The ASTENA mission concept under study in the framework of the H2020 AHEAD project includes a wide field monitor and spectrometer (WFM/S), mainly dedicated to GRBs. The instrument, composed by different units, is sensitive in the range 1 keV – 20 MeV. The total isotropic detection area will be ~3.0 m2 with a FOV of about 1.35 sr. The WFM will allow the detection and spectroscopic and polarimetric characterization of all classes of GRBs. Each module is a coded mask telescope that will allow the source localization within few arcmin up to 50–100 keV. The detector core is based on the coupling of low-noise, solid-state Silicon Drift Detectors (SDDs) with CsI(Tl) scintillator bars. Low-energy and highenergy photons are discriminated using the on-board electronics. The instrument design and preliminary experimental characterizations are reported and discussed.
Within the AHEAD consortium a mission concept named ASTENA (Advanced Surveyor of Transient Events and Nuclear Astrophysics) is proposed to address the top-priority themes identified by the AHEAD Science Advisory Group: Gamma-Ray Bursts and Nuclear Astrophysics. GRBs are among the most intriguing phenomena of the Universe, which thanks to their vast luminosities can be used to probe the first billion years of cosmic history, i.e. the era of first stars and black-holes. In spite of great advancements in the GRB astronomy since the BeppoSAX discovery of afterglows, several issues concerning both the prompt emission and the afterglow are still open. Concerning the prompt emission, for example, the emission mechanism of the radiation and the energy dissipation site (internal shocks? external shocks? photosphere?) are far from being understood. What is required is an accurate determination of the photon spectrum from few keV up to tens of MeV, and importantly, a measurement of the polarization of the radiation. The emission of the afterglow has been deeply investigated with Swift in the energy band from 0.5 to 10 keV, showing that an understanding of the origin of the emission mechanism requires spectral information extending to much higher energies, as already suggested by a few studies at < 60 keV (e.g., Kouveliotou et al. 2013, ApJ 779, L1). Landmark progress on this issue therefore requires polarization capabilities and a passband extending well beyond 60 keV.
Concerning nuclear astrophysics, a fundamental issue concerns the origin of the 511 keV positron annihilation line discovered with INTEGRAL/SPI in the Galactic center. According to the INTEGRAL results the emission is diffuse, but the poor imaging capability of INTEGRAL (at the best with a resolution of 12 arcmin with ISGRI) does not allow one to establish whether what appears diffuse is indeed the superposition of the emission from point-like sources, such as micro-quasars. The important role played by micro-quasars as sources of positron annihilation line emission has also been established with INTEGRAL (Siegert et al. 2016, Nature 531, 341). Another open issue in nuclear astrophysics concerns the determination and understanding of the nuclear burning processes in Type-1a supernovae. This requires a study of the intensity and time behavior of the expected lines emitted by the heavy elements produced in supernova explosions. Instrument concept to address the IWG requirements.
With the above considerations in mind, we propose to perform a feasibility study of a configuration of two instruments:
a) a wide field monitor/spectrometer (WFM/S), with a passband from 1 keV to 20 MeV, made of a
suitable number of detection modules, each consisting of an array of long bars of scintillator with very small cross section, and readout from both sides with solid state thin detectors (e.g. Silicon Drift Detectors, SDD). One of the SDD is used as soft X-ray Position Sensitive Detector. A possible crystal material is CsI(Tl), but also other faster crystals such as LSO(Ce) or CeBr3 should be examined. The detector modules are coupled to a light coded mask, for obtaining a GRB localization accuracy of order of ~1 arcmin between 1 and 30/50 keV. The number of modules, equipped with collimators, should be sufficient to achieve the required sensitivity to GRBs. The order of magnitude of the total detection area is 18000 cm2. The modules are slightly misaligned with each other tin order o achieve a wide FOV (> 1 sr).
b) a narrow field telescope (NFT), made of a broad-band Laue lens (50 – 600/700 keV) of a 20 m focal length, based on the exploitation of bent crystals, like those under development in Ferrara (FOV= 3.5 arcmin, angular resolution ≈20”). The NFT is coupled to a high efficiency (>80% above 600 keV) focal plane position sensitive detector, with 3D spatial resolution of at least 300 µm in the (X,Y) plane, fine spectroscopic response (1% @511 keV) and with polarization sensitivity.
With the WFM/S, we expect to accurately determine the energy spectrum of GRB prompt emission in the broadest band ever achieved with a single instrument, to measure the gamma-ray polarization of, at least, the brightest GRBs and to search for electromagnetic counterparts of Gravitational Wave events. In addition, with adequate scintillator bars and fast electronics, the Lorentz invariance for the brightest events can be tested. With the NFT, which is >~100 times more sensitive at a few hundred keV than any other past or planned mission, we can carry out for the first time a long-sought study of the afterglow spectrum of GRBs up to high energies (600/700 keV), including its polarization level. We can also establish, thanks to its high angular resolution (about 20”), whether the 511 keV positron annihilation line is due to the superposition of emission from point-like sources. In addition, we can address many Legacy Science topics mentioned in the Call, such as the origin of the high energy emission from magnetars, the first determination of the spectrum of blazars out to z~8 in between the two Synchrotron and Compton bumps, the determination of the sources that give rise to the gamma-ray diffuse background. For example, one could determine the high-energy cutoff from spectra of relatively bright AGN and study how this depends on the physics of the accretion (e.g. BH mass, Eddington ratio). We emphasize that the unprecedented sensitivity of the NFT and the combination with the WFM/S implies a large discovery space of this configuration. Moreover, such an instrument concept, thanks to the lightweight of the Laue lens and compactness of the wide field instrument, is expected to be within the limits imposed by an ESA Medium Size Mission.
The ASTENA mission, conceived within the AHEAD framework, consists of two coaligned instruments, a broad band Wide Field Monitor/Spectrometer WFM/S and a broad band Narrow Field Telescope (NFT). In the NFT a large geometric area Laue lens (3 m maximum diameter with a 20 m focal length) allows to focus the radiation of the 50 - 700 keV energy pass-band. Differently from other proposed Laue lenses in the past, the NFT is made of optimized thickness bent crystal tiles, made with Silicon (for the lower energy part of the lens pass-band) and Germanium (dedicated to the upper energy threshold). With these assumption we have optimized the NFT Field of View (FoV) to 3.5 arcmin with the angular resolution of 20”. The Laue lens is coupled with a high efficiency (>80% above 600 keV) focal plane position sensitive detector, with 3D spatial resolution of at least 300 µm in the (X,Y) plane and fine spectroscopic response (1% @511 keV) and with polarization sensitivity. In this SPIE contribution we will discuss the NFI geometry simulated with the MEGAlib toolkit and we will discuss its performances by simulating broad band and narrow energy typical sources, giving finally the instrument performances.
eXTP is a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism. Primary goals are the determination of the equation of state of matter at supra-nuclear density, the measurement of QED effects in highly magnetized star, and the study of accretion in the strong-field regime of gravity. Primary targets include isolated and binary neutron stars, strong magnetic field systems like magnetars, and stellar-mass and supermassive black holes. The mission carries a unique and unprecedented suite of state-of-the-art scientific instruments enabling for the first time ever the simultaneous spectral-timing-polarimetry studies of cosmic sources in the energy range from 0.5-30 keV (and beyond). Key elements of the payload are: the Spectroscopic Focusing Array (SFA) - a set of 11 X-ray optics for a total effective area of ∼0.9 m<sup>2</sup> and 0.6 m<sup>2</sup> at 2 keV and 6 keV respectively, equipped with Silicon Drift Detectors offering <180 eV spectral resolution; the Large Area Detector (LAD) - a deployable set of 640 Silicon Drift Detectors, for a total effective area of ∼3.4 m<sup>2</sup>, between 6 and 10 keV, and spectral resolution better than 250 eV; the Polarimetry Focusing Array (PFA) – a set of 2 X-ray telescope, for a total effective area of 250 cm<sup>2</sup> at 2 keV, equipped with imaging gas pixel photoelectric polarimeters; the Wide Field Monitor (WFM) - a set of 3 coded mask wide field units, equipped with position-sensitive Silicon Drift Detectors, each covering a 90 degrees x 90 degrees field of view. The eXTP international consortium includes major institutions of the Chinese Academy of Sciences and Universities in China, as well as major institutions in several European countries and the United States. The predecessor of eXTP, the XTP mission concept, has been selected and funded as one of the so-called background missions in the Strategic Priority Space Science Program of the Chinese Academy of Sciences since 2011. The strong European participation has significantly enhanced the scientific capabilities of eXTP. The planned launch date of the mission is earlier than 2025.
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, >8m<sup>2</sup> 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.
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 m<sup>2 </sup> 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 m<sup>2</sup>-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. <p> </p>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.
This paper summarizes the development of a successful project, LAUE, supported by the Italian Space Agency
(ASI) and devoted to the development of long foca length (up to 100—m) Laue lenses for hard X–/soft gamma–
ray astronomy (80-600 keV). The apparatus is ready and the assembling of a prototype lens petal is ongoing.
The great achievement of this project is the use of bent crystals. From measurements obtained on single crystals
and from simulations, we have estimated the expected Point Spread Function and thus the sensitivity of a lens
made of petals. The expected sensitivity is a few ×10<sup>−8</sup> photons cm<sup>−2</sup> s<sup>−1</sup> keV<sup>−1</sup>). We discuss a number of open astrophysical questions that can settled with such an instrument aboard a free-flying satellite.
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 m<sup>2</sup> 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 m<sup>2</sup>-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 m<sup>2</sup> (@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 m<sup>3</sup> 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.
We describe the analysis of BeppoSAX gamma-ray burst monitor on-ground calibrations performed after the full integration of the spacecraft in order to explore in detail the dependence of the detectors efficiency on the direction and energy of impinging photons. Analytical techniques have been used to determine with reasonable accuracy this function by fitting the angular response at different calibration energies with simple models partially derived from the underlying physics and partially semiempirical. Satisfactory results have been obtained for the two detectors which have almost clean field of view and are co-aligned with the wide field cameras. Work is still in progress for the others. Preliminary results of ground calibration analysis have been already used to derive spectral information on gamma-ray bursts impinging parallel to the axis of the two best performing shields.
The gamma ray burst monitor onboard the BeppoSAX satellite is a secondary function of the anticoincidence shields of the phoswich detection system hard x-ray experiment. For this reason the four CsI slabs operating as gamma ray bursts detectors have a not uniformly clear field of view. Actually the other SAX experiments partially obstruct the GRBM FOV in a way that strongly depends both on direction and energy. This peculiarity makes very hard to build-up a real response matrix of the experiment by simply interpolating the on-ground calibration. Therefore a complex activity of Monte Carlo simulation has been started using the MCNP code, in which the entire SAX satellite is described in a 3D geometrical reconstruction. This code is being used for the simulation of the on-ground calibration set-up, and once a good level of confidence is reached on that, it will be used to reconstruct direction, intensity and spectrum of the cosmic gamma ray bursts. In this paper we present the Monte Carlo set-up, discussing the approach to the work and the approximations that need to be done. Then the first results of the simulations are shown and compared, for some monochromatic energies and for several incoming directions, to the results obtained during the on-ground calibrations.
The Italian-Dutch satellite for x-ray astronomy BeppoSAX is successfully operating on a 600 km equatorial orbit since May 1996. We present here the in-flight performances of the gamma ray burst monitor experiment during its first year of operation. The GRBM is the secondary function of the four CsI(Na) slabs primarily operating as an active anticoincidence of the PDS hard x-ray experiment. It has a geometric area of about 400 cm<SUP>2</SUP> but, due to its location in the core of the satellite its effective area is dependent on the energy and direction of the impinging photons. A dedicated electronics allows to trigger on cosmic gamma-ray bursts. When the trigger condition is satisfied the light curve of the event is recorded from 8 s before to 98 s after the trigger time, with a maximum time resolution of 0.48 ms, in an energy band of 40 - 700 keV. As an instrument housekeeping the 1 s event ratemeter of the same detectors in the same energy band is stored regardless the trigger condition, allowing for an off- line detection of non-triggered events. Finally, the onboard software collects the event count rate that is used as anticoincidence, i.e. the events above a given energy threshold, typically kept at 100 keV. The flight-data screening is in progress, in order to extract real gamma ray bursts from the many sources of background. Already many results have been obtained, as those GRBs detected simultaneously with the wide field cameras oinboard BeppoSAX itself.
The phoswich detection system (PDS) is one of the four narrow field experiments on board the x-ray astronomy satellite BeppoSAX. PDS is devoted to deep temporal and spectral studies of celestial x-ray sources in the 15 - 300 keV energy band. It also includes a gamma-ray burst monitor. In this paper we compare the expected and observed in-flight performances. Our estimate of systematic errors in the background subtraction and in the spectral reconstruction are also presented and discussed.
The phoswich detection system (PDS) is one of the four narrow field experiments on board the SAX satellite. The PDS will be dedicated to deep temporal and spectral studies of celestial x- ray sources in the 15 - 300 keV energy band. It also includes a gamma-ray burst monitor. The PDS detector is composed of 4 actively shielded NaI(Tl)/CsI(Na) phoswich scintillators with a total geometric area of 795 cm<SUP>2</SUP> and a field of view of 1.3 degrees (FWHM). In this paper we report results of the experiment on-ground calibrations before its integration in the spacecraft and the expected experiment in-flight performance.