Figure 1

The three unresolved CXB spectra [CDFN-VF (black), CDFN-F (red), and CDFS (blue)] in the 0.4–10 keV band. They are fit well by a simple model consisting of a power law absorbed by the Galactic hydrogen column representing the extragalactic component, plus unabsorbed local warm thermal emission. All three spectra are fit well, with a total reduced ${\chi }^2$ of 0.87, and no residual linelike features are seen. Only energies $E>0.8\mathrm{keV}$ are used for the line flux limits. See text for details.Reuse & Permissions

Figure 2

Shown are the limits on the flux in a line as a function of energy from the CDFN-VF, CDFN-F, and CDFS. For each line energy in the range 0.8–9 keV, all model parameters were allowed to vary while deriving upper limits on the sterile neutrino line normalization. The upper line and (cyan) band are the $3\sigma$ limit, with the band representing uncertainty in the detector background modeling. The lower band and line correspond to that from the $2\sigma$ limits. The diagonal band is the range of expected line flux from the MW halo as a function of energy for the sterile neutrino in a DW production model.Reuse & Permissions

Figure 3

Full parameter space constraints for the sterile neutrino production models, assuming sterile neutrinos constitute the dark matter. Contours labeled with lepton number $L=0$, $L=0.003$, $L=0.01$, $L=0.1$ are production predictions for constant comoving density of ${\Omega }_s=0.24$ for $L=0$, and ${\Omega }_s=0.3$ for nonzero $L$ [29]. Constraints from the CXB with the minimal MW halo model are in the solid (blue) region, while the maximal MW halo model excludes the adjacent diagonally hatched region. Also shown are exclusion regions from the diffuse X-ray background (green) [67], from XMM-Newton observations of the Coma and Virgo clusters (light blue) [68], observations of Andromeda (M31) in wide hatching [40], and limits from the MW by Boyarsky et al. [41] (BMW). The region at $m_s<0.4\mathrm{keV}$ is ruled out by a conservative application of the Tremaine-Gunn bound [10]. The gray region to the right of the $L=0$ case is where sterile neutrino dark matter is over-produced. The constraint from the MW calorimeter soft X-ray background observation is the star and arrow, marked “Calor.” Also shown is the horizontal band of the mass scale consistent with producing a 100–300 pc core in the Fornax dwarf galaxy [5]. The nonresonant and resonant production curves come from Refs. 28, 29, respectively.Reuse & Permissions

Figure 4

The upper panel is the spectrum soft X-ray background as measured by McCammon et al. [54]. The lower panel shows the atomic line model, detector response function (blue) and expected contribution ($\times 60$) due to sterile neutrino decay of the DW production model with the minimal (lower, green) and maximal (upper, red) MW halo models.Reuse & Permissions