Fermi LAT Discovery of Extended Gamma-Ray Emissions in the Vicinity of the HB3 Supernova Remnant

TL;DR

This paper reports the discovery of extended gamma-ray emissions near the HB3 supernova remnant, likely caused by interactions of accelerated particles with surrounding interstellar gas, providing insights into cosmic ray acceleration.

Contribution

First detection of extended gamma-ray emission associated with HB3 SNR and W3 complex, linking gamma rays to cosmic ray interactions with interstellar gas.

Findings

Gamma-ray emission correlates with interstellar gas and SNR.

Neutral pion decay explains gamma-ray origin.

W3 gamma-ray emission consistent with cosmic ray irradiation.

Abstract

We report the discovery of extended gamma-ray emission measured by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region of the supernova remnant (SNR) HB3 (G132.7+1.3) and the W3 HII complex adjacent to the southeast of the remnant. W3 is spatially associated with bright 12CO (J=1-0) emission. The gamma-ray emission is spatially correlated with this gas and the SNR. We discuss the possibility that gamma rays originate in interactions between particles accelerated in the SNR and interstellar gas or radiation fields. The decay of neutral pions produced in nucleon-nucleon interactions between accelerated hadrons and interstellar gas provides a reasonable explanation for the gamma-ray emission. The emission from W3 is consistent with irradiation of the CO clouds by the cosmic rays accelerated in HB3.