High Energy Gamma-Ray Emission from the Loop I region

TL;DR

This study detects a gamma-ray excess in the Loop I region, a nearby radio loop, using Fermi-LAT data, suggesting a link between high-energy emission and the structure's synchrotron features.

Contribution

First detection of gamma-ray excess associated with Loop I using Fermi-LAT, linking high-energy emission to the radio loop's structure.

Findings

Gamma-ray excess observed in Loop I region.

The excess shows an arc-shaped structure similar to synchrotron emission.

Supports the hypothesis of cosmic-ray acceleration in Loop I.

Abstract

Loop I is a nearby giant radio loop spanning over 100 degrees and centered on the Sco-Cen OB association. It may correspond to a superbubble formed by the joint action of stellar winds and supernova remnants. ROSAT observations revealed that the region is filled with a hot gas possibly reheated by successive supernova explosions. The brightest rim of Loop I, called the North Polar Spur (NPS), extends to the north along 30 degrees in longitude, at a distance of about 100 pc from the Sun. Early searches for high-energy gamma rays associated with electrons or protons accelerated by Loop I were performed with SAS-II, COSB and EGRET. But a detector with better performance and higher statistics is required to distinguish the faint signal from the NPS from broad structures in the Galactic interstellar emission, such as the inverse Compton emission from cosmic-ray electrons scattering the interstellar radiation field. We modelled the gamma-ray emission of the Galaxy and compared it to the Fermi-LAT photons detected above 300 MeV. We observe an excess of photons in the direction of Loop I. This excess exhibit a large arc-shaped structure similar to those seen in synchrotron emission.