Exploring Sagittarius A* in gamma-rays with Fermi LAT Telescope

Abstract

Sagittarius A * (Sgr A * )-the supermassive black hole (SMBH) in the center of our galaxy-has been identified in most of the electromagnetic spectrum, from radio to Xrays. Diffuse gamma-ray emission has been observed around Sgr A * and a gamma-ray point source has been detected coinciding with the SMBH's position, although there is still no definitive association between the two. In this work, we have used ∼11 years of Fermi Large Area Telescope (LAT) observations of the point source 4FGL J1745.6−2859 and performed a detailed analysis across four energy bands. Our goal is to elucidate the nature of the gamma-ray emission at the Galactic Center (GC) and whether it is associated with the SMBH. We find that the centroids of the emission approach Sgr A * 's location as the energy increases and they are spatially associated with gas-rich regions in the GC.Assuming that the gamma-ray point source is located at the GC, we estimate a luminosity of 2.61 × 10 36 erg s −1 in the 100 MeV to 500 GeV energy range. This is consistent with Sgr A * 's bolometric luminosity. Based on the point source properties, we ruled out several potential candidates for its nature and favor a cosmic ray origin accelerated by-or in the vicinity of-the SMBH. We also created light curves (LCs), with time bins as short as 15 days, in search of variability in the 4FGL J1745.6−2859 gamma-ray flux. In contrast with Sgr A * 's flaring behavior in longer wavelengths, we detect that its gamma-ray flux distribution is compatible with a Gaussian, representative of a normal random process, hinting that the gamma-ray emission mechanism differs substantially from the low-energy regime. Finally, 4FGL J1745.6−2859's spectral energy distribution (SED) shows a "piondecay bump" characteristic of gamma-ray hadronic emission. Its SED is also compatible with several hadronic models for Sgr A * 's gamma-ray emission. Our results indicate that the point source at the GC is indeed the gamma-ray counterpart of Sgr A * in the GeV range. The characteristics of this emission-its spatial coincidence with gas reservoirs, energetics, lack of variability and SED-suggest that hadronic processes are likely behind its origin.