WMAP DR1 Beam Maps Description

The data made available through this page has been updated. The most recent version of this data may be accessed through https://lambda.gsfc.nasa.gov/product/wmap/current/

The main and near-sidelobe response of each of the 20 WMAP antenna feeds has been mapped in-flight using observations of Jupiter. These maps are constructed from calibrated time-ordered observations in which Jupiter passed within 5 degrees of either the A- or B-side WMAP optic axis, comprising data from Oct/Nov 2001 and Feb/Mar 2002. The time-ordered observations are corrected to a fiducial Jupiter distance of 5.2 AU, background subtracted and corrected for aberration. For purposes of constructing beam maps, the observations are assigned to 2.4 arcminute bins on a coordinate grid centered on either the A or B-side focal plane axis. The beam response for each feed is computed from the average temperature in each bin. No correction has been made for the side-A vs. side-B input transmission imbalance.

Beam maps are provided in 10 FITS image format files, one file for each differencing assembly. Each file contains:

• the beam map for the A side, in mK (antenna temperature)
• the statistical error of each bin of the A side beam map, in mK (antenna temperature). The statistical error is based on the number of observations in each bin.
• the beam map for the B side, in mK (antenna temperature)
• the statistical error of each pixel of the B side beam map, in mK (antenna temperature)

The beam coordinates form an equal area rectangular coordinate system centered on the optic axis of the spacecraft. They are related to coordinates theta (elevation from optic axis) and phi (azimuth about optic axis) as follows:

• X_beam = 2*sin(theta/2) * cos(phi)
• Y_beam = 2*sin(theta/2) * sin(phi)

More details can be found in:

"First Year Wilkinson Microwave Anisotropy Probe (WMAP) Results:
Beam Profiles and Window Functions", Page, et al., 2003

WMAP Explanatory Supplement