Towards Robust Detection of a Faint Narrow Line in X-Rays – the Role of Continuum-Induced Systematics

Abstract

Some of recent detections of a narrow emission line at ∼3.5 keV have been accompanied by subsequent non-detections in the same sources, raising discussion about the actual level of systematic errors. In this paper, we study the systematics caused by an imperfect knowledge of a continuum model. Our simple theoretical estimate and detailed modeling of simulated spectra allow us to calculate the value of this "continuum-induced" systematics for the first time. We show that, for some objects such as the M31 central part or the Draco dwarf spheroidal galaxy, the obtained level of systematics within a well-defined continuum model allows one to fully reconcile the controversial results claimed previously by different groups of authors. To minimize the effect of "continuum-induced" systematics, we show that one should reasonably decrease the size of the spectral bin and increase the modeled energy range. K e y w o r d s: X-rays, general line, identification of the dark matter.