Is dark matter visible by galactic gamma rays?
W de BOER
Physikhochhaus, IEKP, Universit\"at
E-mail: deboer@ekp.uni-karlsruhe.de
Abstract. The
EGRET excess in the diffuse galactic gamma ray data
above 1 GeV
shows all features expected from dark matter WIMP
annihilation: (a) It is present and
has the same spectrum in all sky
directions, not just in the
galactic plane. (b) The intensity of the
excess shows the $1/r^2$ profile
expected for a flat rotation curve
outside the galactic disc with an
additionally interesting
substructure in the disc in the
form of a doughnut-shaped ring at 14
kpc from
the centre of the galaxy. At this radius
a ring of stars
indicates the probable infall of a dwarf galaxy, which can explain
the increase in DM density.
From the spectral shape of the excess the WIMP mass is
estimated to
be between 50 and 100 GeV, while from the intensity the halo profile
is reconstructed. Given the mass
and intensity of the WIMPs the mass
of the ring can be calculated, which is shown to
explain the
peculiar change of slope in the
rotation curve at about 11 kpc.
These results are model-independent in the sense that only
the {\it
known shapes} of signal and
background were fitted with free
normalization factors, thus being
independent of model-dependent
flux calculations. The statistical
significance is more than
$10\sigma$ in comparison with a fit of the conventional
galactic
model to the EGRET data. These
signals of dark matter annihilation
are compatible with supersymmetry including all electroweak
constraints. The statistical
significance combined with all features
mentioned above provide an
intriguing hint that the EGRET excess is
indeed
a signal from dark matter annihilation.
Keywords. Gamma rays; milky
way; cosmology; elementary particles.
PACS Nos 95.35.+d; 98.35.Gi; 98.70.Rz;
98.80.Bp