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.
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 balloon-borne Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument will provide a near-optimal
combination of high-resolution imaging, spectroscopy, and polarimetry of solar-flare gamma-ray/hard X-ray emissions
from ~20 keV to >~10 MeV. GRIPS will address questions raised by recent solar flare observations regarding particle
acceleration and energy release, such as: What causes the spatial separation between energetic electrons producing hard
X-rays and energetic ions producing gamma-ray lines? How anisotropic are the relativistic electrons, and why can they
dominate in the corona? How do the compositions of accelerated and ambient material vary with space and time, and
why? The spectrometer/polarimeter consists of sixteen 3D position-sensitive germanium detectors (3D-GeDs), where
each energy deposition is individually recorded with an energy resolution of a few keV FWHM and a spatial resolution
of <0.1 mm3. Imaging is accomplished by a single multi-pitch rotating modulator (MPRM), a 2.5-cm thick tungstenalloy
slit/slat grid with pitches that range quasi-continuously from 1 to 13 mm. The MPRM is situated 8 meters from the
spectrometer to provide excellent image quality and unparalleled angular resolution at gamma-ray energies (12.5 arcsec
FWHM), sufficient to separate 2.2 MeV footpoint sources for almost all flares. Polarimetry is accomplished by
analyzing the anisotropy of reconstructed Compton scattering in the 3D-GeDs (i.e., as an active scatterer), with an
estimated minimum detectable polarization of a few percent at 150–650 keV in an X-class flare. GRIPS is scheduled for
a continental-US engineering test flight in fall 2013, followed by long or ultra-long duration balloon flights in
The Nuclear Compton Telescope (NCT) is a balloon-borne soft
gamma-ray (0.2MeV-10MeV) telescope designed to study astrophysical
sources of nuclear line emission and polarization. A prototype
instrument was successfully launched from Ft. Sumner, NM on June 1,
2005. The NCT prototype consists of two 3D position sensitive
High-Purity-Germanium (HPGe) strip detectors fabricated with
amorphous Ge contacts. The novel ultra-compact design and new
technologies allow NCT to achieve high efficiencies with excellent
spectral resolution and background reduction. Energy and positioning calibration data was acquired pre-flight in Fort Sumner, NM after the full instrument integration. Here we discuss our calibration techniques and results, and detector efficiencies. Comparisons with simulations are presented as well.
The Advanced Compton Telescope (ACT), the next major step in gamma-ray astronomy, will probe the fires where
chemical elements are formed by enabling high-resolution spectroscopy of nuclear emission from supernova explosions.
During the past two years, our collaboration has been undertaking a NASA mission concept study for ACT. This study
was designed to (1) transform the key scientific objectives into specific instrument requirements, (2) to identify the most
promising technologies to meet those requirements, and (3) to design a viable mission concept for this instrument. We
present the results of this study, including scientific goals and expected performance, mission design, and technology
We flew a prototype of the Nuclear Compton Telescope (NCT) on a high altitude balloon from Fort Sumner, New Mexico on 2005 June 1. The NCT prototype is a soft gamma-ray (0.2-15 MeV) telescope designed to study, through spectroscopy, imaging, and timing, astrophysical sources of nuclear line emission and gamma-ray polarization. Our program is designed to develop and test the technologies and analysis techniques crucial for the Advanced Compton Telescope satellite, while studying gamma-ray radiation with very high spectral resolution, moderate angular resolution, and high sensitivity. The NCT prototype utilizes two, 3D imaging germanium detectors (GeDs) in a novel, ultra-compact design optimized for nuclear line emission (0.5-2 MeV) and polarization in the 0.2-0.5 MeV range. Our prototype flight was a critical test of the novel instrument technologies, analysis techniques, and background rejection procedures we have developed for high resolution Compton telescopes.
The primary scientific objective of RHESSI Small Explorer mission is to investigate the physics of particle acceleration and energy release in solar flares, through imaging and spectroscopy of X-ray/gamma-ray continuum and gamma-ray lines emitted by accelerated electrons and ions, respectively. RHESSI utilizes rotating modulator collimators together with cooled germanium detectors to image X-rays/gamma-rays from 3 keV to 17 MeV. It provides the first hard X-ray imaging spectroscopy, the first high resolution spectroscopy of solar gamma-ray liens, and the first imaging of solar gamma-ray lines and continuum. Here we briefly describe the mission and instrumentation, and illustrate its capabilities with solar and cosmic observations obtained in the first 17 months of operation.
We are developing a 2-detector high resolution Compton telescope utilizing 3D imaging germanium detectors (GeDs) to be flown as a balloon payload in Spring 2004. This instrument is a prototype for the larger Nuclear Compton Telescope (NCT), which utilizes 12-GeDs. NCT is a balloon-borne soft γ-ray (0.2-15 MeV) telescope designed to study, through spectroscopy, imaging, and timing, astrophysical sources of nuclear line emission and γ-ray polarization. The NCT program is designed to develop and test the technologies and analysis techniques crucial for the Advanced Compton Telescope, while studying γ-ray radiation with very high spectral resolution, moderate angular resolution, and high sensitivity. NCT has a novel, ultra-compact design optimized for studying nuclear line emission in the critical 0.5-2 MeV range, and polarization in the 0.2-0.5 MeV range. The prototype flight will critically test the novel instrument technologies, analysis techniques, and background rejection procedures we have developed for high resolution Compton telescopes. In this paper we present the design and preliminary results of laboratory performance tests of the NCT flight electronics.
Our collaboration is developing a 2-detector prototype high resolution Compton telescope utilizing 3D imaging germanium detectors (GeDs) for a test balloon flight in Spring 2003. This instrument is a prototype for a full 12-GeD instrument, the Nuclear Compton Telescope. NCT is a balloon-borne soft gamma-ray (0.2-15 MeV) telescope designed to study astrophysical sources of nuclear
line emission and polarization. The NCT program is designed to develop and test the technologies and analysis techniques crucial for the Advanced Compton Telescope, while studying gamma-ray radiation with very high spectral resolution, moderate angular resolution, and high sensitivity. NCT has a novel, ultra-compact design optimized for studying nuclear line emission in the critical 0.5-2 MeV range, and polarization in the 0.2-0.5 MeV range. This prototype flight will critically test the novel instrument technologies, analysis techniques, and background rejection procedures we have developed for high resolution Compton telescopes. We present the design and expected performance of this prototype NCT instrument.
B-MINE is a concept for a balloon mission designed to probe the
deepest regions of a supernova explosion by detecting <sup>44</sup>Ti emission at 68 keV with spatial and spectral resolutions that are sufficient to determine the extent and velocity distribution of the <sup>44</sup>Ti emitting region. The payload introduces the concept of focusing optics and microcalorimeter spectroscopy to nuclear line emission astrophysics. B-MINE has a thin, plastic foil telescope multilayered to maximize the reflectivity in a 20 keV band centered at 68 keV and a microcalorimeter array optimized for the same energy band. This combination provides a reduced background, an energy resolution of 50 eV and a 3F sensitivity in 10<sup>6</sup> s of 3.3 10<sup>-7</sup> ph cm<sup>-2</sup> s<sup>-1</sup> at 68 keV.
During the course of a long duration balloon flight, B-MINE could
carry out a detailed study of the 44Ti emission line centroid and
width in CAS A.
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a
NASA Small Explorer satellite designed to study hard x-ray and
gamma-ray emission from solar flares. In addition, its
high-resolution array of germanium detectors can see photons
from high-energy sources throughout the Universe. Here we discuss
the various algorithms necessary to extract spectra, lightcurves,
and other information about cosmic gamma-ray bursts, pulsars,
and other astrophysical phenomena using an unpointed, spinning
array of detectors. We show some preliminary results and discuss
our plans for future analyses. All RHESSI data are public, and
scientists interested in participating should contact the
Although designed primarily as a hard X-ray imager and spectrometer, the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is also capable of measuring the polarization of hard X-rays (20-100 keV) from solar flares. This capability arises from the inclusion of a small unobstructed Be scattering element that is strategically located within the cryostat that houses the array of nine germanium detectors. The Ge detectors are segmented, with both a front and rear active volume. Low energy photons (below about 100 keV) can reach a rear segment of a Ge detector only indirectly, by scattering. Low energy photons from the Sun have a direct path to the Be and have a high probability of Compton scattering into a rear segment of a Ge detector. The azimuthal distribution of these scattered photons carries with it a signature of the linear polarization of the incident flux. Sensitivity estimates, based on simulations and in-flight background measurements, indicate that a 20-100 keV polarization sensitivity of less than a few percent can be achieved for X-class flares.
In response to the recent NASA-SMEX Announcement of Opportunity, our collaboration proposed Cyclone, the Cyclotron/Nuclear Explorer. Cyclone is a broadband pointed astrophysical observatory, combining the highest spectral resolutions (E/(Delta) E approximately 30 - 300) and angular resolutions (15') achieved in the optimized hard X-ray range (10 - 200 keV). The instrument consists of 19 co-aligned rotation modulation collimator (RMC) telescopes, each with a high spectral resolution, 6-cm diameter germanium detector (GeD) covering energies from 3 keV to 600 keV. Both the optics and detectors are actively shielded with 15-mm BGO to gain low background an high sensitivity to astrophysical sources. A 550-km altitude, circular equatorial orbit also minimizes background. Building strongly upon instrumental heritage from the High-Energy Solar Spectroscopic Imager (HESSI) program, Cyclone would be ready for launch by September 2003. The instrument design and expected performance are discussed, as well as a brief overview of scientific goals.
The primary scientific objective of the High Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission selected by NASA is to investigate the physics of particle acceleration and energy release in solar flares. Observations will be made of x-rays and (gamma) rays from approximately 3 keV to approximately 20 MeV with an unprecedented combination of high resolution imaging and spectroscopy. The HESSI instrument utilizes Fourier- transform imaging with 9 bi-grid rotating modulation collimators and cooled germanium detectors. The instrument is mounted on a Sun-pointed spin-stabilized spacecraft and placed into a 600 km-altitude, 38 degrees inclination orbit.It will provide the first imaging spectroscopy in hard x-rays, with approximately 2 arcsecond angular resolution, time resolution down to tens of ms, and approximately 1 keV energy resolution; the first solar (gamma) ray line spectroscopy with approximately 1-5 keV energy resolution; and the first solar (gamma) -ray line and continuum imaging,with approximately 36-arcsecond angular resolution. HESSI is planned for launch in July 2000, in time to detect the thousands of flares expected during the next solar maximum.
The elements of a high resolution gamma-ray spectrometer, developed for observations of solar flares, are described. Emphasis is given to those aspects of the system that relate to its operation on a long duration balloon platform. The performance of the system observed in its first flight, launched from McMurdo Station, Antarctica on 10 January, 1992, is discussed. Background characteristics of the antarctic balloon environment are compared with those observed in conventional mid-latitude balloon flights and the general advantages of long duration ballooning are discussed.