Methodology and Performance of the Two-Year Galactic Plane Scanning Survey of Insight-HXMT

The Galactic plane scanning survey is one of the main scientific objectives of the Hard X-ray Modulation Telescope (known as Insight-HXMT). During the two-year operation of Insight-HXMT, more than 1000 scanning observations have been performed and the whole Galactic plane ($\rm 0^{\circ}<l<360^{\circ}$, $\rm -10^{\circ}<b<10^{\circ}$) has been covered completely. We summarize the Galactic plane scanning survey of Insight-HXMT for two years, including the characteristics of the scanning data, the data analysis process and the preliminary results of the Low-Energy telescope, the Medium-Energy telescope and the High-Energy telescope. With the light curve PSF fitting method, the fluxes of the known sources in the scanned area as well as the flux errors are obtained for each scanning observation. From the relationships of SNRs and fluxes, the $5σ$ sensitivities of three telescopes of Insight-HXMT are estimated as $\rm \sim7.6\times10^{-11}~erg cm^{-2}~s^{-1}$ ($\rm 3 mCrab,~1-6 keV$), $\rm \sim4.0\times10^{-10}~erg~cm^{-2}~s^{-1}$ ($\rm 20~mCrab,~7-40 keV$) and $\rm \sim2.6\times10^{-10}~erg cm^{-2}~s^{-1}$ ($\rm 18 mCrab,~25-100 keV$) for an individual scanning observation of $2-3$ hours, respectively. Up to September 2019, more than 800 X-ray sources with various types are monitored by the three telescopes and their long-term light curves with three energy bands are obtained to make further scientific analyses.