Separation of gain fluctuations and continuum signals in total power spectrometers with application to COMAP
8 affiliations
- 1Institute of Theoretical Astrophysics, University of Oslo
- 2Department of Physics, Southern Methodist University
- 3Department of Astronomy, Cornell University
- 4California Institute of Technology
- 5Jodrell Bank Centre for Astrophysics, Alan Turing Building, Department of Physics and Astronomy, School of Natural Sciences, The University of Manchester
- 6Department of Physics, University of Miami
- 7Owens Valley Radio Observatory, California Institute of Technology
- 8Department of Physics and Astronomy, University of British Columbia
Abstract
We describe a time-domain technique for separating 1/ f gain fluctuations and continuum signal for a total power spectrometer, such as the CO Mapping Array Project (COMAP) Pathfinder instrument. The 1/ f gain fluctuations of such a system are expected to be common-mode across frequency channels. If the instrument’s system temperature is not constant across channels, a continuum signal exhibits a frequency dependence different from that of common-mode gain fluctuations. Our technique leverages this difference to fit a three-parameter frequency model to each time sample in the time-domain data, separating gain and continuum. We show that this technique can be applied to the COMAP Pathfinder instrument, which exhibits a series of temporally stable resonant noise spikes that effectively act as calibrators, breaking the gain degeneracy with continuum signals. Using both simulations and observations of Jupiter, we explore the effect of a 1/ f prior for the gain model. We show that the model is capable of cleanly separating Jupiter, a bright continuum source, from the gain fluctuations in the scan. The technique has two applications to COMAP. For the COMAP observations performing line intensity mapping (LIM), the technique better suppresses atmospheric fluctuations and foregrounds than the COMAP LIM pipeline. For the Galactic COMAP observations, which map Galactic continuum signals, the technique can suppress 1/ f gain fluctuations while retaining all continuum signals. This is demonstrated by the latest COMAP observations of λ-Orionis, for which our method produces far cleaner maps than a destriper alone, typically reducing the noise power by a factor of 7 on beam scales and up to 15 on larger scales.
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BibTeX
@article{lunde2026separation,
title = {{Separation of gain fluctuations and continuum signals in total power spectrometers with application to COMAP}},
author = {J. G. S. Lunde and P. C. Breysse and D. T. Chung and K. A. Cleary and C. Dickinson and D. A. Dunne and J. O. Gundersen and S. E. Harper and G. A. Hoerning and H. T. Ihle and J. W. Lamb and T. J. Pearson and T. J. Rennie and N.-O. Stutzer},
journal = {Astronomy \& Astrophysics},
year = {2026},
month = oct,
doi = {10.1051/0004-6361/202558006},
url = {https://www.aanda.org/10.1051/0004-6361/202558006},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Separation of gain fluctuations and continuum signals in total power spectrometers with application to COMAP
AU - J. G. S. Lunde
AU - P. C. Breysse
AU - D. T. Chung
AU - K. A. Cleary
AU - C. Dickinson
AU - D. A. Dunne
AU - J. O. Gundersen
AU - S. E. Harper
AU - G. A. Hoerning
AU - H. T. Ihle
AU - J. W. Lamb
AU - T. J. Pearson
AU - T. J. Rennie
AU - N.-O. Stutzer
PY - 2026
DA - 2026/10/27
JO - Astronomy & Astrophysics
DO - 10.1051/0004-6361/202558006
UR - https://www.aanda.org/10.1051/0004-6361/202558006
AB - We describe a time-domain technique for separating 1/ f gain fluctuations and continuum signal for a total power spectrometer, such as the CO Mapping Array Project (COMAP) Pathfinder instrument. The 1/ f gain fluctuations of such a system are expected to be common-mode across frequency channels. If the instrument’s system temperature is not constant across channels, a continuum signal exhibits a frequency dependence different from that of common-mode gain fluctuations. Our technique leverages this difference to fit a three-parameter frequency model to each time sample in the time-domain data, separating gain and continuum. We show that this technique can be applied to the COMAP Pathfinder instrument, which exhibits a series of temporally stable resonant noise spikes that effectively act as calibrators, breaking the gain degeneracy with continuum signals. Using both simulations and observations of Jupiter, we explore the effect of a 1/ f prior for the gain model. We show that the model is capable of cleanly separating Jupiter, a bright continuum source, from the gain fluctuations in the scan. The technique has two applications to COMAP. For the COMAP observations performing line intensity mapping (LIM), the technique better suppresses atmospheric fluctuations and foregrounds than the COMAP LIM pipeline. For the Galactic COMAP observations, which map Galactic continuum signals, the technique can suppress 1/ f gain fluctuations while retaining all continuum signals. This is demonstrated by the latest COMAP observations of λ-Orionis, for which our method produces far cleaner maps than a destriper alone, typically reducing the noise power by a factor of 7 on beam scales and up to 15 on larger scales.
SN - 0004-6361
SN - 1432-0746
ER -