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ACTPol

Product Name
Beams 2016
Mission
ACT

Description

Beams

These files represent the beam transforms (Fourier space) and radial profiles (real space) for use with the ACTPol two-season data. The beams are described in Louis et al. 2016.
The real space beam is the azimuthally averaged point spread function, normalized to 1 at theta=0, including the effects of pointing variance and the pixel aperture. The beam is fit by 1/r^3 in a range of 3 to 5 arcminutes. The format of the real space radial profile is:

  • Column 1: radius, in degrees
  • Column 2: beam profile, normalized to 1 at radius = 0

The beam transform is the harmonic transform (on the sphere) of the azimuthally averaged beam. The Fourier space window functions is obtained by squaring the beam transform. The calibration pivot is at ell = 1400. The format of the ell-space beam transforms is:

  • Column 1: ell
  • Column 2: B_ell
  • Columns 3,4,...: dB1_ell, dB2_ell, ...

B_ell is the harmonic transform of the real space beam, assumed to be azimuthally symmetric. The angular power spectrum "window function" due to the instrument point spread function is proportional to the square of B_ell.
Each dB#_ell is an independent mode of the uncertainty in B_ell. To average a result over the ensemble of beam realizations, generate trial beams

  • B' = B + a1 * dB1 + a2 * dB2 + ...

where (a1, a2, ...) are drawn from the normal distribution with mean 0 and variance 1.
The normalization ell and error mode pivot ell can be found in the comments of each beam_tform file.
The pointing variance is included in the following way:
The variation in pointing for each array and field is estimated using per-TOD pointing corrections and then the noise-weighted mean and variance in pointing is then applied to the instantaneous beams. An additional correction is applied by fitting the instantaneous beam to bright sources (after subtracting the estimated local pointing variance) in combined field maps.
The beam files include RJ->CMB spectral corrections for use with CMB. These are referenced by the suffix, e.g.

beam_tform_160201___.txt -- ell-space beam transform
beam_profile_160201___.txt -- real space radial profile
beam_tform_160201____CMB.txt -- CMB corrected transform
beam_profile_160201____CMB.txt -- CMB corrected profile

The suffixes in use here are:
jitter_ --
beam suitable for use on field maps, because pointing
variance correction and uncertainty have been applied. You
must take into account the pixel window function separately.

jitmap_ --
like jitter_, but the map pixel window function
has also been included. This is primarily useful for quick
real space fitting of sources in the map.

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