Lei Feng, Qiang Yuan, Peng-Fei Yin, Xiao-Jun Bi, Mingzhe Li
The globular clusters are probably good targets for dark matter (DM) searches
in $\gamma$-rays due to the possible adiabatic contraction of DM by baryons. In
this work we analyse the three-year data collected by {\it Fermi} Large Area
Telescope of globular clusters NGC 6388 and M 15 to search for possible DM
signals. For NGC 6388 the detection of $\gamma$-ray emission was reported by
{\it Fermi} collaboration, which is consistent with the emission of a
population of millisecond pulsars. The spectral shape of NGC 6388 is also shown
to be consistent with a DM contribution if assuming the annihilation final
state is $b\bar{b}$. No significant $\gamma$-ray emission from M 15 is
observed. We give the upper limits of DM contribution to $\gamma$-ray emission
in both NGC 6388 and M 15, for annihilation final states $b\bar{b}$, $W^+W^-$,
$\mu^+\mu^-$, $\tau^+\tau^-$ and monochromatic line. The constraints are
stronger than that derived from observation of dwarf galaxies by {\it Fermi}.
View original:
http://arxiv.org/abs/1112.2438
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