The Large Observatory For x-ray Timing (LOFT) is a mission concept which was proposed to ESA as M3 and M4 candidate in the framework of the Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behaviour of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, >8m2 effective area, 2-30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the current technical and programmatic status of the mission.
A scintillation gamma-ray detector, composed of a commercial 0.5" thick, 0.5" diameter LaBr3(Ce) crystal coupled to a 7-cell hexagonal Silicon Drift Detector has been developed and tested. The characterization with X-rays and gamma rays is presented and discussed also within the context of the optical properties of the readout system. A final comparison between our results and state of the art is also discussed in order to propose this prototype for astrophysical applications.
A future compact and modular X and gamma-ray spectrometer (XGS) has been designed and a series of proto- types have been developed and tested. The experiment envisages the use of CsI scintillator bars read out at both ends by single-cell 25 mm2 Silicon Drift Detectors. Digital algorithms are used to discriminate between events absorbed in the Silicon layer (lower energy X rays) and events absorbed in the scintillator crystal (higher energy X rays and -rays). The prototype characterization is shown and the modular design for future experiments with possible astrophysical applications (e.g. for the THESEUS mission proposed for the ESA M5 call) are discussed.
The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final downselection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supranuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m2 effective area, 2-30 keV, 240 eV spectral resolution, 1° collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study.
LOFT (Large Observatory for X-ray Timing) is one of the five candidates that were considered by ESA as an M3 mission (with launch in 2022-2024) and has been studied during an extensive assessment phase. It is specifically designed to perform fast X-ray timing and probe the status of the matter near black holes and neutron stars. Its pointed instrument is the Large Area Detector (LAD), a 10 m2-class instrument operating in the 2-30keV range, which holds the capability to revolutionise studies of variability from X-ray sources on the millisecond time scales.
The LAD instrument has now completed the assessment phase but was not down-selected for launch. However, during the assessment, most of the trade-offs have been closed leading to a robust and well documented design that will be reproposed in future ESA calls. In this talk, we will summarize the characteristics of the LAD design and give an overview of the expectations for the instrument capabilities.
The LOFT mission concept is one of four candidates selected by ESA for the M3 launch opportunity as Medium Size missions of the Cosmic Vision programme. The launch window is currently planned for between 2022 and 2024. LOFT is designed to exploit the diagnostics of rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultradense matter. These primary science goals will be addressed by a payload composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a collimated (<1 degree field of view) experiment operating in the energy range 2-50 keV, with a 10 m2 peak effective area and an energy resolution of 260 eV at 6 keV. The WFM will operate in the same energy range as the LAD, enabling simultaneous monitoring of a few-steradian wide field of view, with an angular resolution of <5 arcmin. The LAD and WFM experiments will allow us to investigate variability from submillisecond QPO’s to yearlong transient outbursts. In this paper we report the current status of the project.
The Large Observatory for X-ray Timing (LOFT) is one of the four candidate ESA M3 missions considered for launch in
the 2022 timeframe. It is specifically designed to perform fast X-ray timing and probe the status of the matter near black
holes and neutron stars. The LOFT scientific payload is composed of a Large Area Detector (LAD) and a Wide Field
Monitor (WFM). The LAD is a 10 m2-class pointed instrument with 20 times the collecting area of the best past timing
missions (such as RXTE) over the 2-30 keV range, which holds the capability to revolutionize studies of X-ray
variability down to the millisecond time scales. Its ground-breaking characteristic is a low mass per unit surface,
enabling an effective area of ~10 m2 (@10 keV) at a reasonable weight. The development of such large but light
experiment, with low mass and power per unit area, is now made possible by the recent advancements in the field of
large-area silicon detectors - able to time tag an X-ray photon with an accuracy <10 μs and an energy resolution of ~260
eV at 6 keV - and capillary-plate X-ray collimators. In this paper, we will summarize the characteristics of the LAD
instrument and give an overview of its capabilities.
The use of large-area, fine-pitch Silicon detectors has demonstrated the feasibility of wide field imaging experiments
requesting very low resources in terms of weight, volume, power and costs. The flying SuperAGILE instrument
is the first such experiment, adopting large-area Silicon microstrip detectors coupled to one-dimensional
coded masks. With less than 10 kg, 12 watt and 0.04 m3 it provides 6-arcmin angular resolution over >1 sr field
of view. Due to odd operational conditions, SuperAGILE works in the unfavourable energy range 18-60 keV. In
this paper we show that the use of innovative large-area Silicon Drift Detectors allows to design experiments with
arcmin-imaging performance over steradian-wide fields of view, in the energy range 2-50 keV, with spectroscopic
resolution in the range of 300-570 eV (FWHM) at room temperature. We will show the concept, design and
readiness of such an experiment, supported by laboratory tests on large-area prototypes. We will quantify the
expected performance in potential applications on X-ray astronomy missions for the observation and long-term
monitoring of Galactic and extragalactic transient and persistent sources, as well as localization and fine study
of the prompt emission of Gamma-Ray Bursts in soft X-rays.
In the context of the design of wide-field of view experiments for X-ray astronomy, we studied the response to X-rays in
the range between 2 and 60 keV of a large area Silicon Drift Chamber originally designed for particle tracking in high
energy physics. We demonstrated excellent imaging and spectroscopy performance of monolithic 53 cm2 detectors, with
position resolution as good as 30 μm and energy resolution in the range 300-570 eV FWHM obtainable at room
temperature (20 °C). In this paper we show the results of test campaigns at the X-ray facility at INAF/IASF Rome, aimed
at characterizing the detector performance by scanning the detector area with highly collimated spots of monochromatic
X-rays. In these tests we used a detector prototype equipped with discrete read-out front-end electronics.
The X-ray sky in high time resolution holds the key to a number of observables related to fundamental physics,
inaccessible to other types of investigations, such as imaging, spectroscopy and polarimetry. Strong gravity effects, the
measurement of the mass of black holes and neutron stars, the equation of state of ultradense matter are among the
objectives of such observations. The prospects for future, non-focused X-ray timing experiments after the exciting age of
RXTE/PCA are very uncertain, mostly due to the technological limitations that need to be faced to realize experiments
with effective areas in the range of several square meters, meeting the scientific requirements. We are developing large-area
monolithic Silicon drift detectors offering high time and energy resolution at room temperature, with modest
resources and operation complexity (e.g., read-out) per unit area. Based on the properties of the detector and read-out
electronics we measured in laboratory, we built a concept for a realistic unprecedented large mission devoted to X-ray
timing in the energy range 2-30 keV. We show that effective areas in the range of 10-15 square meters are within reach,
by using a conventional spacecraft platform and launcher.
A new micro scanner CT for small animals - based on a couple of parallel quasi-monochromatic X-ray beams with different energies selectable - is under development. The aim of the study is the in vivo imaging of the tumor neo-angiogenesis pattern in an earlier diagnostic phase and the analysis of cancer growth and metastasis development in different tumor types on mice. As previously demonstrated1, the imaging system based on dual energy quasi- monochromatic X-ray beams provides higher sensitivity in detecting low concentrations of iodine contrast medium if compared to traditional polychromatic X-ray equipment. The K-edge dual energy radiology is a realistic candidate to recognize tumor neo- angiogenesis process in a very earlier stage, in which conventional systems are very poor in sensitivity. Moreover, the capability to select the energy of quasi-monochromatic beams enables the use of the Multi-Energy Quasi-Monochromatic technique. Tuning properly the energies allows maximizing the difference between linear absorption coefficients of healthy and pathological tissues increasing the contrast of pathologies. In order to optimize the contrast with this technique, one should know the X-ray energy regions where the absorption of healthy and pathological tissues eventually differs and that for each type of tumor under study. For this reason, the systematic X-ray characterization of many types of healthy and neoplastic human and mice tissues is in progress. The goal of this work is to obtain a catalog of liner attenuation coefficients of a variety of pathological tissues for respect to the healthy ones, finding any energy windows of radiological differentiation. In this paper, the theoretical methods are presented with development works and preliminary results.
In angiography practice an iodate contrast medium is injected in patient vessels with catheters. The absorption of x-rays raises immediately after the iodine K-edge energy. In digital subtraction angiography, two images are used, acquired before and after the injection of the contrast medium, respectively. The vessels morphology result from the difference of images so obtained. This technique involves a non-negligible risk of morbidity or mortality, due to high concentration of injected contrast agent. We are investigating a new source which produces two thin parallel quasi-monochromatic beams - having peak energies centered before and after the iodine K-edge energy, respectively - by using a conventional x-ray tube and a highly oriented pyrolytic graphite mosaic crystal. The polychromatic x-rays incident on the crystal are monochromatized by Bragg diffraction and split in two thin parallel beams, by means of a collimating system. These two beams impinge on the phantom simulating patient vessels and are detected with solid-state array detectors. The image results as difference between the remaining intensities of two beams. We report a preliminary study of the new technique performed both with theoretical stimulations and experimental measurements. Results of computer simulation give information about characteristics as size and quality of the quasi- monochromatic beams, that should be considered in detail to design a system dedicated to the clinical practice. Experimental measurements have been performed on a small- field detector in order to shows the enhancement of image contrast obtained with the application of the new technique.
A small prototype cadmium telluride (CdTe) detector optimized for the detection of gamma-rays having an energy of the order of 500 keV was designed. This detector was arranged as an array of 5x5 CdTe crystals, each having dimensions of 2x2x10 cu mm, and was constructed primarily in order to verify its technical feasibility and performances. The initial aim in developing this type of detector was for use in space applications such as measurement of annihilation radiation (511 keV photons) from the galactic center and possibly from extragalactic objects as for example AGN's (Active Galactic Nucleus). Many other applications may also benefit from the use of CdTe position sensitive detectors, in linear or square configuration, such as nuclear medicine diagnostics, nondestructive testing in industrial quality assurance processes, and safety inspection and controls.