HiFAST : An HI Data Calibration and Imaging Pipeline for FAST II. Flux Density Calibration

Abstract

Accurate flux density calibration is essential for precise analysis and interpretation of observations across different observation modes and instruments. In this research, we firstly introduce the flux calibration model incorporated in HIFAST pipeline, designed for processing HI 21-cm spectra. Furthermore, we investigate different calibration techniques and assess the dependence of the gain parameter on the time and environmental factors. A comparison is carried out in various observation modes (e.g. tracking and scanning modes) to determine the flux density gain ($G$), revealing insignificant discrepancies in $G$ among different methods. Long-term monitoring data shows a linear correlation between $G$ and atmospheric temperature. After subtracting the $G$--Temperature dependence, the dispersion of $G$ is reduced to $<$3% over a one-year time scale. The stability of the receiver response of FAST is considered sufficient to facilitate HI observations that can accommodate a moderate error in flux calibration (e.g., $>\sim 5\%$) when utilizing a constant $G$ for calibration purposes. Our study will serve as a useful addition to the results provided by Jiang et al. (2020). Detailed measurement of $G$ for the 19 beams of FAST, covering the frequency range 1000 MHz -- 1500 MHz can be found on the HIFAST homepage: https://hifast.readthedocs.io/fluxgain.

14 pages, 15 figures, accepted by RAA

References in corpus (7)

• The Five-Hundred-Meter Aperture Spherical Radio Telescope (FAST) Project
• The FAST all sky HI survey (FASHI): The first release of catalog
• Galaxy redshift surveys selected by neutral hydrogen using FAST
• FEASTS: IGM cooling triggered by tidal interactions through the diffuse HI phase around NGC 4631
• HiFAST: an HI data calibration and imaging pipeline for FAST
• Radio Frequency Interference Mitigation and Statistics in the Spectral Observations of FAST
• The FAST Ultra-Deep Survey (FUDS): observational strategy, calibration and data reduction

Cited by in corpus (5)

• HiFAST: An HI Data Calibration and Imaging Pipeline for FAST III. Standing Wave Removal
• Observation of HI around three satellite galaxies of the M31 with the FAST: Andromeda II, NGC 205, and NGC 185
• FASHI: A search for extragalactic OH megamasers with FAST
• HiFAST: An HI data calibration and imaging pipeline for the FAST IV: The stray-radiation correction
• The FAST Hundred-Deg${}^2$ HI Deep (HD${}^2$) Survey: Early Results from the Pilot Survey