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.
We present an overview and status update of the 4MOST project at the Final Design Review. 4MOST is a major new wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope at the Paranal Observatory of ESO. Starting in 2022, 4MOST will deploy 2436 optical fibres in a 4.1 square degree field-of-view using a fibre positioner based on the tilting spine principle. The fibres will feed one high-resolution (R~20,000) and two low-resolution (R~5000) spectrographs that all have fixed configuration, 3-channel designs with identical 6k x 6k CCD detectors. Updated performance estimates will be presented based on components already manufactured and pre-production prototypes of critical subsystems.
The 4MOST science goals are mostly driven by a number of large area, space-based observatories of prime European interest: Gaia and PLATO (Galactic Archeology and Stellar Physics), eROSITA (High-Energy Sky), and Euclid (Cosmology and Galaxy Evolution). Science cases based on these observatories, along with wide-area ground-based facilities such as LSST, VISTA and VST drive the ten Consortium Surveys covering a large fraction of the Southern sky, with bright time mostly devoted to the Milky Way disk and bulge areas and the Magellanic Clouds, and the dark/gray time largely devoted to extra-galactic targets. In addition there will be a significant fraction of the fibre-hours devoted to Community Surveys, making 4MOST a true general-purpose survey facility, capable of delivering spectra of samples of objects that are spread over a large fraction of the sky.
The 4MOST Facility Simulator was created to show the feasibility of the innovative operations scheme of 4MOST with all surveys operating in parallel. The simulator uses the mock catalogues created by the science teams, simulates the spectral throughput and detection of the objects, assigns the fibres at each telescope pointing, creates pointing distributions across the sky and simulates a 5-year survey (including overhead, calibration and weather losses), and finally does data quality analyses and computes the science Figure-of-Merits to assess the quality of science produced. The simulations prove the full feasibility of running different surveys in parallel.
When combined with the huge collecting area of the ELT, MOSAIC will be the most effective and flexible Multi-Object Spectrograph (MOS) facility in the world, having both a high multiplex and a multi-Integral Field Unit (Multi-IFU) capability. It will be the fastest way to spectroscopically follow-up the faintest sources, probing the reionisation epoch, as well as evaluating the evolution of the dwarf mass function over most of the age of the Universe. MOSAIC will be world-leading in generating an inventory of both the dark matter (from realistic rotation curves with MOAO fed NIR IFUs) and the cool to warm-hot gas phases in z=3.5 galactic haloes (with visible wavelenth IFUs). Galactic archaeology and the first massive black holes are additional targets for which MOSAIC will also be revolutionary. MOAO and accurate sky subtraction with fibres have now been demonstrated on sky, removing all low Technical Readiness Level (TRL) items from the instrument. A prompt implementation of MOSAIC is feasible, and indeed could increase the robustness and reduce risk on the ELT, since it does not require diffraction limited adaptive optics performance. Science programmes and survey strategies are currently being investigated by the Consortium, which is also hoping to welcome a few new partners in the next two years.
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 an overview of the 4MOST project at the Preliminary Design Review. 4MOST is a major new wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of ESO. 4MOST has a broad range of science goals ranging from Galactic Archaeology and stellar physics to the high-energy physics, galaxy evolution, and cosmology. Starting in 2021, 4MOST will deploy 2436 fibres in a 4.1 square degree field-of-view using a positioner based on the tilting spine principle. The fibres will feed one high-resolution (R~20,000) and two medium resolution (R~5000) spectrographs with fixed 3-channel designs and identical 6k x 6k CCD detectors. 4MOST will have a unique operations concept in which 5-year public surveys from both the consortium and the ESO community will be combined and observed in parallel during each exposure. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing concept, showing that we can expect to observe more than 25 million objects in each 5-year survey period and will eventually be used to plan and conduct the actual survey.
The XMM-Newton observatory, with its high throughput in combination with the EPIC CCD-cameras, is an ideal instrument to study extended sources like clusters of galaxies. Very deep observations of galaxy clusters reveal substructure on different levels: structure associated with bright galaxies, faint galaxies, or structure consistent with the merger of groups with the main cluster. Another indication of substructure is the deviation of the temperature of the intra-cluster gas from isothermality. We present XMM-Newton mosaic observations of the nearby clusters A3667 and A754. These clusters are good representatives of the different evolution stages that all clusters experience as they grow from mergers of smaller groups. Hence they show merging at different phases, which is also reflected in the different appearance of their temperature maps, pressure maps and entropy maps.
We investigated the theoretical performance of a rotating modulation collimator (RMC) situated in front of a moderate angular resolution focusing X-ray telescope. By ray tracing we investigated the RMC's ability to improve the positioning capability and reduce the incidence of source confusion. The moderate angular resolution (two arcmin) telescope can have high collecting area; the factor of four reduction due to the RMC would leave the system with about as much throughput as a high angular resolution telescope of comparable dimensions. This system is likely to be lighter and less costly to construct than a high resolution telescope and could operate over the entire field of a very wide field of view telescope. The wire thickness and spacing are only slightly finer than those of previous RMC's. The effects of possible errors in wire spacing and misalignments of the two wire planes, of the RMC are included in the simulations. Diffraction is also included. Results are encouraging. With 100 detected source counts plus background, we obtain positions with a statistical error below 5 arcseconds. We can resolve and position two, 400-count point sources 25 arcseconds apart. However, this system does not improve upon the telescope resolution in the case of extended sources such as clusters of galaxies.