Context. Recent findings of line emission at 3.5 keV in both individual and stacked X-ray spectra of galaxy clusters have been speculated to have dark matter origin. Aims. If the origin is indeed dark matter, the emission line is expected to be detec
table from the Milky Way dark matter halo. Methods. We perform a line search in public Chandra X-ray observations of the region near Sgr A*. We derive upper limits on the line emission flux for the 2.0-9.0 keV energy interval and discuss their potential physical interpretations including various scenarios of decaying and annihilating dark matter. Results. While find no clear evidence for its presence, the upper flux limits are not inconsistent with the recent detections for conservative mass profiles of the Milky Way. Conclusions. The results depends mildly on the spectral modelling and strongly on the choice of dark matter profile.
There is a long-standing discrepancy between galaxy cluster masses determined from X-ray and gravitational lensing observations of which Abell 1689 is a well-studied example. In this work we take advantage of 180 ks of Chandra X-ray observations and
a new weak gravitational study based on a Hubble Space Telescope mosaic covering the central 1.8 Mpc x 1.4 Mpc to eliminate the mass discrepancy. In contrast to earlier X-ray analyses where the very circular surface brightness has been inferred as Abell 1689 being spherically symmetric and in hydrostatic equilibrium, a hardness ratio map analysis reveals a regular and symmetric appearing main clump with a cool core plus some substructure in the North Eastern part of the cluster. The gravitational lensing mass model supports the interpretation of Abell 1689 being composed of a main clump, which is possibly a virialized cluster, plus some substructure. In order to avoid complications and mis-interpretations due to X-ray emission from the substructure, we exclude it from the mass reconstruction. Comparing X-ray and lensing mass profiles of the regular main part only, shows no significant discrepancy between the two methods and the obtained mass profiles are consistent over the full range where the mass can be reconstructed from X-rays (out to approx. 1 Mpc). The obtained cluster mass within approx. 875 kpc derived from X-rays alone is 6.4 plus/minus 2.1 x 10^14 solar masses compared to a weak lensing mass of 8.6 plus/minus 3.0 x 10^14 solar masses within the same radius.
An attractive way to generate neutrino masses as required to account for current neutrino oscillation data involves the spontaneous breaking of lepton number. The resulting majoron may pick up a mass due to gravity. If its mass lies in the kilovolt s
cale, the majoron can play the role of late-decaying Dark Matter (LDDM), decaying mainly to neutrinos. In general the majoron has also a sub-dominant decay to two photons leading to a mono-energetic emission line which can be used as a test of the LDDM scenario. We compare expected photon emission rates with observations in order to obtain model independent restrictions on the relevant parameters. We also illustrate the resulting sensitivities within an explicit seesaw realisation, where the majoron couples to photons due to the presence of a Higgs triplet.
