BEYONDPLANCK

IX. Bandpass and beam leakage corrections

¹ Institute of Theoretical Astrophysics, University of Oslo, Blindern, Oslo, Norway
e-mail: t.l.svalheim@astro.uio.no
² San Diego Supercomputer Center, University of California, San Diego, USA
³ Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, Milano, Italy
⁴ INAF/IASF Milano, Via E. Bassini 15, Milano, Italy
⁵ INFN, Sezione di Milano, Via Celoria 16, Milano, Italy
⁶ INAF – Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, Trieste, Italy
⁷ Planetek Hellas, Leoforos Kifisias 44, Marousi 151 25, Greece
⁸ Department of Astrophysical Sciences, Princeton University, Princeton, NJ, 08544, USA
⁹ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, USA
¹⁰ Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2, Helsinki, Finland
¹¹ Helsinki Institute of Physics, University of Helsinki, Gustaf Hällströmin katu 2, Helsinki, Finland
¹² Computational Cosmology Center, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
¹³ Haverford College Astronomy Department, 370 Lancaster Avenue, Haverford, PA, USA
¹⁴ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
¹⁵ Dipartimento di Fisica, Università degli Studi di Trieste, Via A. Valerio 2, Trieste, Italy

Received: 10 January 2022
Accepted: 25 February 2022

Abstract

We discuss the treatment of bandpass and beam leakage corrections in the Bayesian BEYONDPLANCK cosmic microwave background (CMB) analysis pipeline as applied to the Planck LFI measurements. As a preparatory step, we first applied three corrections to the nominal LFI bandpass profiles, including the removal of a known systematic effect in the ground measuring equipment at 61 GHz, along with a smoothing of standing wave ripples and edge regularization. The main net impact of these modifications is an overall shift in the 70 GHz bandpass of +0.6 GHz. We argue that any analysis of LFI data products, either from Planck or BEYONDPLANCK, should use these new bandpasses. In addition, we fit a single free bandpass parameter for each radiometer of the form Δ_i = Δ₀ + δ_i, where Δ₀ represents an absolute frequency shift per frequency band and δ_i is a relative shift per detector. The absolute correction is only fitted at 30 GHz, with a full χ²-based likelihood, resulting in a correction of Δ₃₀ = 0.24 ± 0.03 GHz. The relative corrections were fitted using a spurious map approach that is fundamentally similar to the method pioneered by the WMAP team, but excluding the introduction of many additional degrees of freedom. All the bandpass parameters were sampled using a standard Metropolis sampler within the main BEYONDPLANCK Gibbs chain and the bandpass uncertainties were thus propagated to all other data products in the analysis. In summary, we find that our bandpass model significantly reduces leakage effects. For beam leakage corrections, we adopted the official Planck LFI beam estimates without any additional degrees of freedom and we only marginalized over the underlying sky model. We note that this is the first time that leakage from beam mismatch has been included for Planck LFI maps.