All-sky X-ray and gamma-ray monitor (AXGAM)

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 detect and find counterparts at other wavelengths for gamma ray bursts (GRBs). Detection of GRBs require wide field-of-view (π to 2π field-of-view) and high sensitivity. This will be achieved by using high quantum efficiency CdZnTe pixel detectors, low energy threshold (few keV) to observe larger flux levels that may be possible 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 (10 to 30 arcsecond FWHM) which gives 1 to 5 arcsecond position determination especially for strong GRBs. A few arcsecond resolution error box is expected to contain only one counterpart observed at another wavelength. This will be achieved by using ultra high spatial resolution pixel detectors (50×50 to 100×100 micron) 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 (>1 keV) and (2) high energy resolution (<6%@5.9 keV, <3%@14 keV, <4%@122 keV). The low energy range may provide important new information on their cause 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. AXCAM will be built in the form of a “Bucky Ball” using a coded aperture mask in a semi geodesic dome arrangement placed over a 2D 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 AGN, 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