Deciphering the spectral bumps of Galactic cosmic rays through gamma-ray observations of nearby molecular clouds

Abstract

The observed spectral bump in cosmic-ray (CR) proton and helium spectra, along with the phase and amplitude evolution of CR dipole anisotropy, provide plausible yet indirect evidence for the presence of a nearby CR source. This study investigates the potential of giant molecular clouds (GMCs) located near the solar system to act as natural probes of CRs from the nearby source, with their gamma-ray emissions serving as indicators of spatial variations in CR flux within the solar neighborhood resulting from this source. We show that a nearby source, accounting for the CR data, could imprint distinct features on the $\gamma$-ray spectra of different GMCs. We expect that these features are detectable by LHAASO and upcoming high-energy $\gamma$-ray observatories, providing a powerful test for the hypothesized nearby source. Notably, we find that determining the energy dependence of the $\gamma$-ray spectral index offers a promising approach to investigate the nearby source and constrain its distance. Conversely, if the spectral bump is a widespread Galactic phenomenon, the energy dependence would exhibit uniformity across all GMCs, distinguishing the underlying mechanism accounting for the spectral bump from the scenario involving a nearby source.

arXiv comment10 pages, 6 figures

References in corpus (29)

• Fermi Large Area Telescope Second Source Catalog
• Cosmic-ray propagation and interactions in the Galaxy
• PAMELA Measurements of Cosmic-ray Proton and Helium Spectra
• The Origin of Galactic Cosmic Rays
• On the knee in the energy spectrum of cosmic rays
• Discrepant hardening observed in cosmic-ray elemental spectra
• Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
• Measurement of the cosmic-ray proton spectrum from 40 GeV to 100 TeV with the DAMPE satellite
• Proton and Helium Spectra from the CREAM-III Flight
• Science with the Cherenkov Telescope Array
• The origin of Galactic cosmic rays: challenges to the standard paradigm
• Origin of the Cosmic Ray Spectral Hardening
• Measurement of the cosmic ray helium energy spectrum from 70 GeV to 80 TeV with the DAMPE space mission
• Propagation of cosmic rays in the AMS-02 era
• Cosmic-ray transport from AMS-02 B/C data: benchmark models and interpretation
• Cosmic ray acceleration at oblique shocks
• A new universal cosmic-ray knee near the magnetic rigidity 10 TV with the NUCLEON space observatory
• Spatial-Dependent Diffusion of Cosmic Rays and the Ratio of pbar/p, B/C
• Origin of Small-Scale Anisotropies in Galactic Cosmic Rays
• Probing the "Sea" of Galactic Cosmic Rays with Fermi-LAT
• Cosmic ray spectrum in the local Galaxy
• Gamma Rays from Molecular Clouds
• Indication of nearby source signatures of cosmic rays from energy spectra and anisotropies
• Understanding hadronic gamma-ray emission from supernova remnants
• Implications on the origin of cosmic rays in light of 10 TV spectral softenings
• DAMPE proton spectrum indicates a slow-diffusion zone in the nearby ISM
• Measurement of the cosmic p+He energy spectrum from 50 GeV to 0.5 PeV with the DAMPE space mission
• Simulation study of performance of the Very Large Area gamma-ray Space Telescope
• Probing the Sea of Cosmic Rays by Measuring Gamma-Ray Emission from Passive Giant Molecular Clouds with HAWC