Study of the very high energy gamma-ray spectrum from the Galactic Center and future prospects

TL;DR

This paper analyzes gamma-ray data from the Galactic Center, compares different spectral cutoff models, constrains dark matter density profiles, and forecasts future observations with the Cherenkov Telescope Array.

Contribution

It provides a detailed spectral analysis of the Galactic Center gamma-ray source, compares exponential and super-exponential cutoff models, and discusses future CTA observations.

Findings

Super-exponential cutoff fits the spectrum as well as exponential.

Dark matter interpretation is less consistent with the data.

Forecasts for CTA will help distinguish spectral cutoff types.

Abstract

Ground-based gamma ray observations of the Galactic Center region have revealed a high energy gamma ray source spatially coincident with the gravitational centroid of our Galaxy. The pointlike emission detected by H.E.S.S. exhibits an energy cut-off at about 10 TeV. We identify the parameters of the best fit of the exponential and the super-exponential cutoff models to the spectrum of the pointlike source and find that super-exponential one provides a similar quality of the fit to the spectrum of the pointlike source as the best-fit exponential cutoff model, while a dark matter interpretation does not provide as good a fit in the whole energy range of the signal. Based on the magnitude of the flux we derive constraints in the plane of the slope of the density profile $\gamma$ and the critical radius, below which the density is assumed to be constant, $r_c$. Motivated by recent results on the spectrum and morphology from H.E.S.S. and by the possible observation of a super-exponential cutoff, we forecast the observations of super-exponential versus exponential cut-offs by the upcoming Cherenkov Telescope Array (CTA). We derive a formula for $J$-factor in the small angle approximation and propose approximate morphological constraints on the central source.