Detection of the Characteristic Pion-Decay Signature in the Molecular Clouds

Abstract

The $\gamma$-ray emission from molecular clouds is widely believed to have a hadronic origin, while unequivocal evidence is still lacking. In this work, we analyze the Fermi-LAT Pass 8 publicly available data accumulated from 2008 August 4 to 2017 June 29 and report the significant detection of a characteristic ${\pi }^0$-decay feature in the $\gamma$-ray spectra of the molecular clouds Orion A and Orion B. This detection provides a direct evidence for the hadronic origin of their $\gamma$-ray emission.

11 pages, 5 figures and 1 table

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