Detection of Sub-TeV Gamma Rays from the Galactic Center Direction by CANGAROO-II

TLDR

The study aims to determine whether the GeV source 3EG J1746‑2851 coincides with the newly detected TeV emission and to identify the origin of the gamma rays by combining their spectra. Using the CANGAROO‑II Imaging Atmospheric Cherenkov Telescope, the team measured sub‑TeV gamma‑ray emission from the Galactic Center, detecting a >250 GeV excess and deriving the combined spectrum. They detected a point‑like, soft‑spectrum (∝ E⁻⁴.⁶±⁰.⁵) gamma‑ray signal at the Galactic Center with a flux ≈ 10 % of the Crab at 1 TeV, and set an upper limit on the Galactic halo dark‑matter density.

Abstract

We have detected sub-TeV gamma-ray emission from the direction of the Galactic center (GC) using the CANGAROO-II Imaging Atmospheric Cerenkov Telescope. We detected a statistically significant excess at energies greater than 250 GeV. The flux was 1 order of magnitude lower than that of the Crab Nebula at 1 TeV with a soft spectrum proportional to E-4.6±0.5. The signal centroid is consistent with the GC direction, and the observed profile is consistent with a pointlike source. Our data suggest that the GeV source 3EG J1746-2851 is identical to this TeV source, and we study the combined spectra to determine the possible origin of the gamma-ray emission. We also obtain an upper limit on the cold dark matter density in the Galactic halo.