Arcade 2 measurement of the absolute sky brightness at 3-90GHz

Abstract

The ARCADE 2 instrument has measured the absolute temperature of the sky at frequencies 3, 8, 10, 30, and 90GHz, using an open-aperture cryogenic instrument observing at balloon altitudes with no emissive windows between the beam-forming optics and the sky. An external blackbody calibrator provides an in situ reference. Systematic errors were greatly reduced by using differential radiometers and cooling all critical components to physical temperatures approximating the cosmic microwave background (CMB) temperature. A linear model is used to compare the output of each radiometer to a set of thermometers on the instrument. Small corrections are made for the residual emission from the flight train, balloon, atmosphere, and foreground Galactic emission. The ARCADE 2 data alone show an excess radio rise of 54 ± 6mK at 3.3GHz in addition to a CMB temperature of 2.731 ± 0.004K. Combining the ARCADE2 data with data from the literature shows an excess power-law spectrum of T = 24.1 ± 2.1 (K) (ν/ν0)-2.599 ± 0.036 from 22 MHz to 10GHz (ν0 = 310 MHz) in addition to a CMB temperature of 2.725 ± 0.001K. © 2011. The American Astronomical Society. All rights reserved.