ATHENA X-IFU Research Articles

The Cryogenic AntiCoincidence detector for ATHENA X-IFU: a scientific assessment of the observational capabilities in the hard X-ray band

ATHENA is a large X-ray observatory, planned to be launched by ESA in 2028 towards an L2 orbit. One of the two instruments of the payload is the X-IFU: a cryogenic spectrometer based on a large array of TES microcalorimeters, able to perform integral field spectrography in the 0.2-12 keV band (2.5 eV FWHM at 6 keV). The X-IFU sensitivity is highly degraded by the particle background expected in the L2 orbit, which is induced by primary protons of both galactic and solar origin, and mostly by secondary electrons. To reduce the particle background level and enable the mission science goals, the instrument incorporates a Cryogenic AntiCoincidence detector (CryoAC). It is a 4 pixel TES based detector, placed <1 mm below the main array. In this paper we report a scientific assessment of the CryoAC observational capabilities in the hard X-ray band (E>10 keV). The aim of the study has been to understand if the present detector design can be improved in order to enlarge the X-IFU scientific capability on an energy band wider than the TES array. This is beyond the CryoAC baseline, being this instrument aimed to operate as anticoincidence particle detector and not conceived to perform X-ray observations.

Search for the warm–hot intergalactic medium around A 2744 using Suzaku

Abstract We present the results from Suzaku satellite observations of the surrounding region of a galaxy cluster, A 2744, at z = 0.3. To search for oxygen emission lines from the warm–hot intergalactic medium (WHIM), we analyzed X-ray spectra from two northeastern regions 2.2–3.3 and 3.3–4.4 Mpc from the center of the cluster, which offers the first test on the presence of a WHIM near the typical accretion shock radius (∼2 r200) predicted by hydrodynamical simulations. For the 2.2–3.3 Mpc region, the spectral fit significantly (99.2% significance) improved when we included O vii and O viii lines in the spectral model. A comparable WHIM surface brightness was obtained in the 3.3–4.4 Mpc region and the redshift of the O viii line is consistent with z = 0.3 within errors. The present results support that the observed soft X-ray emission originated from the WHIM. However, considering both statistical and systematic uncertainties, O viii detection in the northeast regions was marginal. The surface brightnesses of the O viii line in 10−7 photons cm−2 s−1 arcmin−2 for the 2.2–3.3 and 3.3–4.4 Mpc regions were measured to be 2.7 ± 1.0 and 2.1 ± 1.2, giving upper limits on the baryon overdensity of δ = 319(&amp;lt; 442) and 284(&amp;lt; 446), respectively. This is comparable with previous observations of cluster outskirts and their theoretical predictions. The future prospect for WHIM detection using the Athena X-IFU micro-calorimeter is briefly discussed here. In addition, we also derived the intracluster medium temperature distribution of A 2744 to detect a clear discontinuity at the location of the radio relic. This suggests that the cluster has undergone strong shock heating by mass accretion along the filament.

Thermal Filters for the ATHENA X-IFU: Ongoing Activities Toward the Conceptual Design

ATHENA is the L2 mission selected by ESA to pursue the science theme “Hot and Energetic Universe.” One of the two focal plane instruments is the X-ray Integral Field Unit, an array of TES microcalorimeters operated at T $$<$$ 100 mK. To allow the X-ray photons focused by the telescope to reach the detector, windows have to be opened on the cryostat thermal shields. X-ray transparent filters need to be mounted on these open windows to attenuate the IR radiation from warm surfaces, to attenuate RF electromagnetic interferences on TES sensors and SQUID electronics, and to protect the detector from contamination. This paper reviews the ongoing activities driving the design of the X-IFU thermal filters.