REVIEW
Galactic Microquasar and Supernova Remnants Imprinting on Diffuse Neutrino and Gamma-Ray Sky
High Energy Astrophysical Phenomena · Submitted 23 Aug 2026 · 41 references
Pith's verdict: A genuinely two-population template for Galactic diffuse neutrinos and gamma rays, with a plausible microquasar takeover above ~10 TeV that is not yet independently established because the key efficiencies are fitted to local CR data.
T0 · AI review
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Referee report
The paper
The paper claims
The paper claims that Milky Way diffuse neutrinos and gamma rays come from supernova remnants below about 10 TeV and microquasars above, in a model anchored to local cosmic-ray data that matches IceCube and LHAASO.
The reading
What carries the argument
The load-bearing mechanism is a two-population cosmic-ray injection and transport model whose line-of-sight emission integral turns the population crossover into observable spectra. Microquasars are stellar-mass black holes with relativistic jets, treated here as a separate source class from supernova remnants. The central object is the spatial overlap integral $X(\Omega,E_p)=\int_0^\infty ds\, n_{\rm gas}(r)\,n_p(E_p,r)$ that multiplies the CR density at each point by the interstellar target gas density (atomic and molecular hydrogen plus heavier elements) and integrates it along each line of sight; feeding this through the Kamae et al. pion-decay yields converts CR density into neutrino and gamma-ray emissivity. CRs are propagated with an isotropic diffusion propagator with free-escape halo boundaries at $\pm4$ kpc, implemented by image charges, so each source contributes a smoothed cosmic-ray sea. What carries the argument is the crossover energy: the soft, low-cutoff SNR injection (with a diffusion-softened index $s_{\rm cr}\approx\Gamma-\tfrac13$) dominates low energies, while the hard, 6 PeV-cutoff microquasar injection overtakes it above about 10 TeV, producing the spectral hardening without any extra fitted component.
Extended reading notes
Core claim
The paper's central claim is that escaped cosmic rays from two Galactic source populations leave distinct, energy-ordered imprints on the diffuse neutrino and gamma-ray sky, and that this decomposition can be calibrated without free tuning of the high-energy sky. Supernova remnants inject soft spectra (proton index 2.40, helium index 2.24, cutoffs near 68 and 468 TeV), while microquasars inject hard spectra (index 2.0 up to 6 PeV), with the four CR luminosities fixed by fitting to DAMPE and LHAASO local data. Propagating these populations through the Galaxy and folding them onto 3D gas maps gives a neutrino spectrum whose sub-TeV-to-10-TeV range is SNR-dominated and whose higher-energy range is microquasar-dominated; the predicted flux brackets the IceCube 12-year Galactic diffuse template and the LHAASO diffuse gamma-ray measurements. In the gamma-ray band, the model leaves a residual excess below about 100 TeV attributed to leptonic inverse-Compton emission and faint unresolved sources, while above 100 TeV the sky is predicted to be a clean hadronic baseline. The paper therefore claims the observed spectral hardening is a natural prediction of the population crossover, not evidence for a new spectral component.
Load-bearing premise
That the local cosmic-ray flux measured at Earth above 1 TeV is a faithful normalization anchor for the entire Galaxy, so efficiencies fitted to local data can be extrapolated to the whole source population using a modeled spatial distribution.
Editorial extensions
If this is right
- Below about 10 TeV, the diffuse neutrino and gamma-ray emission is dominated by cosmic rays escaped from supernova remnants; above that energy, microquasars take over.
- The predicted neutrino spectrum sits below the IceCube template fits at the highest energies, leaving room for unresolved point-like sources and nearby active accelerators on top of the hadronic baseline.
- In gamma rays, the model predicts a mostly hadronic sky above about 100 TeV, where inverse-Compton emission is suppressed by Klein-Nishina effects, so LHAASO's high-energy photons map the PeV cosmic-ray sea directly.
- Neutrino hot spots in the Galactic plane need not mark individual accelerators; they trace where the accumulated cosmic-ray sea overlaps dense interstellar gas.
- The spectral hardening around 10 TeV is a natural consequence of the population crossover, not an additional fitted ingredient.
Reading between the lines
- If the population-crossover picture is right, a future measurement that resolves the hardening energy of the diffuse neutrino spectrum would act as a calorimeter of the relative cosmic-ray output of microquasar versus supernova remnant populations, independent of local flux normalization assumptions.
- The same local-anchoring and spatial-extrapolation recipe could be applied to other candidate accelerators, such as star-forming regions or pulsar halos; each would imprint a characteristic crossover energy and could be distinguished from the SNR-plus-microquasar baseline in high-statistics neutrino maps.
- The sub-100 TeV gamma-ray excess attributed to inverse-Compton emission and unresolved sources is testable: because neutrinos are unattenuated, a joint gamma-ray and neutrino analysis of the same sky region should reveal whether that residual tracks known lepton-injection sites, or whether the hadronic baseline itself needs revision.
Original abstract
Recent detections of Galactic diffuse neutrinos by IceCube and $\gamma$-rays by LHAASO offer direct probes into the origin of Galactic cosmic rays. Conventional diffuse templates typically assume a single cosmic-ray injection spectrum across a wide energy range, without accounting for independent contributions from distinct accelerator populations. Here, we present a numerical framework that models Galactic diffuse neutrino and $\gamma$-ray emission that incorporates contributions from both microquasar and supernova remnant populations. By anchoring CR injection to local observations and utilizing high-resolution 3D target gas distributions, our model suggests multi-population contributions to the diffuse sky: escaped cosmic rays from supernova remnants dominate below $\sim10\text{ TeV}$, while those from microquasars become the primary driver at higher energies. Our predicted neutrino flux agrees well with the recent 12-year IceCube measurements, establishing a physically motivated baseline for the diffuse hadronic background while leaving room for unresolved point-like sources. This flexible framework provides testable predictions for current and future multi-messenger observatories, accommodating diverse accelerator populations and updated observational constraints.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
Recent detections of Galactic diffuse neutrinos by IceCube and $\gamma$-rays by LHAASO offer direct probes into the origin of Galactic cosmic rays. Conventional diffuse templates typically assume a single cosmic-ray injection spectrum across a wide energy range, without accounting for independent contributions from distinct accelerator populations. Here, we present a numerical framework that models Galactic diffuse neutrino and $\gamma$-ray emission that incorporates contributions from both microquasar and supernova remnant populations. By anchoring CR injection to local observations and utilizing high-resolution 3D target gas distributions, our model suggests multi-population contributions to the diffuse sky: escaped cosmic rays from supernova remnants dominate below $\sim10\text{ TeV}$, while those from microquasars become the primary driver at higher energies. Our predicted neutrino flux agrees well with the recent 12-year IceCube measurements, establishing a physically motivated baseline for the diffuse hadronic background while leaving room for unresolved point-like sources. This flexible framework provides testable predictions for current and future multi-messenger observatories, accommodating diverse accelerator populations and updated observational constraints.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Recent detections of Galactic diffuse neutrinos by IceCube and $\gamma$-rays by LHAASO offer direct probes into the origin of Galactic cosmic rays. | background 1.00 | 0.05 | 0.03 | asserted 0.98 |
| s1 | Conventional diffuse templates typically assume a single cosmic-ray injection spectrum across a wide energy range, without accounting for independent contributions from distinct accelerator populations. | gap 0.89 | 0.05 | 0.02 | asserted 1.00 |
| s2 | Here, we present a numerical framework that models Galactic diffuse neutrino and $\gamma$-ray emission that incorporates contributions from both microquasar and supernova remnant populations. | contribution 0.88 | 0.94 | 0.12 | asserted 1.00 |
| s3 | By anchoring CR injection to local observations and utilizing high-resolution 3D target gas distributions, our model suggests multi-population contributions to the diffuse sky: escaped cosmic rays from supernova remnants dominate below $\sim10\text{ TeV}$, while those from microquasars become the primary driver at higher energies. | result 0.96 | 0.92 | 0.86 | hedged possibility 1.00 |
| s4 | Our predicted neutrino flux agrees well with the recent 12-year IceCube measurements, establishing a physically motivated baseline for the diffuse hadronic background while leaving room for unresolved point-like sources. | result 0.87 | 0.90 | 0.13 | asserted 0.96 |
| s5 | This flexible framework provides testable predictions for current and future multi-messenger observatories, accommodating diverse accelerator populations and updated observational constraints. | future work 0.61 | 0.51 | 0.08 | asserted 0.95 |
What was examined, and what was not
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Figures
Figures reproduced from arXiv:2608.22374 by the authors.
References
Discussion
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