysis pipelines to study the different components of this background: this covers time behavior as well as spectral and spatial characteristics.     

An XMM-Newton proton response matrix

Soft protons constitute an important source of background in focusing X-ray telescopes, as Chandra and XMM-Newton experience has shown. The optics in fact transmit them to the focal plane with efficiency similar to the X-ray photon one. This effect is a good opportunity to study the environment of the Earth magnetosphere crossed by the X-ray satellite orbits, provided that we can link the spectra detected by the instruments with the ones impacting on the optics. For X-ray photons this link has the form of the so-called response matrix that includes the optics effective area and the energy redistribution in the detectors. Here we present a first attempt to produce a proton response matrix exploiting ray-tracing and GEANT4 simulations with the final aim to be able to analyse XMM-Newton soft proton data and link them to the external environment. If the procedure is found to be reliable, it can be applied to any future X-ray missions to predict the soft particles spectra impacting on the focal plane instruments.     

A BeppoSAX Observation of the Merging Cluster Abell 3266

We present results from a BeppoSAX observation of the rich cluster Abell 3266. The broadband spectrum (2-50 keV) of the cluster, when fitted with an optically thin thermal emission model, yields a temperature of 8.1+/-0.2 keV and a metal abundance of 0.17+/-0.02 in solar units, with no evidence of a hard X-ray excess in the Phoswich Detector System spectrum. By performing a spatially resolved spectral analysis, we find that the projected temperature drops with increasing radius, going from approximately 10 keV at the cluster core to approximately 5 keV at about 1.5 Mpc. Our BeppoSAX temperature profile is in good agreement with the ASCA temperature profile of Markevitch et al. From our two-dimensional temperature map, we find that the gradient is observed in all azimuthal directions. The temperature gradient may have been caused by a recent merger event that was also responsible for a velocity-dispersion gradient measured in the optical band. The projected metal abundance profile and the two-dimensional map are both consistent with being constant.     

Interaction in Abell 2256: The BeppoSAX View

Precision Doppler measurements from the Keck High-Resolution Echelle Spectrograph reveal periodic Keplerian velocity variations in the stars HD 16141 and HD 46375. HD 16141 (G5 IV) has a period of 75.8 days and a velocity amplitude of 11 m s-1, yielding a companion having Msini=0.22 M(JUP) and a semimajor axis of a=0.35 AU. HD 46375 (K1 IV-V) has a period of 3.024 days and a velocity amplitude of 35 m s-1, yielding a companion with Msini=0.25 M(JUP), a semimajor axis of a=0.041 AU, and an eccentricity of 0.04 (consistent with zero). These companions contribute to the rising planet mass function toward lower masses.     

Hard X-Ray Emission from the Galaxy Cluster A2256

After the positive detection by BeppoSAX of hard X-ray radiation up to approximately 80 keV in the Coma Cluster spectrum, we present evidence for nonthermal emission from A2256 in excess of thermal emission at a 4.6 sigma confidence level. In addition to this power-law component, a second nonthermal component already detected by ASCA could be present in the X-ray spectrum of the cluster, which is not surprising given the complex radio morphology of the cluster central region. The spectral index of the hard tail detected by the Phoswich Detection System on board BeppoSAX is marginally consistent with that expected for the inverse Compton model. A value of approximately 0.05 μG is derived for the intracluster magnetic field of the extended radio emission in the northern regions of the cluster, while a higher value of approximately 0.5 μG could be present in the central radio halo, which is likely related to the hard tail detected by ASCA.     

BeppoSAX–ROSAT PSPC observations of the Shapley supercluster: A3562

We present a combined analysis of the BeppoSAX and ROSAT PSPC observation of the cluster of galaxies A3562, a massive member of the core of the Shapley supercluster. With a complex and interacting structure composed from two groups of galaxies and A3558 to the west, the surface brightness of A3562 shows excess in the sectors to east and south when compared with an azimuthally averaged model of the emission. The emission tends to be flatter, and the distribution of the gas broader, along the merging axis and in opposition to the two groups. We present the first determination of the gradients of the gas temperature and metallicity for a cluster in the Shapley region at large distance from the cluster centre. From an analysis of the BeppoSAX data in annuli and sectors, we observe both the profiles to be flat within 8 arcmin (∼0.62 Mpc), with emission-weighted values of kT =5.1±0.2 keV and Z =0.39±0.05 Z_⊙. The value of the temperature is consistent with recent ASCA measurements and is significantly higher than previous estimates obtained from ROSAT and EXOSAT . We discuss the possible reasons for this disagreement. Between 8 and 20 arcmin, the plasma temperature declines to about 3.2 keV. When a polytropic profile is used to represent the gas temperature profile, the best-fitting polytropic index is 1.16±0.03. These results imply a total mass within the virial radius of between 40 and 80 per cent lower than the optical estimate, and a gas mass fraction of about 30 per cent.     

Soft proton flux on <Emphasis Type="Italic">ATHENA</Emphasis> focal plane and its impact on the magnetic diverter design

The experience gained with the current generation of X-ray telescopes like Chandra and XMM-Newton has shown that low energy “soft” protons can pose a severe threat to the possibility to exploit scientific data, reducing the available exposure times by up to 50% and introducing a poorly reproducible background component. These soft protons are present in orbits outside the radiation belts and enter the mirrors, being concentrated towards the focal plane instruments, losing energy along their path and finally depositing their remaining energy in the detectors. Their contribution to the residual background will be even higher for ATHENA with respect to previous missions, given the much higher collecting area of the mirrors, even if the instruments will likely suffer no significant radiation damage from this particles flux. As a consequence this soft proton flux shall be damped with the use of a magnetic diverter to avoid excess background loading on the WFI or X-IFU instruments. We present here a first complete evaluation of this background component for the two focal plane instruments of the ATHENA mission in absence of a magnetic diverter, and derive the requirements for such device to reduce the soft protons induced background below the level required to enable the mission science. We estimate the soft proton flux expected in L2 for the interplanetary component and for the component generated locally by acceleration processes in the magnetotail. We produce a proton response matrix for each of the two instruments of ATHENA focal plane, exploiting two independent Monte Carlo simulations to estimate the optics concentration efficiency, and Geant4 simulations to evaluate the energy loss inside the radiation filters and deposited in the detector. With this modular approach we derive the expected fluxes and spectra for the soft protons component of the background. Finally, we calculate the specifics of a magnetic diverter able to reduce such flux below the required level for both X-IFU and WFI.     

A systematic analysis of the XMM-Newton background: IV

We show the results obtained in the FP7 European program EXTraS and in the ESA R&D ATHENA activity AREMBES aimed at a deeper understanding of the XMM-Newton background to better design the ATHENA mission. Thanks to an analysis of the full EPIC archive coupled to the information obtained by the Radiation Monitor we show the cosmic ray origin of the unfocused particle background and its anti-correlation with the solar activity. We show the first results of the effort to obtain informations about the particle component of the soft proton focused background.