1/f noise analysis for FAST H I intensity mapping driftscan experiment
Abstract
We investigate the 1/f noise of the Fivehundredmeter Aperture Spherical Telescope (FAST) receiver system using driftscan data from an intensity mapping pilot survey. All the 19 beams have 1/f fluctuations with similar structures. Both the temporal and the 2D power spectrum densities are estimated. The correlations directly seen in the time series data at low frequency f are associated with the sky signal, perhaps due to a coupling between the foreground and the system response. We use singular value decomposition (SVD) to subtract the foreground. By removing the strongest components, the measured 1/f noise power can be reduced significantly. With 20 modes subtraction, the knee frequency of the 1/f noise in a 10MHz band is reduced to $1.8 \times 10^{3}\, {\rm Hz}$, well below the thermal noise over 500s timescale. The 2D power spectra show that the 1/ftype variations are restricted to a small region in the timefrequency space and the correlations in frequency can be suppressed with SVD modes subtraction. The residual 1/f noise after the SVD mode subtraction is uncorrelated in frequency, and a simple noise diode frequencyindependent calibration of the receiver gain at 8s interval does not affect the results. The 1/f noise can be important for H I intensity mapping, we estimate that the 1/f noise has a knee frequency (f_{k}) ~ 6 × 10^{4} Hz, and time and frequency correlation spectral indices (α) ~ 0.65, (β) ~ 0.8 after the SVD subtraction of 30 modes. This can bias the H I power spectrum measurement by 10 per cent.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 December 2021
 DOI:
 10.1093/mnras/stab2728
 arXiv:
 arXiv:2109.06447
 Bibcode:
 2021MNRAS.508.2897H
 Keywords:

 methods: data analysis;
 methods: statistical;
 cosmology: observation;
 largescale structure of Universe;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 13 pages,17 figures, MNRAS accepted