On the high-energy emissions of compact objects observed with INTEGRAL SPI: Event selection impact on source spectra and scientific results for the bright sources Crab Nebula, GS2023+338 and MAXI J1820+070

Abstract: The INTEGRAL SPI instrument observes the hard X-ray sky from 20 keV up to a few MeV since more than 15 years. In this energy domain, the main emitters are compact objects for which SPI provides spectral information of prime interest. Recently, two transient sources reached very unusual flux levels and have been detected up to a few hundreds of keV with a high significance level. A drastic reduction of the systematic errors is thus required to obtain reliable spectra. This objective is achieved through an analysis including a detailed understanding of the instrument behavior. This paper presents both aspects of the data analysis: we first give a basic description of the instrumental issues, then we present the solution to be implemented in the SPI data analysis (at the event selection stage) and illustrate with a few examples the reliability of the SPI results in the high-energy domain when the data analysis is performed properly. We take benefit from this refined analysis procedure to propose an updated model of the hard X-ray spectral shape of the Crab Nebula. We revisit the high-energy emission observed in GS2023+338 spectra during its 2015 outburst and present the first results from the SPI observations dedicated to the recently discovered transient MAXI J1820+070.