Insight-HXMT measurements of the diffuse X-ray background

We present an X-ray spectrum of the diffuse X-ray background (DXRB) between 1.5 and 120 keV, as measured with the Low-Energy Detector (LE) and the High-Energy Detector (HE) aboard the Insight-HXMT satellite, based on 'blank-sky' observations. LE covers a nominal energy range of 1-15 keV and HE 20-250 keV, but calibration issues and data quality narrowed the energy range for this work. The LE background was directly measured with 'blind' detector modules, while the HE background was derived from Earth-occultation data. With the LE data alone, the measured DXRB spectrum can be well-described by a power law; fitting the LE and HE data jointly, however, a spectral cut-off must be introduced in the model to account for the measurements above 30 keV. Modelling the combined spectrum with a cut-off power law, the best-fitting photon index is 1.40, normalization 9.57 ph cm(-2) s(-1) keV(-1) sr(-1) (at 1 keV), and cut-off energy 55 keV after correcting for the effects of the Earth albedo and atmospheric emission (which are significant in the HE band). Based on the best-fitting cut-off power law, we derived the spectral energy distribution (SED) of the DXRB. The shape of the SED is in general agreement with the published measurements, but the overall normalization is lower by varying amounts, except for the HEAO-1 result, with which our result is in good agreement.

Automated summary

In this study, we present an X-ray spectrum of the diffuse X-ray background (DXRB) between 1.5 and 120 keV based on observations from the Insight-HXMT satellite. Our data analysis shows that the best-fitting model for the DXRB spectrum is a power law with a cutoff energy of 55 keV and a photon index of 1.40.