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18 October 1996 Burst locations with an arc second telescope (BLAST)
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Abstract
Burst locations with an arc second telescope (BLAST) is a new mission concept being studied for NASA's medium explorer (MIDEX) mission opportunities. The principal scientific objectives of the BLAST mission are (1) to localize gamma- ray burst (GRB) positions to arcsec accuracy; (2) to search for enhancements in the rate of GRBs toward M31; and (3) to conduct the most sensitive sky survey to date of x-ray sources in the 7 - 200 keV regime. These objectives are achieved using a large array of position-sensitive scintillation detectors with a total area of 17,000 cm2. This array is combined with a large field of view telescope (greater than 1 steradian) comprising two separate imaging systems. A coded aperture telescope provides arcminute source localization. For low energy x-rays (less than 50 keV), the aperture is also defined by phase modulation grids with provide complementary arcsecond information. The grid system consists of two aperture planes with 'checker board' patterns of slightly different pitch. The beating between the two grid pitches casts a broad interference pattern on the detector plane. Determining the phase of this interference pattern in both coordinates gives the location of a point source source in the sky, with aliased positions at approximately 1 arcmin spacing. The arcmin ambiguity is resolved by the coded aperture image. BLAST has a sensitivity to bursts of 0.03 photons cm-2 s-1, almost ten times more sensitive than BATSE. We expect to position 20 bursts per year to better than 2 arcsec accuracy and 35 bursts per year to better than 5 arcsec. BLAST will provide an all sky survey in hard x-rays with a sensitivity of 0.2 milliCrab at low energies.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
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