HiFAST: An H I data calibration and imaging pipeline for the FAST IV: The stray-radiation correction

Stray radiation is a considerable challenge for radio telescopes, requiring careful assessment due to its effects. This is crucial when the strong background flux from side lobes significantly affects the total flux, especially for extended sources. In this study, we introduced the beam pattern of the L-band receiver on the Five-hundred-meter Aperture Spherical Telescope (FAST), covering various frequencies based on recent observations. We discovered that the main beam efficiency of all beams exceeds 90\% throughout the L band frequencies, with efficiency decreasing slowly as frequency increases. Subsequently, we developed a module to mitigate stray radiation effects, incorporating it into FAST's standard H I data reduction process, referred to as HiFAST. Our analysis shows that side lobe flux's influence, particularly for extended sources with significant surface density gradients, necessitates detailed evaluation. Corrections for the extended M33 galaxy can reach up to 20\%. Moreover, the pattern data presented here is vital for studying HI intensity maps at high redshift. The module, along with HiFAST and beam pattern data across 15 frequency bins, can be accessed at \textrm{https://hifast.readthedocs.io}The dataset contains beam pattern of FAST 19-beam-receiver at 1050-1110MHz and 1330-1430MHz.The dataset is given in the frequency of every 10 MHz.The name of each file is the center of the frequency band.index:pattern-M*-1055MHz.fitspattern-M*-1065MHz.fitspattern-M*-1075MHz.fitspattern-M*-1085MHz.fitspattern-M*-1125MHz.fitspattern-M*-1135MHz.fitspattern-M*-1335MHz.fitspattern-M*-1345MHz.fitspattern-M*-1355MHz.fitspattern-M*-1365MHz.fitspattern-M*-1375MHz.fitspattern-M*-1385MHz.fitspattern-M*-1395MHz.fitspattern-M*-1405MHz.fitspattern-M*-1415MHz.fits