Fermi-LAT observations of the Sagittarius B complex

TL;DR

This study analyzes five years of Fermi-LAT gamma-ray data from the Sagittarius B complex to assess cosmic-ray distribution and spectrum, finding it consistent with local cosmic rays but with a slight over-density at intermediate energies.

Contribution

It provides the first detailed gamma-ray spectrum of Sagittarius B using Fermi-LAT data and compares it with local cosmic-ray spectra, offering insights into cosmic-ray uniformity in the Galaxy.

Findings

Gamma-ray flux fits local cosmic-ray spectrum

Mass estimate of Sagittarius B matches previous data

Evidence of a small over-density at 1-10 GeV energies

Abstract

Aims. We use 5 years of Fermi-LAT data towards the Galactic-centre giant molecular cloud complex, Sagittarius B, to test questions of how well-mixed the Galactic component of cosmic rays are and what the level of the cosmic-ray sea in different parts of the Galaxy is. Methods. We use dust-opacity maps from the Planck satellite to obtain independent methods for background subtraction and an estimate for the mass of the region. We then present high-quality spectra of gamma-ray emission from 0.3 to 30 GeV and obtain an estimate of the cosmic-ray spectrum from the region. Results. We obtain an estimate of the mass of the region of $1.5 \pm 0.2 \times 10^7~\rm M_{\odot}$ using the Planck data, which agrees well with molecular-line-derived estimates for the same region. We find the the gamma-ray flux from this region is fitted well with a cosmic-ray spectrum that is the same as is observed locally, with evidence of a small over-density at intermediate (1-10 GeV) energies. Conclusions. We conclude that the gamma-ray and cosmic-ray spectrum in the region can be well-fitted using a local cosmic-ray spectrum.