On gamma-ray sources, supernova remnants, OB associations, and the origin of cosmic rays

Abstract

Spatial coincidences between supernova remnants and OB associations or H II regions are sought, and a list of about 30 objects (referred to as 'SNOBs') is obtained. On the basis of COS B data it is found that five, or perhaps six, of 11 as-yet unidentified gamma-ray sources are associated with SNOBs and that as many as three-fourths of the best-identified SNOBs may be observable in gamma rays. It is suggested that if a substantial proportion of the observed gamma rays originates from neutral-pion decay, SNOBs would appear to be a major source of galactic cosmic rays. A phenomenological scenario is considered in which cosmic rays are produced by a two-step process whereby low-energy particles are injected by the young member stars of an OB association and are subsequently accelerated by the shock wave from a nearby supernova explosion.