Restrictions on parameters of sterile neutrino dark matter from observations of galaxy clusters

We find restrictions on the mass and mixing angle of the dark matter sterile neutrinos using x-ray observations of Coma and Virgo galaxy clusters with XMM-Newton satellite. In the absence of clearly detectable line, we present detailed analysis of various methods of putting restrictions on mass and mixing angle of sterile neutrino. Our analysis provides significant improvement over our previous results, coming from XRB background measurements. We also discuss restrictions from Virgo cluster by other authors and compare our results with them.

Figure 1

Solid line: exclusion plot from the total flux restriction from the circular region with radius 11 arcmin in the center of Coma cluster. Dotted lines represent ${sin}^2(2\theta )m_s^5=\mathrm{const}$ lines, corresponding to the total flux at energies 0.5 keV and 8.5 keV (in the 200 eV energy bin).

Figure 2

Exclusion plot based on the restrictions derived from a total flux from Coma 3 peripheral observation (thick dashed line) as compared with Coma center (solid line). Thinner dashed lines represent $m_s^5{sin}^2(2\theta )=\mathrm{const}$ with normalization corresponding to fluxes at 1 keV and 7 keV.

Figure 3

Comparison between Coma center (solid curve) and Coma 3 (dotted curve) fluxes (per 200 eV energy bin).

Figure 4

Restrictions based on the total flux from the circle with the radius ${11}^{\prime }$ with the center at M87 (solid line). Thick dotted line represents the data for Coma periphery—same as on Fig. 2. Thinner dotted line—restriction (4) from [10].

Figure 5

Solid line: exclusion plot based on statistical analysis from Coma center observation (circular region of the radius 11 arcmin around the center of the cluster). Dotted line—restriction based on the total flux from the same region (curve from Fig. 1). Arrows mark the positions of lines detected at $\ge 3\sigma$ level.

Figure 6

Solid line: exclusion plot based on statistical analysis from Coma 3 peripheral observation of Sec. 3a2. Dotted line—restriction based on the total flux from the same region (curve from Fig. 2).

Figure 7

Restrictions from the statistical analysis of the periphery (ring 9–11 arcmin) around M87. Solid line shows the bounds obtained assuming a cut-off powerlaw model for the background emission. Dot-dashed line shows the bound obtained assuming the $\mathtt{M}\mathtt{E}\mathtt{K}\mathtt{A}\mathtt{L}$ model for the background emission. The arrows show the narrow lines found at $\ge 3\sigma$ level on top of (both) background models. The statistical analysis restrictions are about an order of magnitude better that the one, coming from the total flux, measured from the same region (dotted line) at small energies ($m_s\lesssim 8\mathrm{keV}$ and comparable to the total flux restrictions at high energies, as statistical error of the data grows. Dashed line represent the XRB restrictions (4).

Figure 8

Exclusion plot for parameters of sterile neutrino, based on analysis of the cluster of the Coma and Virgo clusters of galaxies. The solid line represents the best “total flux” restriction, coming from the Coma periphery (“Coma 3”) observation, while the long dashed line comes from statistical analysis of Coma center. Comparable restrictions (shown in dotted line) come from statistical analysis of the ring $9^{\prime }–{11}^{\prime }$ around M87. The straight short dashed line represents the XRB restrictions from [10], while parallel to it short dashed line represents the averaged current bound from Coma center statistical analysis, showing the improvement about a factor of 7 compared to the XRB analysis.

Figure 9

Comparison of WEBSPEC simulations of [9] (lower line) with actual XMM observation of M87—upper line.

Figure 10

Folded (a) and unfolded (b) XMM-Newton and Beppo-SAX spectrum of the Coma galaxy cluster. The simple phenomenological model used to fit the data consists of a cut-off powerlaw modified by the galactic absorption and four Gaussian lines. The model parameter values are given in the text.