We describe the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X), a probeclass mission concept that will provide an unprecedented view of the X-ray sky, performing timing and spectroscopy over both a broad energy band (0.2–30 keV) and a wide range of timescales from microseconds to years. STROBE-X comprises two narrow-field instruments and a wide field monitor. The soft or low-energy band (0.2–12 keV) is covered by an array of lightweight optics (3-m focal length) that concentrate incident photons onto small solid-state detectors with CCD-level (85–175 eV) energy resolution, 100 ns time resolution, and low background rates. This technology has been fully developed for NICER and will be scaled up to take advantage of the longer focal length of STROBE-X. The higher-energy band (2–30 keV) is covered by large-area, collimated silicon drift detectors that were developed for the European LOFT mission concept. Each instrument will provide an order of magnitude improvement in effective area over its predecessor (NICER in the soft band and RXTE in the hard band). Finally, STROBE-X offers a sensitive wide-field monitor (WFM), both to act as a trigger for pointed observations of X-ray transients and also to provide high duty-cycle, high time-resolution, and high spectral-resolution monitoring of the variable X-ray sky. The WFM will boast approximately 20 times the sensitivity of the RXTE All-Sky Monitor, enabling multi-wavelength and multi-messenger investigations with a large instantaneous field of view. This mission concept will be presented to the 2020 Decadal Survey for consideration.
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.
Stellar explosions are relevant and interesting astrophysical phenomena. Since long ago we have been working on the characterization of novae and supernovae in X and gamma-rays, with the use of space missions. We have also been involved in feasibility studies of future instruments in the energy range from several keV up to a few MeV, in collaboration with other research institutes. High sensitivities are essential to perform detailed studies of cosmic explosions and cosmic accelerators, e.g., Supernovae and Classical Novae. In order to fulfil the combined requirement of high detection efficiency with good spatial and energy resolution, an initial module prototype based on CdTe pixel detectors is being developed. The detector dimensions are 12.5mm x 12.5mm x 2mm with a pixel pitch of 1mm x 1mm. Two kinds of CdTe pixel detectors with different contacts have been tested: ohmic and Schottky. Each pixel is bump bonded to a fanout board made of Sapphire substrate and routed to the corresponding input channel of the readout VATAGP7.1 ASIC, to measure pixel position and pulse height for each incident gamma-ray photon. The study is complemented by the simulation of the CdTe module performance using the GEANT 4 and MEGALIB tools, which will help us to optimise the detector design. We will report on the spectroscopy characterisation of the CdTe detector module as well as the study of charge sharing.
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 ESA M3 missions selected within the Cosmic Vision program in 2011 to carry out an assessment phase study and compete for a launch opportunity in 2022-2024. The phase-A studies of all M3 missions were completed at the end of 2013. LOFT is designed to carry on-board two instruments with sensitivity in the 2-50 keV range: a 10 m<sup>2</sup> class Large Area Detector (LAD) with a <1° collimated FoV and a wide field monitor (WFM) making use of coded masks and providing an instantaneous coverage of more than 1/3 of the sky. The prime goal of the WFM will be to detect transient sources to be observed by the LAD. However, thanks to its unique combination of a wide field of view (FoV) and energy resolution (better than 500 eV), the WFM will be also an excellent monitoring instrument to study the long term variability of many classes of X-ray sources. The WFM consists of 10 independent and identical coded mask cameras arranged in 5 pairs to provide the desired sky coverage. We provide here an overview of the instrument design, configuration, and capabilities of the LOFT WFM. The compact and modular design of the WFM could easily make the instrument concept adaptable for other missions.
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.
LOFT (Large Observatory For x-ray Timing) is one of the four missions selected in 2011 for assessment study for the
ESA M3 mission in the Cosmic Vision program, expected to be launched in 2024. The LOFT mission will carry two
instruments with their prime sensitivity in the 2-30 keV range: a 10 m<sup>2 </sup>class large area detector (LAD) with a <1°
collimated field of view and a wide field monitor (WFM) instrument based on the coded mask principle, providing
coverage of more than 1/3 of the sky. The LAD will provide an effective area ~20 times larger than any previous mission
and will by timing studies be able to address fundamental questions about strong gravity in the vicinity of black holes
and the equation of state of nuclear matter in neutron stars. The prime goal of the WFM will be to detect transient
sources to be observed by the LAD. However, with its wide field of view and good energy resolution of <300 eV, the
WFM will be an excellent monitoring instrument to study long term variability of many classes of X-ray sources. The
sensitivity of the WFM will be 2.1 mCrab in a one day observation, and 270 mCrab in 3s in observations of in the
crowded field of the Galactic Center. The high duty cycle of the instrument will make it an ideal detector of fast transient
phenomena, like X-ray bursters, soft gamma repeaters, terrestrial gamma flashes, and not least provide unique
capabilities in the study of gamma ray bursts. A dedicated burst alert system will enable the distribution to the
community of ~100 gamma ray burst positions per year with a ~1 arcmin location accuracy within 30 s of the burst. This
paper provides an overview of the design, configuration, and capabilities of the LOFT WFM instrument.
Today it is widely recognised that a measurement of the polarization status of cosmic sources high energy emission is a
key observational parameter to understand the active production mechanism and its geometry. Therefore new
instrumentation operating in the hard X/soft γ rays energy range should be optimized also for this type of measurement.
In this framework, we present the concept of a small high-performance spectrometer designed for polarimetry between
100 and 1000 keV suitable as a stratospheric balloon-borne payload dedicated to perform an accurate and reliable
measurement of the polarization status of the Crab pulsar, i.e. the polarization level and direction. The detector with 3D
spatial resolution is based on a CZT spectrometer in a highly segmented configuration designed to operate as a high
performance scattering polarimeter. We discuss different configurations based on recent development results and
possible improvements currently under study. Furthermore we describe a possible baseline design of the payload, which
can be also seen as a pathfinder for a high performance focal plane detector in new hard X and soft gamma ray focussing
telescopes and/or advanced Compton instruments. Finally we present preliminary data from Montecarlo undergoing
studies to determine the best trade-off between polarimetric performance and detector design complexity.
In the last few years we have been working on feasibility studies of future instruments in the gamma-ray range, from
several keV up to a few MeV. The innovative concept of focusing gamma-ray telescopes in this energy range, should
allow reaching unprecedented sensitivities and angular resolution, thanks to the decoupling of collecting area and
detector volume. High sensitivities are essential to perform detailed studies of cosmic explosions and cosmic
accelerators, e.g., Supernovae, Classical Novae, Supernova Remnants (SNRs), Gamma-Ray Bursts (GRBs), Pulsars,
Active Galactic Nuclei (AGN). In order to achieve the needed performance, a gamma-ray imaging detector with mm
spatial resolution and large enough efficiency is required.
In order to fulfill the combined requirement of high detection efficiency with good spatial and energy resolution, an
initial prototype of a gamma-ray imaging detector based on CdTe pixel detectors is being developed. It consists of a
stack of several layers of CdTe detectors with increasing thickness, in order to enhance the gamma-ray absorption in the
Compton regime. A CdTe module detector lies in a 11 x 11 pixel detector with a pixel pitch of 1mm attached to the
readout chip. Each pixel is bump bonded to a fan-out board made of alumina (Al<sub>2</sub>O<sub>3</sub>) substrate and routed to the
corresponding input channel of the readout ASIC to measure pixel position and pulse height for each incident gamma-ray
We will report the main features of the gamma-ray imaging detector performance such as the energy resolution for a set
of radiation sources at different operating temperatures.
Gamma-ray astrophysics in the MeV energy range plays an important role for the understanding of cosmic explosions
and acceleration mechanisms in a variety of galactic and extragalactic sources, e.g., Supernovae, Classical Novae,
Supernova Remnants (SNRs), Gamma-Ray Bursts (GRBs), Pulsars, Active Galactic Nuclei (AGN).
Through the development of focusing telescopes in the MeV energy range, it will be possible to reach unprecedented
sensitivities, compared with those of the currently operating gamma ray telescopes. In order to achieve the needed
performance, a detector with mm spatial resolution and very high peak efficiency is required. It will be also desirable
that the detector could detect polarization of the source.
Our research and development activities in Barcelona aim to study a gamma-ray imaging spectrometer in the MeV range
suited for the focal plane of a gamma-ray telescope mission, based on CdTe pixel detectors arranged in multiple layers
with increasing thicknesses, to enhance gamma-ray absorption in the Compton regime. We have developed an initial
prototype based on several CdTe module detectors, with 11x11 pixels, a pixel pitch of 1mm and a thickness of 2mm.
Each pixel is stud-bump bonded to a fanout board and routed to a readout ASIC to measure pixel position, pulse height
and rise time information for each incident gamma-ray photon.
We will report on the results of an optimization study based on simulations, to select the optimal thickness of each CdTe
detector within the module to get the best energy resolution of the spectrometer.