The MSAM/TopHat program for measuring the CMBR anisotropy

Abstract

We describe a series of three complementary balloon-borne measurements of the anisotropy in the Cosmic Microwave Background Radiation (CMBR) and astrophysical foreground sources on angular scales from 0.5° to 180° at frequencies between 70 and 700 GHz. On the largest angular scales, we plan to finish mapping the entire sky in the far-infrared with 3.8° resolution and sensitivity comparable to the COBE/DMR first year maps. The analysis of the first flight of this Far-Infrared Survey (FIRS) led to the confirmation of the LOBE anisotropy discovery. On the 0.5° to 3° angular scale we will refine our pointing telescope and make an additional flight of the Medium-Scale Anisotropy Measurement (MSAM) using the existing radiometer. This will strengthen the results obtained from the first flight (Cheng et al. 1993a). Two subsequent flights, observing the same sky positions with a lower frequency multi-channel radiometer (MSAM 11), will ensure that the result is not contaminated by Galactic or extragalactic foreground radiation. Concurrent with the above program, we will implement a new concept in CMBR measurements which will provide the next step in observational capabilities. This experiment, named TopHat, will be mounted on top of a balloon and will observe for two weeks in a circumpolar flight launched from McMurdo Station, Antarctica. By providing a combination of reduced systematics and extended integration time, it offers a factor of 30 improvement in sensitivity to CMBR anisotropy over existing measurements.