The primary scientific mission of the Black Hole Finder Probe (BHFP), part of the NASA Beyond Einstein program, is to survey the local Universe for black holes over a wide range of mass and accretion rate. One approach to such a survey is a hard X-ray coded-aperture imaging mission operating in the 10-600 keV energy band, a spectral range that is considered to be especially useful in the detection of black hole sources. The development of new inorganic scintillator materials provides improved performance (for example, with regards to energy resolution and timing) that is well suited to the BHFP science requirements. Detection planes formed with these materials coupled with a new generation of readout devices represent a major advancement in the performance capabilities of scintillator-based gamma cameras. Here, we discuss the Coded Aperture Survey Telescope for Energetic Radiation (CASTER), a concept that represents a BHFP based on the use of the latest scintillator technology.
Swift is a first-of-its-kind multiwavelength transient observatory for
gamma-ray burst astronomy. It has the optimum capabilities for the
next breakthroughs in determining the origin of gamma-ray bursts and
their afterglows, as well as for using bursts to probe the early Universe. Swift will also monitor the soft gamma repeaters and perform the first sensitive hard X-ray survey of the sky. The mission is being developed by an international collaboration and consists of three instruments, the Burst Alert Telescope (BAT), the X-ray Telescope (XRT), and the Ultraviolet and Optical Telescope (UVOT). The BAT, a wide-field gamma-ray detector, will detect >100
gamma-ray bursts per year with a sensitivity 5 times that of BATSE.
The sensitive narrow-field XRT and UVOT will be autonomously slewed to
the burst location within 20 to 70 seconds to determine 0.3-5.0 arcsec
positions and perform optical, UV, and X-ray spectrophotometry.
Strong education/public outreach and follow-up programs will help to
engage the public and the astronomical community. Swift launch is
planned for September 2003.
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
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.
New, high spatial resolution CdZnTe (CZT) and silicon (Si) pixel detectors are highly suitable for x-ray astronomy. These detectors are planned for use in wide field of view, imaging x-ray, and low energy gamma-ray all-sky monitor (AXGAM) in a future space mission. The high stopping power of CZT detectors combined with low-noise front-end readout makes possible an order of magnitude improvement in spatial and energy resolution in x-ray detection. The AXGAM instrument will be built in the form of a fine coded aperture placed over two-dimensional, high spatial resolution and low energy threshold CZT pixel detector array. The preliminary result of CZT and silicon pixel detector test with low-noise readout electronics system are presented. These detectors may also be used with or without modification for medical and industrial imaging.
The on-board flight software for the Near Earth Asteroid Rendezvous (NEAR) spacecraft was modified to produce continuous 1-sec sampled rate information from the shield of the x-ray and gamma ray spectrometer (XGRS) instrument. Since the XGRS shield can also detect gamma ray bursts (GRB), this rate information can be used in combination with the GRB detections by the Ulysses and near-Earth GRB instruments as part of the interplanetary network (IPN) to triangulate the source direction of GRBs. It is the long baseline of NEAR combined with the Ulysses baseline that makes small error box locations possible. We have developed an automated system to analyze the periodic telemetry dumps from the NEAR spacecraft. It extracts this new data type, scans the ate information for increases which are plausibly of GRB origin, and combines these with the GRB detections from the others spacecraft. Because the processing is automated, the time delay to produce the triangulated positions is kept to a minimum, up to 48 hours. This automated processing and distribution of the GRB locations is done within the GRB Coordinates Network system. About 60 locations per year with errors ranging from a few to tens of arcminutes are expected. These rapid precise localizations may provide about 10 times the rate currently provided by the WFC and NFI instruments on BeppoSAX.
We propose a new astrophysics space mission for a low energy gamma-ray-burst observatory (LEGO) that will fit the envelope of a small-explorer (SMEX) type mission. The LEGO instrument combines silicon pixel detectors with ultra-high energy resolution and a novel cost effective fine-pitch coded mask, to image the sky with sub-arcminute accuracy in the 0.3 - 30 keV range with a wide field-of-view. LEGO is well adapted to study hundreds of short transients such as gamma-ray bursts and soft gamma repeaters in the unexplored energy range below 5 keV. LEGO takes one of the next logical steps in GRB studies in the post-BeppoSAX era by attacking the astrophysics questions raised by recent discoveries of variable radio, optical, and x-ray counterparts to burst sources. In addition to monitoring the sky for gamma-ray bursts, LEGO would provide a first all-sky monitor in the 0.3 - 30 keV range. LEGO will be sensitive to all mCrab sources in the sky in a day and to 0.1 mCrab sources in a year, and thus, may provide daily light curves and sensitive spectral measurements on about 103 objects and yearly data on an order of magnitude more sources.
A wide field-of-view, arcsecond imaging, high energy resolution x-ray and low energy gamma ray detector is proposed for a future space mission. It is specifically designed to monitor and study gamma ray bursts (GRBs) with high energy and angular resolution and also find counterparts at other wavelengths. Detection of GRBs requires wide field-of-view ((pi) to 2 (pi) field-of-view) and high sensitivity. This is achieved by using high quantum efficiency CdZnTe pixel detectors with a low energy threshold (few keV) to observe the larger flux levels at lower energies, and large effective area (625 to 1,000 cm2) per coded aperture imaging module. Counterpart searches can only be done with ultra high angular resolution detectors (10 to 30 arcsecond FWHM) which gives 1 to 5 arcsecond position determination especially for strong GRBs. A few arcsecond size error box is expected to contain at most one object observed at another wavelength. This will be achieved by using ultra high spatial resolution pixel detectors (100 by 100 microns) and a similar resolution coded aperture to achieve the required angular resolution. AXGAM also has two other important advantages over similar detectors: (1) excellent low energy response (greater than 1 keV) and (2) high energy resolution (less than 6% at 5.9 keV, less than 3% at 14 keV, less than 4% at 122 keV). The low energy range may provide important new information on GRBs and the high energy resolution is expected to help in the observation and identification of emission and absorption lines in the GRB spectrum. The effective energy range is planned to be 2 to 200 keV which is exceptionally wide for such a detector. AXGAM will be built in the form of a 'bucky ball' using a coded aperture mask in a semi-geodesic dome arrangement placed over a two-dimensional, high resolution CdZnTe pixel detector array using newly developed p-i-n detector technology. The p-i-n structure decreases the electron and hole trapping effect and increases energy resolution significantly. The major scientific goals of the proposed mission in addition to continuously monitoring gamma- ray bursts, is to observe AGNs, transient phenomena, isolated and binary pulsars, and solar flares. A space deployed AXGAM detector is expected to observe several hundred gamma ray bursts per year.
We are studying a gamma-ray burst mission concept called burst arcsecond imaging and spectroscopy (BASIS) as part of NASA's new mission concepts for astrophysics program. The scientific objectives are to accurately locate bursts, determine their distance scale, and measure the physical characteristics of the emission region. Arcsecond burst positions (angular resolution approximately 30 arcsec, source positions approximately 3 arcsec) will be obtained for approximately 100 bursts per year using the 10 - 100 keV emission. This will allow the first deep, unconfused counterpart searches at other wavelengths. The key technological breakthrough that makes such measurements possible is the development of CdZnTe room-temperature semiconductor detectors with fine (approximately 100 micron) spatial resolution. Fine spectroscopy will be obtained between 0.2 and 150 keV. The 0.2 keV threshold will allow the first measurements of absorption in our galaxy and possible host galaxies, constraining the distance scale and host environment.
We have proposed a gamma-ray burst mission concept called burst arcsecond imaging and spectroscopy (BASIS) in response to NASA's announcement for new mission concept studies. The scientific objectives are to accurately locate bursts, determine their distance scale, and measure the physical characteristics of the emission region. Arcsecond burst positions (angular resolution approximately 30 arcsec, source positions approximately 3 arcsec for greater than 10-6 erg cm-2 bursts) are obtained for about 100 bursts per year using the 10 - 200 keV emission. This allows the first deep, unconfused counterpart searches at other wavelengths. The key technological breakthrough that makes such measurements possible is the development of CdZnTe room-temperature semiconductor detectors with fine (approximately 100 micron) spatial resolution. Fine spectroscopy is obtained between 0.2 keV and 200 keV. The 0.2 keV threshold allows the first measurements of absorption in our galaxy and possible host galaxies, constraining the distance scale and host environment. The mission concept and its scientific objectives are described.
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.