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.
Since 2015, AHEAD (Integrated Activities in the High Energy Astrophysics Domain) has provided a reference framework to bring together Europe's science community. AHEAD is part of the EU Horizon 2020 programme for Research Infrastructures. Its main goal is to integrate the national efforts and keep the European community at the cutting edge of science and technology. AHEAD is offering funding opportunities, also open to participants outside Europe, for transnational visits, workshops and dissemination activities. The landmark for AHEAD is the future large observatory Athena. Significant effort is devoted to improve its design beyond the baseline and improve the related infrastructures. AHEAD is also active in the exploitation of current space missions, providing access to data archives and advanced tools and delivering new products and services. Finally, it supports technology innovation for the benefits of society and new design studies towards the definition of a future gamma-ray mission.
The development of a Laue lens to focus soft gamma rays appears today as the only solution to improve significantly telescopes’ sensitivity and angular resolution in the 100 keV – 1 MeV domain. A Laue lens makes use of diffraction in the volume of a large number of crystal tiles carefully orientated to concentrate incident radiations from a large collecting area in a small focal spot. Various type of crystal have been measured and show excellent results, with angular spread of diffracting planes in the range 15-45 arcsec, and reflectivities up to 31 % at 600 keV. Precision of orientation of crystals is demanding because of the long focal length involved by small angles of diffraction. A prototype currently being built by a French collaboration including the CESR, the CNES and Thales Alenia Space aims to achieve 10 arcsec of tolerance.
We present an overview of the set of celestial sources used for in-flight calibration of x-ray detectors by past and operational missions. We show the rationale behind their choice as a guideline for future missions aiming at optimizing the critical early phases of their science operations.
On 28 november 2013 ESA selected “The Hot and Energetic Universe” as the scientific theme for a large mission to be flown in 2028 in the second lagrangian point, and ATHENA is the mission that will address this science topic. It will carry on board the X-ray Integral Field Unit (X-IFU), a 3840 pixel array based on TES (Transition Edge Sensor) microcalorimeters providing high resolution spectroscopy (2.5 eV @ 6 keV) in the 0.3-12 keV range. Among X-IFU goals there is the detection and characterization of high redshift AGNs, Clusters of galaxies and their outskirts, and the elusive Warm Hot Intergalactic Medium (WHIM), so great care must be paid to the reduction of the background level. These scientific objectives will be reached if the particle background is kept lower than 0.05 cts cm<sup>−2</sup> s<sup>−1</sup>, and to this aim, it is mandatory the use of a Cryogenic AC (CryoAC), as well as an optimized design of the cryostat and of the structures surrounding X-IFU. Our team, that is responsible for the ACD design, performed a detailed study to predict the rejection efficiency of the ACD as a function of its geometrical parameters and design choices. Since no experimental data on the background experienced by X-Ray microcalorimeters in the L2 orbit are available at the moment, the particle background levels have been calculated by means of Monte Carlo simulations using the Geant4 software.
“The Hot and Energetic Universe” is the scientific theme approved by the ESA SPC for a Large mission to be flown in the next ESA slot (2028th) timeframe. ATHENA is a space mission proposal tailored on this scientific theme. It will be the first X-ray mission able to perform the so-called “Integral field spectroscopy”, by coupling a high-resolution spectrometer, the X-ray Integral Field Unit (X-IFU), to a high performance optics so providing detailed images of its field of view (5’ in diameter) with an angular resolution of 5” and fine energy-spectra (2.5eV@E<7keV). The X-IFU is a kilo-pixel array based on TES (Transition Edge Sensor) microcalorimeters providing high resolution spectroscopy in the 0.2-12 keV range. Some goals is the detection of faint and diffuse sources as Warm Hot Intergalactic Medium (WHIM) or galaxies outskirts. To reach its challenging scientific aims, it is necessary to shield efficiently the X-IFU instrument against background induced by external particles: the goal is 0.005 cts/cm^2/s/keV. This scientific requirement can be met by using an active Cryogenic AntiCoincidence (CryoAC) detector placed very close to X-IFU (~ 1 mm below). This is shown by our GEANT4 simulation of the expected background at L2 orbit. The CryoAC is a TES based detector as the X-IFU sharing with it thermal and mechanical interfaces, so increasing the Technology Readiness Level (TRL) of the payload. It is a 2x2 array of microcalorimeter detectors made by Silicon absorber (each of about 80 mm^2 and 300 μm thick) and sensed by an Ir TES. This choice shows that it is possible to operate such a detector in the so-called athermal regime which gives a response faster than the X-IFU (< 30 μs), and low energy threshold (above few keV). Our consortium has developed and tested several samples, some of these also featured by the presence of Al-fins to efficiently collect the athermal phonons, and increased x-ray absorber area (up to 1 cm^2). Here the results of deep test related to one of the last sample produced (namely AC-S5), and steps to reach the final detector design will be discussed.
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.
We present several solutions to reduce the background that will be experienced by the X-ray Microcalorimeter
Spectrometer (XMS) aboard of the ATHENA mission due to Galactic Cosmic Rays (GCR) and solar particles present in
the second Lagrangian point L2. The configuration presented in this paper is the one adopted for the International X-ray
Observatory (IXO) but the derived estimates can be considered a conservative limit for ATHENA, that is the IXO
redefined mission proposed to ESA. We used the Geant4 toolkit, a Monte Carlo based simulator, to investigate the
rejection efficiency of the anticoincidence system and assess the residual background on the detector. Even though the
mission did not pass the down selection of ESA, this work lay the basis of a study for a microcalorimeters-based mission
The capability of NuSTAR to detect polarization in the Compton scattering regime (>50 keV) has been investigated. The
NuSTAR mission, flown on June 2012 a Low Earth Orbit (LEO), provides a unique possibility to confirm the findings of
INTEGRAL on the polarization of cosmic sources in the hard X-rays. Each of the two focal plane detectors are high
resolution pixellated CZT arrays, sensitive in the energy range ~ 3 - 80 keV. These units have intrinsic polarization
capabilities when the proper information on the double events is transmitted on ground. In this case it will be possible to
detect polarization from bright sources on timescales of the order of 10<sup>5</sup> s
ATHENA has been the re-scoped IXO mission, and one of the foreseen focal plane instrument was the X-ray Microcalorimeter Spectrometer (XMS) working in the energy range 0.3-10 keV, which was a kilo-pixel array based on TES (Transition Edge Sensor) detectors. The need of an anticoincidence (AC) detector is legitimated by the results performed with GEANT4 simulations about the impact of the non x-ray background onto XMS at L2 orbit (REQ. < 0.02 cts/cm2/s/keV). Our consortium has both developed and tested seveal samples, with increasing area, in order to match the large area of the XMS (64 mm2). Here we show the preliminary results from the last prototype. The results achieved in this work offer a solution to reduce the particle background not only for the presently study mission, but also for any satellite/balloon borne instrument that foresees a TES-based microcalorimeters/bolometers focal plane (from millimeter to x-ray domain).
The Energetic X-ray Imaging Survey Telescope (EXIST) is designed to i) use the birth of stellar mass black holes, as
revealed by cosmic Gamma-Ray Bursts (GRBs), as probes of the very first stars and galaxies to exist in the Universe.
Both their extreme luminosity (~10<sup>4</sup> times larger than the most luminous quasars) and their hard X-ray detectability over
the full sky with wide-field imaging make them ideal "back-lights" to measure cosmic structure with X-ray, optical and
near-IR (nIR) spectra over many sight lines to high redshift. The full-sky imaging detection and rapid followup narrowfield
imaging and spectroscopy allow two additional primary science objectives: ii) novel surveys of supermassive black
holes (SMBHs) accreting as very luminous but rare quasars, which can trace the birth and growth of the first SMBHs as
well as quiescent SMBHs (non-accreting) which reveal their presence by X-ray flares from the tidal disruption of
passing field stars; and iii) a multiwavelength Time Domain Astrophysics (TDA) survey to measure the temporal
variability and physics of a wide range of objects, from birth to death of stars and from the thermal to non-thermal
Universe. These science objectives are achieved with the telescopes and mission as proposed for EXIST described here.
The <i>EXIST</i> mission has been recently re-designed prior to being proposed to the ASTRO2010 Decadal Survey. One of
the most recent improvements has been the addition of a third instrument consisting of a powerful Soft X-ray Imager
(SXI) that will study in detail and help characterizing the high energy sources detected by the High Energy Telescope
(HET). The <i>EXIST</i> concept fully exploits the heritage of Swift in the fast follow-up of transients and in particular GRBs,
with 10 to 20 times more sensitivity in the high energy band (from 0.2 to 600 keV) and exceptional performance in the
near-IR/optical provided by the Infrared Telescope (IRT). SXI has an important role in extending by more than one
decade in energy, down to the soft X-rays the coverage of HET. Such combination will be fully exploited when
performing pointed observations. Within the <i>EXIST</i> follow-up program, foreseen during the second part of the mission,
SXI and HET will be able to collect high quality spectra for thousands of sources covering the energy range 0.1-
hundreds keV. Furthermore, while working in survey mode SXI will cover about half the sky in 2 years and will be able
to improve the location accuracy of many faint HET sources (reducing the positional uncertainty from 20 arcsec to ~ 1-2
arcsec). In this paper we will address the performance and the main scientific contributions expected from SXI.
The hard X-ray sky now being studied by <i>INTEGRAL</i> and <i>Swift</i> and soon by <i>NuSTAR</i> is rich with energetic phenomena
and highly variable non-thermal phenomena on a broad range of timescales. The High Energy Telescope (HET) on the
proposed Energetic X-ray Imaging Survey Telescope (<i>EXIST</i>) mission will repeatedly survey the full sky for rare and
luminous hard X-ray phenomena at unprecedented sensitivities. It will detect and localize (<20", at 5σ threshold) X-ray
sources quickly for immediate followup identification by two other onboard telescopes - the Soft X-ray imager (SXI)
and Optical/Infrared Telescope (IRT). The large array (4.5 m<sup>2</sup>) of imaging (0.6 mm pixel) CZT detectors in the HET, a
coded-aperture telescope, will provide unprecedented high sensitivity (~0.06 mCrab Full Sky in a 2 year continuous
scanning survey) in the 5 - 600 keV band. The large field of view (90° × 70°) and zenith scanning with alternating-orbital
nodding motion planned for the first 2 years of the mission will enable nearly continuous monitoring of the full
sky. A 3y followup pointed mission phase provides deep UV-Optical-IR-Soft X-ray and Hard X-ray imaging and
spectroscopy for thousands of sources discovered in the Survey. We review the HET design concept and report the
recent progress of the CZT detector development, which is underway through a series of balloon-borne wide-field hard
X-ray telescope experiments, <i>ProtoEXIST</i>. We carried out a successful flight of the first generation of fine pixel large
area CZT detectors (<i>ProtoEXIST1</i>) on Oct 9, 2009. We also summarize our future plan (<i>ProtoEXIST2</i> & <i>3</i>) for the
technology development needed for the HET.
The Energetic X-ray Imaging Survey Telescope (EXIST) will continuously survey the full sky in scanning mode for 2-
years followed by a 3-years pointing phase. The mission includes three instruments: a High Energy coded mask
Telescope; a 1.1m aperture optical-IR Telescope; and a Soft X-ray Imager (SXI), sensitive in the 0.1-10 keV band. SXI
is proposed as a contribution of ASI-Italy, fully developed by Italian institutes. Here we will present the optical and
mechanical design of the SXI mirror module, that includes also a pre-collimator and a magnetic diverter to ensure a low
background on the detector. In particular we will describe the mirror module characteristics in term of effective area,
imaging capability, thermal requirement and mechanical properties. The current optical design foresees 26 shells
providing an effective area comparable to one XMM-Newton mirror module up to 3 keV. The realization of these shells
is based on the well-proven Nickel replication-process technology.
The Energetic X-ray Imaging Survey Telescope (EXIST) mission, submitted to the Decadal Survey, is a
multiwavelength observatory mainly devoted to the study of Super Massive Black Holes, Gamma Ray Bursts and other
transient sources. The set of instruments foreseen for EXIST includes a soft x-ray telescope (SXI), proposed as a
contribution of the Italian Space Agency (ASI).
We present the baseline design of the X-Ray camera for SXI telescope, that we have finalized under ASI contract. The
camera is based on a focal plane detector consisting of a 450 μm thick silicon pixel sensor sensitive, with high QE, in the
full SXI range (0.1-10 KeV), and capable of high energy resolution when operated in photon counting mode (E/dE ~ 47
at 6 keV), frame rate ~ 100-200 frames/s (enabling timing in the ms range), and spatial resolution matching the optical
characteristics of the mirror module. We provide an overview of the mechanical, thermal and electrical concept of the
The EXIST observatory planned for launch in the next decade will carry outstanding contributions in both Galactic and
Extragalactic science with a sensitivity about 10-20 better respect to the flown hard X-ray missions and full sky survey
capability. Designed mainly for the survey of SMBH and transients, thanks to the wide field of view (~70x90deg) and
large effective area of the High Energy Telescope (HET), the study of spectra and variability at all timescales of all types
of Galactic sources will be made possible. EXIST will be also capable to study in detail the Galactic Center (GC) in the
hard X-rays. This crowded region as observed recently by Chandra, Integral and Swift has been found to possibly host a
high number of high energy sources. In this work we report on the capabilities of EXIST to image the GC region and to
detect and characterize the different classes of sources on the basis of their known spectral and variability properties.
EXIST will perform the crucial observation tests to study the emission from Sgr A*, using the simultaneous observations
of IR and X-ray flares, searching for periodicity to study the Keplerian flow with NIR and/or X QPO, confirm or not the
high energy counterpart of SgrA* detected by INTEGRAL and define the spectral shape of the high energy tail. Finally,
EXIST can effectively and continuously monitor spectra from Sgr B2 to confirm the correlation of the iron line emission
with the hard X-ray continuum and establish its origin.
We present a study of the background for the array of microcalorimeters onboard of the International X-ray
Observatory space mission. We investigated through simulations the rates at the focal plane of soft and hard
particles in L2 orbit. Assuming the presence of an anticoincidence instrument, we derived an estimate of the
residual background. The preliminary results reported in this paper are based on a number of simplifications of
the actual picture. Efforts to improve the model are on-going.
The paper describes the SIDERALE experiment that was hosted as a piggy back payload on SoRa LDB (Sounding Radar
Long Distance Balloon) mission by the Italian Space Agency (ASI). SIDERALE was aimed at testing a detector for high
energy astrophysics applications based on a 4x4 pixel CZT solid state sensor. An onboard data handling computer, a
mass memory and a power supply units were integrated in SIDERALE. Furthermore an innovative telemetry system BIT
(Bi-directional Iridium Telemetry) was used in order for SIDERALE to be autonomous and independent from the
hosting payload. In the paper a preliminary analysis of flight and scientific data is discussed.
The technique which combines high resolution spectroscopy with imaging capability is a powerful tool to extract
fundamental information in X-ray Astrophysics and Cosmology. TES (Transition Edge Sensors)-based
microcalorimeters match at best the requirements for doing fine spectroscopy and imaging of both bright (high count
rate) and faint (poor signal-to-noise ratio) sources. For this reason they are considered among the most promising
detectors for the next high energy space missions and are being developed for use on the focal plane of the IXO
(International X-ray Observatory) mission. In order to achieve the required signal-to-noise ratio for faint or diffuse
sources it is necessary to reduce the particle-induced background by almost two orders of magnitude. This reduction can
only be achieved by adopting an active anticoincidence technique. In this paper, we will present a novel anticoincidence
detector based on a TES sensor developed for the IXO mission. The pulse duration and the large area of the IXO TESarray
(XMS X-ray Microcalorimeter Spectrometer) require a proper design of the anticoincidence detector. It has to
cover the full XMS area, yet delivering a fast response. We have therefore chosen to develop it in a four-pixel design.
Experimental results from the large-area pixel prototypes will be discussed, also including design considerations.
We report on the development of a 3D position sensitive prototype suitable as focal plane detector for Laue lens
telescope. The basic sensitive unit is a drift strip detector based on a CZT crystal, (~19×8 mm<sup>2</sup> area, 2.4 mm thick),
irradiated transversally to the electric field direction. The anode side is segmented in 64 strips, that divide the crystal in 8
independent sensor (pixel), each composed by one collecting strip and 7 (one in common) adjacent drift strips. The drift
strips are biased by a voltage divider, whereas the anode strips are held at ground. Furthermore, the cathode is divided in
4 horizontal strips for the reconstruction of the third interaction position coordinate. The 3D prototype will be made by
packing 8 linear modules, each composed by one basic sensitive unit, bonded on a ceramic layer. The linear modules
readout is provided by a custom front end electronics implementing a set of three RENA-3 for a total of 128 channels.
The front-end electronics and the operating logics (in particular coincidence logics for polarisation measurements) are
handled by a versatile and modular multi-parametric back end electronics developed using FPGA technology.
Laue lenses are an emerging technology based on diffraction in crystals that allows the concentration of soft
gamma rays. This kind of optics that works in the 100 keV - 1.5 MeV band can be used to realize an highsensitivity
and high-angular resolution telescope (in a narrow field of view). This paper reviews the recent
progresses that have been done in the development of efficient crystals, in the design study and in the modelisation
of the answer of Laue lenses. Through the example of a new concept of 20 m focal length lens focusing in the 100
keV - 600 keV band, the performance of a telescope based on a Laue lens is presented. This lens, uses the most
efficient mosaic crystals in each sub-energy range in order to yield the maximum reflectivity. Imaging capabilities
are investigated and shows promising results.
The Energetic X-ray Imaging Survey Telescope (EXIST) is a mission that has been studied for the NASA Physics of the
Cosmos Program. EXIST will continuously survey the full sky by scanning for 2-years (with 2-3 interruptions per day
for GRB follow-up) followed by a 3-years pointing phase. The mission includes three instruments: a High Energy coded
mask Telescope; a 1.1m aperture optical-IR Telescope; and a Soft X-ray Imager (SXI), sensitive in the 0.1-10 keV band.
SXI is proposed as a contribution of ASI-Italy, fully developed by Italian institutes. The current optical design foresees
26 shells providing an effective area comparable to one XMM-Newton mirror module up to 3 keV and somewhat lower
from 3 to 10 keV. The realization of these shells is based on the well-proven Nichel replication-process technology. Here
we will present the optical design of the SXI mirror module and describe its characteristics in term of effective area and
imaging capability, summarizing also the characteristics of the full SXI telescope.
The SXI telescope is one of the three instruments on board EXIST, a multiwavelenght observatory in charge of
performing a global survey of the sky in hard X-rays searching for Supermassive Black Holes. One of the primary
objectives of EXIST is also to study with unprecedented sensitivity the most unknown high energy sources in
the Universe, like high redshift GRBs, which will be pointed promptly by the Spacecraft by autonomous trigger
based on hard X-ray localization on board. The recent addition of a soft X-ray telescope to the EXIST payload
complement, with an effective area of 950 cm<sup>2</sup> in the energy band 0.2-3 keV and extended response up to 10 keV
will allow to make broadband studies from 0.1 to 600 keV. In particular, investigations of the spectra components
and states of AGNs and monitoring of variability of sources, study of the prompt and afterglow emission of GRBs
since the early phases, which will help to constrain the emission models and finally, help the identification of
sources in the EXIST hard X-ray survey and the characterization of the transient events detected. SXI will also
perform surveys: a scanning survey with sky coverage ~ 2 π and limiting flux of ~ 5 × 10<sup>-14</sup> cgs plus other
serendipitous. We give an overview of the SXI scientific performance and also describe the status of its design
emphasizing how it has been derived by the scientific requirements.
The science drivers for a new generation soft gamma-ray mission are naturally focused on the detailed study of
the acceleration mechanisms in a variety of cosmic sources. Through the development of high energy optics in the
energy energy range 0.05-1 MeV it will be possible to achieve a sensitivity about two orders of magnitude better
than the currently operating gamma-ray telescopes. This will open a window for deep studies of many classes of
sources: from Galactic X-ray binaries to magnetars, from supernova remnants to Galaxy clusters, from AGNs
(Seyfert, blazars, QSO) to the determination of the origin of the hard X-/gamma-ray cosmic background, from
the study of antimatter to that of the dark matter. In order to achieve the needed performance, a detector with
mm spatial resolution and very high peak efficiency is needed. The instrumental characteristics of this device
could eventually allow to detect polarization in a number of objects including pulsars, GRBs and bright AGNs. In
this work we focus on the characteristics of the focal plane detector, based on CZT or CdTe semiconductor sensors
arranged in multiple planes and viewed by a side detector to enhance gamma-ray absorption in the Compton
regime. We report the preliminary results of an optimization study based on simulations and laboratory tests,
as prosecution of the former design studies of the GRI mission which constitute the heritage of this activity.
The importance of hard X-ray astronomy (>10 keV) is now widely recognized. Recently both ESA and NASA have
indicated in their guidelines for the progress of X- and γ-ray astronomy in the next decade the development of new
instrumentation working in the energy range from the keV to the MeV region, where important scientific issues are still
open, exploiting high sensitivity for spectroscopic imaging and polarimetry observations. The development of new
concentrating (e.g. multilayer mirror) telescopes for hard X-rays (10 -100 keV) and focusing instruments based on Laue
lenses operating from ~60 keV up to a few MeV is particularly challenging. We describe the design of a threedimensional
(3D) depth-sensing position sensitive device suitable for use as the basic unit of a high efficiency focal
plane detector for a Laue lens telescope. The sensitive unit is a drift strip detector based on a CZT crystal, (10×10 mm<sup>2</sup>
area, 2.5 mm thick), irradiated transversally to the electric field direction. The anode is segmented into 4 detection cells,
each comprising one collecting strip and 8 drift strips. The drift strips are biased by a voltage divider, whereas the anode
strips are held at 0 V. The cathode is divided in 4 horizontal strips for the reconstruction of the Z interaction position.
The 3D prototype will be made by packing 8 linear modules, each composed of 2 basic sensitive units, bonded onto a
ceramic layer together with the readout electronics.
How structures of various scales formed and evolved from the early Universe up to present time is a fundamental
question of astrophysics. EDGE will trace the cosmic history of the baryons from the early generations of massive
stars by Gamma-Ray Burst (GRB) explosions, through the period of galaxy cluster formation, down to the very low
redshift Universe, when between a third and one half of the baryons are expected to reside in cosmic filaments undergoing
gravitational collapse by dark matter (the so-called warm hot intragalactic medium). In addition EDGE, with its
unprecedented capabilities, will provide key results in many important fields. These scientific goals are feasible with a
medium class mission using existing technology combined with innovative instrumental and observational capabilities
by: (a) observing with fast reaction Gamma-Ray Bursts with a high spectral resolution (R ~ 500). This enables the study
of their (star-forming) environment and the use of GRBs as back lights of large scale cosmological structures; (b)
observing and surveying extended sources (galaxy clusters, WHIM) with high sensitivity using two wide field of view
X-ray telescopes (one with a high angular resolution and the other with a high spectral resolution). The mission concept
includes four main instruments: a Wide-field Spectrometer with excellent energy resolution (3 eV at 0.6 keV), a Wide-
Field Imager with high angular resolution (HPD 15") constant over the full 1.4 degree field of view, and a Wide Field
Monitor with a FOV of <sup>1</sup>/<sub>4</sub> of the sky, which will trigger the fast repointing to the GRB. Extension of its energy response
up to 1 MeV will be achieved with a GRB detector with no imaging capability. This mission is proposed to ESA as part
of the Cosmic Vision call. We will briefly review the science drivers and describe in more detail the payload of this
The success of the SWIFT/BAT and INTEGRAL missions has definitely opened a new window for follow-up
and deep study of the transient gamma-ray sky. This now appears as the access key to important progresses in
the area of cosmological research and deep understanding of the physics of compact objects. To detect in near
real-time explosive events like Gamma-Ray bursts, thermonuclear flashes from Neutron Stars and other types of
X-ray outbursts we have developed a concept for a wide-field gamma-ray coded mask instrument working in the
range 8-200 keV, having a sensitivity of 0.4 ph cm<sup>−2</sup> s<sup>−1</sup> in 1 s (15-150 keV) and arcmin location accuracy over
a sky region as wide as 3 sr. This scientific requirement can be achieved by means of two large area, high spatial
resolution CZT detection planes made of arrays of relatively large (~ 1 cm<sup>2</sup>) crystals, which are in turn read
out as matrices of smaller pixels. To achieve such a wide Field-Of-View the two units can be placed at the sides
of a S/C platform serving a payload with a complex of powerful X-ray instruments, as designed for the EDGE
mission. The two units will be equipped with powerful signal read out system and data handling electronics,
providing accurate on-board reconstruction of the source positions for fast, autonomous target acquisition by
the X-ray telescopes.
In the context of R&D studies financed by the Italian Space Agency (ASI), a feasibility study to evaluate the Italian
Industry interest in medium-large scale production of enhanced CZT detectors has been performed by an Italian
Consortium. The R&D investment aims at providing in-house source of high quality solid state spectrometers for Space
Astrophysics applications. As a possible spin-off industrial applications to Gamma-ray devices for non-destructive
inspections in medical, commercial and security fields have been considered by ASI. The short term programme mainly
consists of developing proprietary procedures for 2-3" CZT crystals growth, including bonding and contact philosophy,
and a newly designed low-power electronics readout chain. The prototype design and breadboarding is based on a fast
signal AD conversion with the target in order to perform a new run for an already existing low-power (<0.7 mW/pixel)
ASIC. The prototype also provides digital photon energy reconstruction with particular care for multiple events and
polarimetry evaluations. Scientific requirement evaluations for Space Astrophysics Satellite applications have been
carried out in parallel, targeted to contribute to the ESA Cosmic Vision 2015-2025 Announcement of Opportunity.
Detailed accommodation studies are undergoing, as part of this programme, to size a "Large area arcsecond angular
resolution Imager" for the Gamma Ray Imager satellite (Knödlseder et al., this conference).and a new Gamma-ray Wide
Field Camera for the "EDGE" proposal (Piro et al., this conference). Finally, an extended market study for cost analysis
evaluation in view of the foreseen massive detector production has been performed.
The development of formation flying technology in space has opened a new window for astronomy at hard X-γ-ray
wavelenghts, allowing observations with unprecedented angular resolution (location accuracy of the order of few
arcsec). This has stimulated the development of new concepts for imaging instruments: on one side, the focusing
telescopes like γ-ray lens, using small,well shielded detector volumes, on the other side very large area γ-ray
imagers, both allowing a big step in sensitivity. We report on a study for the concept of a large area (1 square
meter), narrow field coded mask telescope with arcsec imaging capability, based on CZT detector technology
and active collimation system, made of Si microstrip detector modules and operating in the energy band 15-500
keV. Feasibility and performance characteristics are discussed as well as possible geometric configurations and
background suppression schemes, in the light of data obtained from INTEGRAL/IBIS and other CdTe/CZT
instruments currently in space.
We present a mission designed to address two main themes of the ESA Cosmic Vision Programme: the Evolution of the Universe and its Violent phenomena. ESTREMO/WFXRT is based on innovative instrumental and observational approaches, out of the mainstream of observatories of progressively increasing area, i.e.: Observing with fast reaction transient sources, like GRB, at their brightest levels, thus allowing high resolution spectroscopy. Observing and surveying through a X-ray telescope with a wide field of view and with high sensitivity extended sources, like cluster and Warm Hot Intragalactic Medium (WHIM). ESTREMO/WFXRT will rely on two cosmological probes: GRB and large scale X-ray structures. This will allow measurements of the dark energy, of the missing baryon mass in the local universe, thought to be mostly residing in outskirts of clusters and in hot filaments (WHIM) accreting onto dark matter structures, the detection of first objects in the dark Universe, the history of metal formation. The key asset of ESTREMO/WFXRT with regard to the study of Violent Universe is the capability to observe the most extreme objects of the Universe during their bursting phases. The large flux achieved in this phase allows unprecedented measurements with high resolution spectroscopy. The mission is based on a wide field X-ray/hard X-ray monitor, covering >1/4 of the sky, to localize transients; fast (min) autonomous follow-up with X-ray telescope (2000 cm<sup>2</sup>) equipped with high resolution spectroscopy transition edge (TES) microcalorimeters (2eV resolution below 2 keV) and with a wide field (1°) for imaging with 10" resolution (CCD) extended faint structures and for cluster surveys. A low background is achieved by a 600 km equatorial orbit. The performances of the mission on GRB and their use as cosmological beacons are presented and discussed.
The outstanding scientific performances of IBIS, Imager on Board INTEGRAL, has encouraged preliminary feasibility studies on new Gamma Ray instruments. We considered both a Wide Field Camera for transient event detection and fast automatic sky localisation and a high resolution imager. According to the basic scientific requirements, i.e. to operate with good sensitivity (1mCrab/day) and spatial resolution (from arcmin to arcsec) on a wide energy range (5 to 500 keV), these studies consider large detector area (from 1 to several m<sup>2</sup>) and a high number (~50000) of thick (≥ 5mm) pixels. Recent achievements already obtained by INTEGRAL, and initially showed by SWIFT, have validated the CdTe/CZT detector performances in terms of good spatial resolution, detection efficiency, energy resolution and low noise at room temperature. We have started a study to solve peculiar problems affecting this kind of detectors (e.g. response dependent on the interaction depth and multiple hit events) using a digital approach to photon reconstruction. This also facilitates operations like pixel to pixel equalisation and background rejection. The detector electronic chain thus includes a minimal analog stage for charge pre-amplification, coupled to a flash ADC for waveform digitalisation at a high time resolution sampling, and a powerful, FPGA based digital processing unit, devoted to waveform elaboration. Such a design should also help in optimising the telemetry flux and allow polarimetry evaluation on multiple events.
The mission concept MAX is a space borne crystal diffraction telescope, featuring a broad-band Laue lens optimized for the observation of compact sources in two wide energy bands of high astrophysical relevance. For the first time in this domain, gamma-rays will be focused from the large collecting area of a crystal diffraction lens onto a very small detector volume. As a consequence, the background noise is extremely low, making possible unprecedented sensitivities. The primary scientific objective of MAX is the study of type Ia supernovae by measuring intensities, shifts and shapes of their nuclear gamma-ray lines. When finally understood and calibrated, these profoundly radioactive events will be crucial in measuring the size, shape, and age of the Universe. Observing the radioactivities from a substantial sample of supernovae and novae will significantly improve our understanding of explosive nucleosynthesis. Moreover, the sensitive gamma-ray line spectroscopy performed with MAX is expected to clarify the nature of galactic microquasars (e<sup>+</sup>e<sup>-</sup> annihilation radiation from the jets), neutrons stars and pulsars, X-ray Binaries, AGN, solar flares and, last but not least, gamma-ray afterglow from gamma-burst counterparts.
To follow up on the remarkable discoveries of the Compton Gamma Ray Observatory and GRANAT, the International Gamma Ray Astrophysics Laboratory (INTEGRAL) mission was selected by ESA as part of the agency's 'HORIZON 2000' strategic plan. It is scheduled to begin detailed gamma ray spectral and imaging studies, of unprecedented resolution, in the year 2001. One of the two main INTEGRAL instruments is a high performance imager. It features a coded aperture mask and a novel large area multilayer detector which utilizes both cadmium telluride and cesium iodide elements to deliver the fine angular-resolution approximately 12 arcmin, wide spectral response (15 keV to 10 MeV) and high resolution spectroscopy (6% at 100 keV) required to satisfy the mission's imaging objectives.
A passive shield will be implemented on the IBIS instrument in order to reduce at low and medium energies the cosmic diffuse background and the source fluxes contribution outside the field of view. The collimator device originally proposed has been reviewed against an alternative option consisting of a box-type lateral shield. Advantages and disadvantages of the two system are analyzed in view of different optimization criteria including background, sensitivity and imaging performance as a function of energy.
The MART-LIME is a large area x-ray experiment planned to be launched on board the Russian satellite Spectrum X-Gamma, as the high energy imager of a complement of broad band co- aligned x-ray telescopes. The energy range covered is 5 - 150 keV with an angular resolution of 8.6 arcminutes. The final detector configuration is now in its testing phase and includes the high pressure window comprising the 6 by 6 degree collimator, and the multiwire proportional counter (MWPC). The response to x-ray sources was investigated during the tests carried out at the Daresbury Laboratory (Warrington, UK) facilities The MWPC was filled up by a xenon-argon-isobutane gas mixture in order to evaluate the efficiency of the detector and in particular its linearity over the whole approximately 2,000 cm<SUP>2</SUP> sensitive area. At the same time the various parts of the apparatus have been simulated by using a Monte Carlo program. Results on the detector response and simulations are presented.
IAS, a CNR institute for space research in Astrophysics, in collaboration with IKI on their invitation, has developed, and is now under building, an X-Ray Imaging and Spectroscopic telescope as the high energy instrument on board the Observatory Spectrum X-Gamma. The scientific aim of this instrument, named MART-LIME, will be the detailed study of X-Ray sources emitting in the energy range 5 - 150 keV. The MART-LIME telescope is a follow up in a series of X-Ray detectors that have been developed, built at IAS and flown on board stratospheric balloons. It consists of a high pressure gas operated multiwire proportional counter with bidimensional spectral resolution coupled with a coded mask placed at 2.3 meter.