Kavli Affiliate: Shigeki Matsumoto
| First 5 Authors: Yu Watanabe, Alexander Kusenko, Shigeki Matsumoto, ,
| Summary:
We explore whether the unprecedented energy resolution of upcoming gamma-ray
telescopes can uncover relativistic effects in photon spectra resulting from
dark matter (DM) annihilation or decay near the supermassive black hole (SMBH)
at the Galactic Center (GC), specifically, gravitational redshift, Doppler
broadening due to Lorentz boosts, and kinetic energy enhancements arising from
high DM velocities. By modeling DM density and velocity profiles under various
SMBH formation scenarios and DM properties, we calculate the corresponding
gamma-ray spectra and identify the conditions under which SMBH-induced spectral
distortions become observable. We find that, in favorable cases, the observed
spectra encode the DM velocity distribution near the SMBH, enabling potential
discrimination among annihilation mechanisms with different velocity
dependencies. Even when SMBH-induced effects are modest, the upcoming COSI
mission, with sub-percent energy resolution surpassing the typical DM velocity
dispersion at the GC, $mathcal{O}(10^{-3})$, may still be able to detect
subtle Doppler broadening. These results highlight a promising pathway for
determining the origin of gamma-ray signals and probing DM properties through
high-resolution spectral measurements.
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