The diffuse neutrino emission of the Galaxy, detected by IceCube at 5.7 sigma, opens a direct window into hadronic interactions of cosmic rays with interstellar gas. Existing diffuse background templates typically assume a single cosmic-ray injection spectrum across all energies and do not account for independent contributions from different accelerator populations. Meanwhile, supernova remnants are unlikely to accelerate particles to PeV energies, while microquasars with relativistic jets are natural candidates for PeV accelerators. This work fits into a series of recent studies linking diffuse neutrinos and gamma rays to specific source classes, but it is the first to separate these classes in a unified numerical scheme.
The authors model the spatiotemporal distribution of microquasars and supernova remnants in the Galaxy, assigning their positions according to a radial profile and an exponential vertical distribution with a characteristic height of 0.15 kpc. For each source, the cosmic-ray density is calculated using a diffusion propagator with free escape at the halo boundaries of ±4 kpc. The injection spectra of the two populations differ: for supernova remnants, the index is 2.4 for protons and 2.24 for helium, with maximum energies of 68 and 468 TeV; for microquasars, the index is 2.0 with a cutoff at 6 PeV. Acceleration efficiencies are fitted to local measurements from DAMPE and LHAASO above 1 TeV. Secondary neutrinos and gamma rays are computed via hadronic collisions with a three-dimensional gas distribution, including atomic and molecular hydrogen.
Fitting the efficiencies yields values of about 10% for microquasar protons and 6% for supernova remnant protons, with uncertainties at the level of tenths of a percent. The predicted diffuse neutrino spectrum in the inner Galaxy agrees with IceCube templates, with supernova remnants dominating below 10 TeV and microquasars above, naturally explaining the observed spectral hardening. The diffuse gamma-ray flux, calculated with absorption on background radiation, reproduces LHAASO data in the inner and outer Galaxy. Above 100 TeV, the leptonic contribution is suppressed by the Klein–Nishina effect, leaving a pure hadronic background from microquasars. Spatial maps show that hot spots in the neutrino sky correspond not to individual accelerators but to regions of dense gas onto which the sea of cosmic rays is projected.
This work differs from neighboring studies in that it does not fit a single injection spectrum to the data but physically separates two source populations with different maximum energies and indices. This allows explaining the hardening of the diffuse spectrum above 10 TeV as a natural transition from soft supernova remnants to hard microquasars. The model provides a testable baseline background for point-source searches and links local cosmic-ray measurements to global diffuse emission, despite the stochasticity of nearby sources.
In the future, the model can be extended by adding anisotropic diffusion, fluctuations in source distribution, and more detailed interstellar gas maps. Accounting for recent active accelerators whose particles have not yet reached the Solar System but are already interacting with surrounding gas will help refine the contribution to diffuse neutrinos. Joint analysis of high-resolution neutrino and gamma-ray maps will help separate leptonic remnants below 100 TeV and characterize hadronic emission up to PeV energies.
The results will directly impact the search for point-like neutrino sources in the Galactic plane by providing a physically motivated background for IceCube, KM3NeT, and Baikal-GVD. They also provide a template for interpreting LHAASO diffuse gamma-ray data and for testing hypotheses about PeV accelerators.
Immediate next steps include incorporating anisotropic cosmic-ray transport and fluctuations in source distribution to obtain self-consistent templates. A systematic assessment of uncertainties from hadronic interaction models and the Galactic magnetic field is also planned.
This work directly addresses the unresolved problem of the origin of cosmic rays up to PeV energies and the contribution of different classes of Galactic accelerators. It also touches on the question of how to separate the diffuse background from point sources in multi-messenger observations, which remains a key challenge in neutrino astronomy.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The authors built a numerical model of the diffuse neutrino and gamma-ray emission from the Galaxy, separating the contributions of supernova remnants and microquasars. They calculated the spatial distribution of sources, injection spectra with different maximum energies and spectral indices, and fitted the acceleration efficiencies to the DAMPE and LHAASO data. The resulting neutrino spectrum agrees with IceCube, with supernova remnants dominating below 10 TeV and microquasars above.
Where its strength is
The model physically separates two populations of accelerators with different injection spectra, which naturally explains the observed hardening of the diffuse spectrum above 10 TeV. This provides a testable baseline for future multi-messenger observations.
Where it could go next
Worth trying
Why this may matter
Separating the contributions of different accelerator classes to the diffuse background is important for interpreting future data from IceCube-Gen2 and KM3NeT, as well as for searching for new source populations.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.60, against a usual 0.64. It looks like few have drilled nearby.
The proton acceleration efficiency of about 10% for microquasars means that each such object in its active phase injects energy into cosmic rays comparable to the Eddington luminosity for a black hole of 10 solar masses — approximately $10^{39}$ erg/s.