Scanning Beams

LFI beams

Maps are released of the Stokes parameters of the band-averaged scanning beams. The averages are performed using the RIMO bandpass, assuming a flat spectrum of the incoming radiation. The Stokes parameter maps contain the complete information about the field intensity and polarization properties. The Main Beam, Intermediate Beam, and Sidelobes are released separately.

More information on LFI beams can be found in Planck-2015-A04 and on HFI beams in Planck-2015-A07

File Names

The file names are of the form

LFI_ScanBeam-{mb,ib,sl}_{fff}-{rrr}_R2.{nn}.stokes,

where:

• fff denotes the frequency;
• mb denotes the Main Beams;
• ib denotes the Intermediate Beam;
• sl denotes the Sidelobes;
• rrr denotes the radiometer;
• R2.nn is the version.

At the present time, HFI is not releasing the Scanning Beams.

FITS file structure

The FITS files contain a primary extension with no data and a minimal header, as well as one BINTABLE extension with data and with a description of the data in the header keywords. The BINTABLE extension consist of four columns, each containing the array of one Stokes parameter. The columns are:

• "Beamdata", containing I;
• "BeamdataQ", containing Q;
• "BeamdataU", containing U;
• "BeamdataV", containing V.

The Main Beam, Intermediate Beams, and Sidelobes are saved with a different data format, as described below.

• Main Beams are projected onto the tangent plane to the sphere, and sampled on a grid. The grid includes an angular region expressed by the keyword "angularCut", and its dimensions are given by the keywords "Nx" and "Ny", representing the number of columns and rows. Each column of the BINDATA extension contains a sequence of the N_x× N_y samples of the map in row major order. The keywords "Xcentre" and "Ycentre" express the coordinates of the beam maximum (i.e., where the sphere intersects the tangent plane).

Main Beam file structure

Column Name	Data Type	Units	Description	Comment
BEAMDATA	Real*4	None	Stokes parameter I<\i>
BEAMDATAQ	Real*4	None	Stokes parameter Q<\i>
BEAMDATAU	Real*4	None	Stokes parameter U<\i>
BEAMDATAV	Real*4	None	Stokes parameter V<\i>
Keyword	Data Type	Value	Description	Comment
Nx	Int	601	Number of x-axis samples	x axis aligned with the direction of the "S" arm
Ny	Int	601	Number of y-axis samples	y axis aligned with the direction of the "M" arm
Xcentre	Int	301	x coordinate of the beam centre
Ycentre	Int	301	y coordinate of the beam centre
Xdelta	Float		x step in radians
Ydelta	Float		y step in radians

• Intermediate Beams and Sidelobes are sampled on the sphere. The resolution in θ and φ are given by the keywords "Ntheta" and "Nphi". The columns of the BINDATA extension contain the sequence of Nphi Stokes parameters for each θ.

Intermediate Beam and Sidelobes file structure

Column Name	Data Type	Units	Description	Comment
BEAMDATA	Real*4	None	Stokes parameter I<\i>
BEAMDATAQ	Real*4	None	Stokes parameter Q<\i>
BEAMDATAU	Real*4	None	Stokes parameter U<\i>
BEAMDATAV	Real*4	None	Stokes parameter V<\i>
Keyword	Data Type	Value	Description	Comment
Ntheta	Int		Number of θ samples	Colatitude
Nphi	Int		Number of φ samples	Longitude
Mintheta	Float		Minimum value of θ
Maxtheta	Float		Maximum value of θ
angularCut	Float		Angular cut [deg]

HFI Beams

The HFI scanning beams are a combination of observations of Saturn, for the central parts, and Jupiter, for the wings, as described in the Beams section of this document, and in Section 4.1 of Planck-2015-A07 on Hybrid beams. Saturn data are used where they are signal-dominated; when the SNR of Saturn drops to < 9, Jupiter data are used, after binning them azimuthally. Beyond that, i.e., below the noise floor of the Jupiter data, and out to 100 arcmin, a power law (~θ ^-3) is used, where the exponent is derived from GRASP physical optics models. The figure below, taken from the Beams section of this document, shows graphically the different portions of the beam model.

Scanning beam map for detector 143-6 showing a rough diagram of the regions that are handled with a different data selection or binning.

The beams are provided in FITS files named

• HFI_ScanBeam_{det-name}_R2.nn.fits,

where det-name is of the form 100-1a, and nn is the version number. Each file contains a single IMAGE extension. The image is 6001x6001 pixels of size 2x2 arcsec² (given in the DELTAX and DELTAY keywords), centred on pixel 3001,3001, and normalised to 1 at the maximum, where X and Y and in the Dxx reference system.