Direct x-ray constraints on sterile neutrino warm dark matter

Abstract

Warm dark matter (WDM) might more easily account for small scale clustering measurements than the heavier particles typically invoked in Λ cold dark matter (ΛCDM) cosmologies. In this paper, we consider a ΛWDM cosmology in which sterile neutrinos νs, with a mass ms of roughly 1-100 keV, are the dark matter. We use the diffuse X-ray spectrum (total minus resolved point source emission) of the Andromeda galaxy to constrain the rate of sterile neutrino radiative decay: νs → νe,µ,τ + γ. Our findings demand that ms < 3.5 keV (95% C.L.) which is a significant improvement over the previous (95% C.L.) limits inferred from the X-ray emission of nearby clusters, ms < 8.2 keV (Virgo A) and ms < 6.3 keV (Virgo A + Coma).

Probing the nature of dark matter with cosmic x rays: Constraints from “dark blobs” and grating spectra of galaxy clusters

“…This makes it impossible to optimize the ratio of expected dark matter signal to noise from x ray emitting baryons in the observational field of view (as described by [13][14][15][16]). The spectral resolution of a grating spectrometer decreases proportionally to the angular extension of the source.…”

“…The flux obtained with the slice method is almost identical to the flux obtained by giving the slice the shape of a Gaussian centered at the slice energy, and with the width and the maximum at the value of the model fitted to the spectrum. Other methods for constraining the flux (for example [13,15]) can give stronger, but less conservative or robust, results. For a discussion of different methods see [23].…”

“…5 (color online). The observational constraints from the dark matter blob of Abell 520 (red/dark) together with the Tremaine-Gunn limit (hatched, [37]) and earlier x-ray constraints (gray, [13][14][15][16][17][18]38]). …”

“…The decay rate of any dark matter candidate with a radiative two-body decay can be constrained from observations of dark matter concentrations (for references see [11][12][13][14][15][16][17][18]). The strongest constraints are obtained from studying dark matter dominated regions, and with instruments with high spectral resolution since the decay line is expected only to suffer negligible broadening due to motion of the dark matter.…”

X-ray photons from late-decaying majoron dark matter

“…Figure 3. Upper limit on the decay rate from NGC3227 (red), the Milky Way halo observed with a prototype cryogenic spectrometer (salmon) [27], XMM observations of the Milky Way (sand) [35], Chandra observations of the Bullet Cluster [30] and M31 [36,37] (orange), HEAO-1 observations of the diffuse x-ray background (aquamarine) [25,26], INTEGRAL SPI line search in the Milky Way halo (blue) [38,39]. Filled regions are excluded.…”