The INTEGRAL X-ray monitor, JEM-X, (together with the two gamma ray instruments, SPI and IBIS) provides simultaneous imaging with arcminute angular resolution in the 3-35 keV band. The good angular resolution and low energy response of JEM-X plays an important role in the detection and identification of gamma ray sources as well as in the analysis and scientific interpretation of the combined X-ray and gamma ray data. JEM-X is a coded aperture X-ray telescope consisting of two identical detectors. Each detector has a sensitive area of 500 cm<sup>2</sup>, and views the sky through its own coded aperture mask. The coded masks are located 3.4 m above the detector windows. The detector field of view is constrained by X-ray collimators (6.6° FOV, FWHM).
The TopHat instrument was designed to operate on the top of a high altitude balloon. From this location, the experiment could efficiently observe using a clean beam with extremely low contamination from the far side lobes of the instrument beam. The experiment was designed to scan a large portion of the sky directly above it and to map the anisotropy of the Cosmic Microwave Background (CMB) and thermal emission from galactic dust. The instrument used a one-meter class telescope with a five-band single pixel radiometer spanning the frequency range from 150-600 GHz. The radiometer used bolometric detectors operating at ~250mK. Here, we report on the flight of the TopHat experiment over Antarctica in January, 2001 and describe the scientific goals, the operation, and in-flight performance.
We describe the engineering design and operational concept for a series of three complementary top mounted balloon- borne experiments to measure the Cosmic Microwave Background Radiation anisotropy, culminating in a two week circumpolar flight from McMurdo Station, Antarctica. Each experiment is designed to provide a maximum science return in addition to acting as a pathfinder to the successor flights of top- mounted balloon-borne experiments. The experiment program, named TopHat, will involve the launch and operation of the first far-infrared and microwave telescope flown entirely from the top of a 28 million cubic foot balloon. It utilizes a two axis gimbal pointing system, a one meter Cassegrain optical system with a chopping secondary mirror, and a <SUP>3</SUP>He evaporation cryostat designed to maintain a bolometer detector temperature of 0.25 K for 30 days without cycling. The series of flights will begin with an engineering test flight scheduled for launch in July 1996 from Palestine, Texas, followed by a pointing experiment to be flown from Ft. Sumner, New Mexico in April 1997. A spinning experiment will be launched from Ft. Sumner in April 1998 and Antarctica in December 1998.