The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of the ESA Athena X-ray observatory. Over a field of view of 5’ equivalent diameter, it will deliver X-ray spectra from 0.2 to 12 keV with a spectral resolution of 2.5 eV up to 7 keV on ∼ 5” pixels. The X-IFU is based on a large format array of super-conducting molybdenum-gold Transition Edge Sensors cooled at ∼ 90 mK, each coupled with an absorber made of gold and bismuth with a pitch of 249 μm. A cryogenic anti-coincidence detector located underneath the prime TES array enables the non X-ray background to be reduced. A bath temperature of ∼ 50 mK is obtained by a series of mechanical coolers combining 15K Pulse Tubes, 4K and 2K Joule-Thomson coolers which pre-cool a sub Kelvin cooler made of a 3He sorption cooler coupled with an Adiabatic Demagnetization Refrigerator. Frequency domain multiplexing enables to read out 40 pixels in one single channel. A photon interacting with an absorber leads to a current pulse, amplified by the readout electronics and whose shape is reconstructed on board to recover its energy with high accuracy. The defocusing capability offered by the Athena movable mirror assembly enables the X-IFU to observe the brightest X-ray sources of the sky (up to Crab-like intensities) by spreading the telescope point spread function over hundreds of pixels. Thus the X-IFU delivers low pile-up, high throughput (< 50%), and typically 10 eV spectral resolution at 1 Crab intensities, i.e. a factor of 10 or more better than Silicon based X-ray detectors. In this paper, the current X-IFU baseline is presented, together with an assessment of its anticipated performance in terms of spectral resolution, background, and count rate capability. The X-IFU baseline configuration will be subject to a preliminary requirement review that is scheduled at the end of 2018.
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.
The X-ray Integral Field Unit (X-IFU) on board the Advanced Telescope for High-ENergy Astrophysics (Athena) will provide spatially resolved high-resolution X-ray spectroscopy from 0.2 to 12 keV, with ~ 5" pixels over a field of view of 5 arc minute equivalent diameter and a spectral resolution of 2.5 eV up to 7 keV. In this paper, we first review the core scientific objectives of Athena, driving the main performance parameters of the X-IFU, namely the spectral resolution, the field of view, the effective area, the count rate capabilities, the instrumental background. We also illustrate the breakthrough potential of the X-IFU for some observatory science goals. Then we brie y describe the X-IFU design as defined at the time of the mission consolidation review concluded in May 2016, and report on its predicted performance. Finally, we discuss some options to improve the instrument performance while not increasing its complexity and resource demands (e.g. count rate capability, spectral resolution).
We present simulations of the detection probability for absorption lines from ions in the warm and hot ionized medium (WHIM) with Athena in the spectra of Gamma-ray burst afterglows. The simulations are based on Swift XRT lightcurves of these afterglows and are performed using the end-to-end simulation framework SIXTE. We simulate both the case of single and multiple absorption lines, as well as results for line searches in absorption structures from a more complex medium. We show that the Athena X-IFU can detect WHIM lines with strong Ovii lines (equivalent widths larger than 0.14 eV) in spectra containing 3 x 106 counts.
The X-ray Integral Field Unit (X-IFU) microcalorimeter, on-board Athena, with its focal plane comprising 3840 Transition Edge Sensors (TESs) operating at 90 mK, will provide unprecedented spectral-imaging capability in the 0.2-12 keV energy range. It will rely on the on-board digital processing of current pulses induced by the heat deposited in the TES absorber, as to recover the energy of each individual events. Assessing the capabilities of the pulse reconstruction is required to understand the overall scientific performance of the X-IFU, notably in terms of energy resolution degradation with both increasing energies and count rates. Using synthetic data streams generated by the X-IFU End-to-End simulator, we present here a comprehensive benchmark of various pulse reconstruction techniques, ranging from standard optimal filtering to more advanced algorithms based on noise covariance matrices. Beside deriving the spectral resolution achieved by the different algorithms, a first assessment of the computing power and ground calibration needs is presented. Overall, all methods show similar performances, with the reconstruction based on noise covariance matrices showing the best improvement with respect to the standard optimal filtering technique. Due to prohibitive calibration needs, this method might however not be applicable to the X-IFU and the best compromise currently appears to be the so-called resistance space analysis which also features very promising high count rate capabilities.
The X-ray spectroscopy telescope Athena has been designed to implement the science theme "the hot and energetic universe", selected by the European Space Agency as the second large mission of its Cosmic Vision program. X-IFU, one of the two interchangeable focal plane instruments of Athena, is a high resolution X-ray spectrometer made of a large array of Transition Edge Sensors. Two options are under consideration for the X-IFU microcalorimeters: Ti/Au bilayers or Mo/Au bilayers. Here we report on our efforts to develop Mo/Au-based TES. The TES are made of high quality superconducting Mo/Au bilayers fabricated at room temperature on low stress Si3N4 membranes; Mo is deposited by RF magnetron sputtering and in-situ covered by a thin (15nm) Au layer deposited by DC sputtering; in a second step, the Au layer thickness is increased ex-situ by e-beam deposition, to obtain suitable resistance Rn and operation temperature values. Very sharp transitions (~few mK transition width) are obtained, with typically Rn~25mΩ and Tc~ 100-120mK for 65/215 bilayers. First simple TES designs are being tested. Also, Bi films several μm thick, intended to constitute the X-ray absorber, are fabricated by electrochemical deposition.
Athena is designed to implement the Hot and Energetic Universe science theme selected by the European Space Agency for the second large mission of its Cosmic Vision program. The Athena science payload consists of a large aperture high angular resolution X-ray optics (2 m2 at 1 keV) and twelve meters away, two interchangeable focal plane instruments: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager. The X-IFU is a cryogenic X-ray spectrometer, based on a large array of Transition Edge Sensors (TES), offering 2:5 eV spectral resolution, with ~5" pixels, over a field of view of 50 in diameter. In this paper, we present the X-IFU detector and readout electronics principles, some elements of the current design for the focal plane assembly and the cooling chain. We describe the current performance estimates, in terms of spectral resolution, effective area, particle background rejection and count rate capability. Finally, we emphasize on the technology developments necessary to meet the demanding requirements of the X-IFU, both for the sensor, readout electronics and cooling chain.
We are developing the digital readout electronics (DRE) of the X-Ray Integral Field Unit (X-IFU), one of the two Athena focal plane instruments. This subsystem is made of two main parts: the DRE-DEMUX and the DRE-EP. With a frequency domain multiplexing (FDM) the DRE-DEMUX makes the readout of the 3 840 Transition Edge Sensors (TES) in 96 channels of 40 pixels each. It provides the AC signals to voltage-bias the TES, it demodulates the detector's data which are readout by a SQUID and low noise amplifiers and it linearizes the detection chain to increase its dynamic range. The feedback is computed with a specific technique, so called baseband feedback (BBFB) which ensures that the loop is stable even with long propagation and processing delays (i.e. a few μs) and with high frequency AC-bias (up to 5 MHz). This processing is partly analogue (anti aliasing and reconstruction filters) but mostly digital. The digital firmware is simultaneously applied to all the pixels in digital integrated circuits. After the demultiplexing the interface between the DRE-DEMUX and the DRE-EP has to cope with a data rate of 61.44 Gbps to transmit the data of the individual pixels. Then, the DRE-EP detects the events and computes their energy and grade according to their spectral quality: low resolution, medium resolution and high resolution (i.e. if two consecutive events are too close the estimate of the energy is less accurate). This processing is done in LEON based processor boards. At its output the DRE-EP provides the control unit of the instrument with a list including for each event its time of arrival, its energy, its location on the focal plane and its grade.
One of the instruments on the Advanced Telescope for High-Energy Astrophysics (Athena) which was one of the three
missions under study as one of the L-class missions of ESA, is the X-ray Microcalorimeter Spectrometer (XMS). This
instrument, which will provide high-spectral resolution images, is based on X-ray micro-calorimeters with Transition
Edge Sensor (TES) and absorbers that consist of metal and semi-metal layers and a multiplexed SQUID readout. The
array (32 x 32 pixels) provides an energy resolution of < 3 eV. Due to the large collection area of the Athena optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. Compared to the requirements for the same instrument on IXO, the performance requirements have been relaxed to fit into the much more restricted boundary conditions of Athena.
In this paper we illustrate some of the science achievable with the instrument. We describe the results of design studies for the focal plane assembly and the cooling systems. Also, the system and its required spacecraft resources will be given.
The EURECA (EURopean-JapanEse Calorimeter Array) project aims to demonstrate the science performance and
technological readiness of an imaging X-ray spectrometer based on a micro-calorimeter array for application in future
X-ray astronomy missions, like Constellation-X and XEUS. The prototype instrument consists of a 5 × 5 pixel array of
TES-based micro-calorimeters read out by by two SQUID-amplifier channels using frequency-domain-multiplexing
(FDM). The SQUID-amplifiers are linearized by digital base-band feedback. The detector array is cooled in a cryogenfree
cryostat consisting of a pulse tube cooler and a two stage ADR. A European-Japanese consortium designs,
fabricates, and tests this prototype instrument. This paper describes the instrument concept, and shows the design and
status of the various sub-units, like the TES detector array, LC-filters, SQUID-amplifiers, AC-bias sources, digital
Initial tests of the system at the PTB beam line of the BESSY synchrotron showed stable performance and an X-ray
energy resolution of 1.58 eV at 250 eV and 2.5 eV @ 5.9 keV for the read-out of one TES-pixel only. Next step is
deployment of FDM to read-out the full array. Full performance demonstration is expected mid 2009.
XEUS is the potential successor to ESA's XMM-Newton X-ray observatory and is being proposed in response to the
Cosmic Vision 2015-2025 long term plan for ESA's Science Programme. A new mission configuration was developed
in the last year, accommodating the boundary conditions of a European-led mission with a formation-flying mirror and
detector spacecraft in L2 with a focal length of 35m and an effective area of >5 m2 at 1 keV. Here the new capabilities
are compared with the key scientific questions presented to the Cosmic Vision exercise: the evolution of large scale
structure and nucleosynthesis, the co-evolution of supermassive black holes and their host galaxies, and the study of
matter under extreme conditions.
XEUS is the potential successor to ESA's XMM-Newton X-ray observatory and is being proposed in response to the Cosmic Vision 2015-2025 long term plan for ESA's Science Programme. Novel light-weight optics with an effective area of 5 m2 at 1 keV and 2 m2 at 7 keV and 2-5" HEW spatial resolution together with advanced detectors will provide much improved imaging, spectroscopic and timing performances and open new vistas in X-ray astronomy in the post 2015 timeframe. XEUS will allow the study of the birth, growth and spin of the super-massive black holes in early AGN, allow the cosmic feedback between galaxies and their environment to be investigated through the study of inflows and outflows and relativistic acceleration and allow the growth of large scale structures and metal synthesis to be probed using the hot X-ray emitting gas in clusters of galaxies and the warm/hot filamentary structures observable with X-ray absorption spectroscopy. High time resolution studies will allow the Equation of State of supra-nuclear material in neutron stars to be constrained. These science goals set very demanding requirements on the mission design which is based on two formation flying spacecraft launched to the second Earth-Sun Lagrangian point by an Ariane V ECA. One spacecraft will contain the novel high performance optics while the other, separated by the 35 m focal length, will contain narrow and wide field imaging spectrometers and other specialized instruments.
EURECA (EURopean-JapanEse Calorimeter Array) comprises a 5 x 5 pixel imaging TES-based micro-calorimeter
array read-out by SQUID-based frequency-domain-multiplexed electronics and cooled down by an adiabatic
demagnetization refrigerator. A European-Japanese consortium designs, fabricates, and tests this prototype instrument
with the aim to show within about 2 years technology readiness of a TES-based X-ray imaging micro-calorimeter array
in anticipation of future X-ray astronomy missions, like XEUS (ESA), Constellation-X (NASA), NEXT (JAXA), DIOS
(JAXA), ESTREMO (ASI), and NEW (Dutch-multinational). This paper describes the instrument concept, and shows
the design of the various sub-units, like the TES detector array, LC-filters, SQUID-amplifiers, flux-locked-loop
electronics, AC-bias sources, etc.
Dark Energy dominates the mass-energy content of the universe (about 73%) but we do not understand it. Most of the remainder of the Universe consists of Dark Matter (23%), made of an unknown particle. The problem of the origin of Dark Energy has become the biggest problem in astrophysics and one of the biggest problems in all of science. The major extant X-ray observatories, the Chandra X-ray Observatory and XMM-Newton, do not have the ability to perform large-area surveys of the sky. But Dark Energy is smoothly distributed throughout the universe and the whole universe is needed to study it. There are two basic methods to explore the properties of Dark Energy, viz. geometrical tests (supernovae) and studies of the way in which Dark Energy has influenced the large scale structure of the universe and its evolution. DUO will use the latter method, employing the copious X-ray emission from clusters of galaxies. Clusters of galaxies offer an ideal probe of cosmology because they are the best tracers of Dark Matter and their distribution on very large scales is dominated by the Dark Energy. In order to take the next step in understanding Dark Energy, viz. the measurement of the 'equation of state' parameter 'w', an X-ray telescope following the design of ABRIXAS will be accommodated into a Small Explorer mission in lowearth orbit. The telescope will perform a scan of 6,000 sq. degs. in the area of sky covered by the Sloan Digital Sky Survey (North), together with a deeper, smaller survey in the Southern hemisphere. DUO will detect 10.000 clusters of galaxies, measure the number density of clusters as a function of cosmic time, and the power spectrum of density fluctuations out to a redshift exceeding one. When combined with the spectrum of density fluctuations in the Cosmic Microwave Background from a redshift of 1100, this will provide a powerful lever arm for the crucial measurement of cosmological parameters.
XEUS is the potential successor to ESA's XMM-Newton X-ray observatory. Novel light-weight optics with an effective area of 10 m2 at 1 keV and 2-5" HEW spatial resolution together with advanced imaging detectors will provide a sensitivity around 200 times better than XMM-Newton as well as much improved high-energy coverage, and spectroscopic performance. This enormous improvement in scientific capability will open up new vistas in X-ray astronomy. It will allow the detection of massive black holes in the earliest AGN and estimates of their mass, spin and red-shift through their Fe-K line properties. XEUS will study the first gravitationally bound, Dark Matter dominated, systems small groups of galaxies and trace their evolution into today's massive clusters. High-resolution spectroscopy of the hot intra-cluster gas will be used to investigate the evolution of metal synthesis to the present epoch. The hot filamentary structure will be studied using absorption line spectroscopy allowing the mass, temperature and density of the intergalactic medium to be characterized. As well as these studies of the deep universe, the enormous low-energy collecting area will provide a unique capability to investigate bright nearby objects with dedicated high-throughput, polarimetric and time resolution detectors.