The Diffuse X-Ray Background of the Insight-HXMT/LE Telescope in the Galactic Plane

Abstract

Accurately estimating of diffuse X-ray background (DXB) is essential for the investigation of sources in the Galactic plane observed with Insight-HXMT/LE, which is a collimated telescope in the soft X-ray energy band with a relatively large field of view. In the high-Galactic-latitude region, DXB is dominated by the cosmic X-ray background, which is almost uniform, but DXB in the Galactic plane region is more complex due to the Galactic H i absorption and the contribution of the Galactic ridge X-ray emission. This study, as a part of background estimation of LE, focuses on estimating the contribution of DXB in the Galactic plane to Insight-HXMT/LE observations. We calculate DXB confined in a region of 0 degrees < l < 360 degrees and divide b divide < 10 degrees, where l and b denote Galactic longitude and latitude, respectively, with the first 3 yr of Galactic-plane-scanning survey data of Insight-HXMT/LE. The Galactic plane is divided into 360 x 20 small pixels (1 degrees x 1 degrees per pixel), and a DXB spectrum is obtained for each pixel. An indirect method is developed for the pixels of the bright source regions, which brings a systematic error of similar to 10%. The systematic error brought by the satellite attitude is similar to 7% on average for all the pixels in the Galactic plane. The LE DXB spectrum obtained in this study is consistent with that reported by RXTE's Proportional Counter Array.