{"id":"85b2e65f-3134-4673-9633-d9212fa7dbc9","arxiv_id":"2504.18796","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":8,"one_line_summary":"GALPROP cosmic-ray propagation models match the large-scale TeV gamma-ray emission seen by H.E.S.S. once catalogued and unresolved sources are accounted for.","lead":"A PhD thesis uses the GALPROP code to model cosmic-ray propagation and gamma-ray emission in the Milky Way, and compares the predictions to the H.E.S.S. Galactic plane survey in the TeV band. The study quantifies how much the predicted diffuse TeV gamma-ray sky changes when key Galactic inputs are varied.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The TeV–PeV agreement claim is anchored to an HGPS residual that the paper itself labels a lower limit, with an unresolved-source add-back spanning 13–60%; the comparison is too underdetermined to support the headline claim.","rationale":"The reader's rationale already flags lower-limit HGPS fluxes and the wide unresolved-source fraction, but their weakest_assumption emphasises the isotropic, homogeneous diffusion extrapolation to PeV. In my reading, the more load-bearing problem is the comparison target itself: Section 3.4.1 admits the HGPS large-scale flux is only a lower limit, and the unresolved-source correction spans 13–60%. A one-sided observational quantity with a factor-of-several additive uncertainty is too weak to support the stated agreement claim without a quantitative fit. The diffusion-coefficient extrapolation is a real secondary uncertainty, but it is a model uncertainty rather than an immediate logical gap in the comparison. Because the HGPS concern is addressable by reanalysis and does not by itself disprove the model, the CONDITIONAL verdict is appropriate and no verdict adjustment is needed.","tokens_in":59734,"tokens_out":10162,"duration_ms":115856,"concrete_test":"On the public HGPS R_c=0.2° flux maps, reproduce the Sec. 4.1 sliding-window longitudinal profile after masking all 78 HGPS sources. Compute the profile for (i) the published lower-limit maps, (ii) the lower-limit flux with the median +15% correction inferred from the FoV-background reanalysis of Abdalla et al. (2021), and (iii) unresolved-source contributions of 13% and 60% added to the residual. Compare each resulting band to the SA50 GALPROP profile over -60° < l < 30° using a chi-square or residual test. If the GALPROP curve is inside the band in case (i) but outside the band in case (ii) or (iii), the claimed agreement depends on the lower-limit and unresolved-source treatment.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that GALPROP agrees with H.E.S.S. in the TeV regime depends on treating the large-scale residual of the HGPS as a measured diffuse flux. Section 3.4.1 explicitly states that the adaptive-ring background method (Sec. 3.2.3) over-estimates the CR background because it can include large-scale gamma-ray emission in the off regions, so the public HGPS flux maps are only lower limits on the true large-scale emission. Section 3.4 further notes that the large-scale component was not detected at the 5σ level. The comparison pipeline in Chapter 4 then masks the 78 catalogued sources and adds an unresolved-source estimate, whose literature range is 13–60% of the large-scale flux (Sec. 3.4.1, Sec. 4.3.2). A one-sided lower limit plus a factor-of-several additive correction can be declared broadly compatible with a model even when the model is biased high or low by a comparable amount. The thesis does not report a quantitative goodness-of-fit against the corrected diffuse intensity, so the abstract's agreement statement overstates what the HGPS comparison actually establishes. The LHAASO PeV comparison may be more constraining, but the HGPS leg of the claim is not established to the precision implied by 'agree with observations'.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This thesis-style manuscript presents simulations of Galactic cosmic-ray (CR) transport with GALPROP, computing gamma-ray emission from 1 TeV to 1 PeV. Diffusion and injection parameters are fitted to local CR spectra from AMS-02 and Voyager, and the resulting predictions are compared with the H.E.S.S. Galactic plane survey (HGPS) after masking 78 catalogued sources, applying an integration beam, and adding an unresolved-source contribution. The manuscript also quantifies the modelling variation induced by choices of CR source distribution, interstellar radiation field, and Galactic magnetic field, and investigates time-dependent CR injection and the resulting variability of the TeV electron flux at Earth. The central claim is that GALPROP predictions are broadly compatible with the HGPS large-scale emission in the TeV regime and agree with LHAASO observations in the PeV regime, extending the validated energy range of GALPROP. The final chapter discusses the detectability of the diffuse Galactic emission with CTA.","tokens_in":60081,"tokens_out":7802,"duration_ms":82664,"significance":"If the agreement claim is established, the work would extend GALPROP's demonstrated accuracy into the TeV–PeV regime and would provide a useful reference for CTA background modelling. The manuscript has several genuine strengths: the optimisation parameters are reported in Table 2.4, the comparisons to HGPS and LHAASO use data not included in the fit (an external benchmark), the sliding-window analysis is explicitly tested for robustness to window width and spacing, and the systematic exploration of ISRF, source-distribution, GMF, and stochastic source-placement uncertainties is a useful contribution. The time-dependent study of TeV electron variability is also physically interesting. However, the support for the headline agreement claim is currently under-quantified, and the HGPS leg in particular rests on a lower-limit dataset corrected by an unresolved-source estimate that spans a factor of several.","major_comments":[{"comment":"The HGPS comparison is the load-bearing part of the TeV agreement claim, but the observed quantity is a one-sided lower limit. Section 3.4.1 explicitly states that the adaptive-ring background method can include the large-scale gamma-ray emission in the off regions and that 'the HGPS flux can only be considered as a lower limit on the true large-scale gamma-ray emission'; Section 3.4 adds that the large-scale component was not detected at the 5σ level. After masking the 78 catalogued sources and adding an unresolved-source estimate ranging from 13% to 60% of the large-scale flux, the manuscript concludes 'broad compatibility' but reports no quantitative goodness-of-fit (no chi-square, residual RMS, or coverage fraction) for the corrected intensity profile. With a lower limit plus a factor-of-several additive correction, a model can be declared compatible over a wide range of model bias. I request a quantitative residual analysis against the corrected profile, with the full systematic band propagated, or a softened statement of the TeV agreement in the abstract and conclusion.","section":"§3.4.1, §4.3.1–4.3.2"},{"comment":"The unresolved-source fraction is a dominant systematic: the text cites Steppa and Egberts (2020) at 13% and Cataldo et al. (2020) at 60% of the large-scale flux. The manuscript does not show how the GALPROP-to-HGPS comparison changes across this range, nor does it state which value is adopted for the final agreement claim. Because the add-back directly shifts the data by as much as a factor of ~1.7 between the low and high estimates, the agreement could be an artifact of the chosen value. The authors should display the sliding-window residual for at least the 13%, ~35%, and 60% cases, or explicitly justify a single adopted value and demonstrate that the conclusion is insensitive to it.","section":"§4.3.2"},{"comment":"The diffusion coefficient is assumed isotropic, homogeneous, and a single power law in rigidity, D(E) = beta D0 (rho/4 GV)^delta, with delta ≈ 0.34–0.35 fitted to CR spectra that are most constraining at GeV–TeV energies. The manuscript's PeV claim relies on extrapolating this parametrisation to PeV rigidities, where the gyroradius approaches the Galactic disk thickness and transport assumptions can change. The abstract asserts agreement with LHAASO, but the provided text does not quantify the constraining power of that comparison (e.g., what range of D0 and delta is excluded by the LHAASO data, or the systematic uncertainty from the assumed homogeneous isotropic diffusion). I ask the authors to state explicitly what the LHAASO comparison tests and to present the resulting allowed parameter range, or to qualify the PeV agreement claim accordingly.","section":"§2.7.1, Eq. (2.13)"}],"minor_comments":[{"comment":"The phrase 'agree with observations of the diffuse gamma rays in the TeV regime by H.E.S.S.' overstates the result given the caveats in §3.4.1 and §4.3.2; a more precise wording such as 'broadly consistent with the HGPS large-scale emission after source masking and unresolved-source corrections' would match the analysis actually presented.","section":"Abstract"},{"comment":"The lower-limit nature of the HGPS flux is stated in §3.4.1 but is not restated when the comparison pipeline is built in Chapter 4; readers of the comparison figures in Chapter 5 may not realize the observed profile is biased low. A brief reminder sentence at the start of §4.3 would improve clarity.","section":"§3.4.1 / Chapter 4"},{"comment":"The residual from applying the telescopic beam to GALPROP can reach 10% for features smaller than 0.2°, and the text states the effect on the sliding-window profile is 'on the order of one part in ten thousand'. Showing the maximum residual over the longitudinal profile rather than a single descriptive value would make this robustness statement more transparent.","section":"§4.2.2"},{"comment":"The cooling-distance equations mix D0 in cm^2 s^-1 with distances in parsecs and times in years without an explicit unit conversion; a brief note on the conversion factors used would prevent confusion for readers implementing these estimates.","section":"§2.2.4, Eqs. (2.44)–(2.47)"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a PhD-thesis compilation containing two peer-reviewed papers; the arXiv version presents the complete thesis with the published chapters included. The main added value over the published papers is the explicit HGPS comparison pipeline and the systematic variation study. My review treats the full compilation as the manuscript. The central problem is not the transport modelling itself but the unquantified relationship between the observed HGPS lower limit plus a widely varying unresolved-source add-back and the claimed 'agreement'. The issues are fixable by adding a quantitative residual analysis and by either propagating the 13–60% range or clearly justifying a single value, and by tempering the abstract's wording; I therefore recommend major revision rather than rejection."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a PhD thesis with two embedded peer-reviewed papers (Marinos et al. 2023, 2025). The genuinely new and useful parts are the first systematic quantification of how TeV–PeV diffuse gamma-ray predictions shift when you change the CR source distribution, ISRF, or GMF—including stochastic source placement—and the first comparison of a CR transport code to the HGPS large-scale emission. The propagation setup is standard and transparent: parameters are tabulated, the model is normalised to AMS-02 and Voyager, and the source masks and sliding-window method are described in enough detail to reproduce. The time-dependent variability result (TeV electron flux at Earth varying by more than a factor of ten over a few Myr) is a solid, citable addition.\n\nThe soft spot is the abstract's claim that the models 'agree with observations' from HESS and LHAASO. The HGPS leg is anchored to a lower-limit flux map: the adaptive ring background method can absorb large-scale emission into the CR background, and the large-scale component was not detected at 5σ. After masking 78 catalogued sources, the analysis adds an unresolved-source contribution whose literature range is 13–60%. A one-sided lower limit plus a factor-of-several additive correction can look 'broadly compatible' with almost any model within that band. The thesis itself uses the phrase 'broadly compatible', which is about as strong as the data support, but the abstract overstates it. The LHAASO comparison may be more constraining, yet the thesis presents no quantitative goodness-of-fit for either leg, so the actual strength of the PeV claim is hard to evaluate.\n\nThe isotropic, homogeneous diffusion assumption is a standard approximation in GALPROP and the thesis is honest about it—a limitation, not an error. The lack of configuration files is a minor reproducibility issue since GALPROP itself is public.\n\nWho gets value: CR propagation modelers, TeV/PeV observers planning CTA diffuse-background analyses, and anyone working on Galactic diffuse emission. The modelling-variation framework is worth citing. This deserves a serious referee: the embedded papers are already peer-reviewed, and the thesis adds full methodological detail. My recommendation is to send it out, with the referee asked to require either a quantitative comparison metric for the HGPS/LHAASO legs or a revised abstract that says 'not excluded' for the TeV leg. As written, the headline claim is stronger than the data justify.","headline":"Solid thesis with two peer-reviewed papers inside; the HGPS 'agreement' claim outruns the lower-limit data, but the modelling-variation and time-variability results are genuinely useful.","tokens_in":60628,"tokens_out":5270,"would_cite":true,"duration_ms":55194,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This thesis shows that GALPROP cosmic-ray transport models, after masking catalogued sources and adding unresolved ones, reproduce the Milky Way's diffuse gamma-ray emission from TeV to PeV energies.","keywords":["cosmic rays","gamma-ray astronomy","diffuse emission","GALPROP","Galactic cosmic-ray transport","TeV gamma rays","PeV gamma rays","CTA"],"falsifier":"A decisive test would be a clean measurement of the diffuse gamma-ray spectrum between 10 TeV and 1 PeV in a region with few discrete sources, compared directly with the GALPROP prediction at the fitted $\\delta\\sim0.34$; if the observed flux falls outside the model's factor-of-two magnetic-field band, or shows a spectral break the model cannot produce, the claimed TeV-PeV accuracy fails.","tokens_in":59481,"feed_emoji":"🌌","tokens_out":6666,"duration_ms":62160,"temperature":0.7,"pith_summary":"The paper tries to establish that the standard GALPROP model of cosmic-ray transport, tuned to GeV-scale local measurements, continues to predict the Milky Way's diffuse gamma-ray emission correctly at TeV and PeV energies. It does this by comparing simulated gamma-ray maps to the H.E.S.S. Galactic plane survey after masking the 78 catalogued sources and adding estimates of unresolved sources, and to LHAASO's PeV measurements. The author also quantifies, for the first time, how much the TeV predictions vary with model choices such as source distribution, interstellar radiation field, magnetic field, and stochastic source placement, finding that the magnetic field changes the large-scale emission by about a factor of two above 1 TeV. If right, the result makes GALPROP a reliable diffuse background model for current and next-generation TeV observatories and narrows where cosmic-ray sources sit in the Galaxy.","feed_headline":"GALPROP diffuse gamma-ray models hold up to TeV-PeV data","feed_subtitle":"Simulated cosmic-ray diffusion across the Milky Way now matches diffuse gamma-ray observations from TeV to PeV energies.","key_machinery":"The central object is GALPROP's numerical solution of the three-dimensional cosmic-ray transport equation, with an isotropic, homogeneous spatial diffusion coefficient $D_{xx}(R)=\\beta D_0(R/4\\,\\mathrm{GV})^{\\delta}$ plus diffusive reacceleration. This diffusion law, with the index $\\delta$ fitted to local cosmic-ray spectra and taking values near 0.34 to 0.35 for the source distributions considered, is what converts assumed source, gas, radiation-field, and magnetic-field inputs into cosmic-ray densities and hence gamma-ray skymaps. The comparison machinery is a sliding-window longitudinal profile applied identically to simulated and observed maps, with the HGPS sources masked using the survey's own source model and an unresolved-source fraction added to represent what the telescope cannot resolve.","core_discovery":"GALPROP's steady-state, diffusion-plus-reacceleration models of Galactic cosmic-ray transport, with a rigidity-dependent diffusion coefficient fitted to local cosmic-ray data, produce diffuse gamma-ray skies that are broadly compatible with the HGPS large-scale emission once catalogued sources are masked and an unresolved-source component is included. The same models match LHAASO's diffuse PeV observations, so the demonstrated accuracy extends from the GeV regime into the TeV-PeV regime. At 1 TeV, electrons contribute roughly half of the large-scale emission; above 1 TeV the choice of Galactic magnetic field model changes the predicted emission by about a factor of two; and in time-dependent runs the electron flux at Earth above 1 TeV varies by more than a factor of ten over a few million years. The proposed CTA Galactic plane survey should be sensitive enough to detect the large-scale diffuse TeV emission.","pith_inferences":["The author leaves implicit that the same source-masking and sliding-window comparison could be applied to other air-shower observatories with wider sky coverage, providing a cross-check of the claimed TeV-PeV agreement at intermediate latitudes and longitudes.","The narrow spread in fitted diffusion indices across the five source distributions suggests the TeV-PeV agreement is not strongly sensitive to the spiral-arm versus disk decomposition; a testable extension would compare the model's outer-Galaxy longitude profile to observations, where the source distribution matters most.","If the predicted multi-TeV electron variability is real, searches for nearby, recently active cosmic-ray accelerators could target the corresponding gamma-ray hotspots on million-year timescales, a consequence the paper does not chase.","The magnetic-field sensitivity above 1 TeV implies that future diffuse TeV surveys, combined with an independently pinned-down unresolved-source fraction, could be used to discriminate between Galactic magnetic-field models."],"forward_implications":["GALPROP can serve as a diffuse background model for TeV-PeV gamma-ray analyses, in the same role it already plays at GeV energies for Fermi-LAT.","Because electrons contribute about half of the 1 TeV large-scale emission, TeV source studies must account for inverse-Compton and bremsstrahlung emission, not only pion decay from hadronic interactions.","The factor-of-two sensitivity to the Galactic magnetic field above 1 TeV means magnetic-field uncertainty is a leading limitation on diffuse TeV predictions, not just the source distribution.","Time variability of the multi-TeV electron flux at Earth implies that single-epoch electron measurements must be interpreted cautiously.","The planned CTA Galactic plane survey will be sensitive enough to observe the large-scale diffuse TeV gamma-ray emission directly."],"supporting_citations":[{"why":"Foundational GALPROP paper; supplies the transport-equation solver and gamma-ray production formalism used for all predictions.","marker":"Moskalenko and Strong, 1998"},{"why":"Companion paper defining the GALPROP framework and its treatment of Galactic sources, gas, and diffuse emission.","marker":"Strong and Moskalenko, 1998"},{"why":"Provides the HGPS flux maps, source catalogue, source-masking recipe, and sliding-window large-scale emission analysis that the comparison is built on.","marker":"Abdalla et al., 2018e"},{"why":"Supplies the interstellar radiation field models and the parameter-optimisation procedure used to fit diffusion and injection parameters.","marker":"Porter et al., 2017"},{"why":"Provides the three-dimensional gas density model used as a propagation input for the simulations.","marker":"Jóhannesson et al., 2018"},{"why":"Compiles the local cosmic-ray spectra used to normalise and optimise the propagation parameters.","marker":"Jóhannesson et al., 2019"},{"why":"One of the unresolved-source fraction estimates added to the masked HGPS before comparing with the diffuse predictions.","marker":"Steppa and Egberts 2020"},{"why":"The other unresolved-source estimate, bracketing the plausible contribution of unresolved sources to the large-scale emission.","marker":"Cataldo et al. 2020"},{"why":"LHAASO measurement of diffuse gamma rays at PeV energies that the models are claimed to agree with.","marker":"Cao et al. 2023"}],"fun_headline_variants":["GALPROP cosmic-ray models match gamma-ray data to PeV","Diffuse gamma-ray sky: GALPROP extends to TeV-PeV regime","GALPROP validated against H.E.S.S. and LHAASO diffuse emission","TeV-PeV diffuse gamma rays: GALPROP predictions confirmed","Cosmic-ray transport in Galaxy matches observed diffuse gamma rays"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that cosmic-ray transport in the Milky Way is smooth and direction-independent, with a single energy-dependent diffusion coefficient that remains valid up to PeV energies.","fun_headline_variants_meta":{"raw":{"variants":["GALPROP cosmic-ray models match gamma-ray data to PeV","Diffuse gamma-ray sky: GALPROP extends to TeV-PeV regime","GALPROP validated against H.E.S.S. and LHAASO diffuse emission","TeV-PeV diffuse gamma rays: GALPROP predictions confirmed","Cosmic-ray transport in Galaxy matches observed diffuse gamma rays"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000281,"raw_usage":{"total_tokens":1735,"prompt_tokens":1086,"completion_tokens":649,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":702,"completion_tokens_details":{"reasoning_tokens":551}},"tokens_in":702,"tokens_out":649,"duration_ms":6075,"temperature":1.0,"reasoning_tokens":551,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-16T10:08:40.117243+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A decisive test would be a clean measurement of the diffuse gamma-ray spectrum between 10 TeV and 1 PeV in a region with few discrete sources, compared directly with the GALPROP prediction at the fitted $\\delta\\sim0.34$; if the observed flux falls outside the model's factor-of-two magnetic-field band, or shows a spectral break the model cannot produce, the claimed TeV-PeV accuracy fails.","supporting_citations":[{"cited_title":"Propagation of Cosmic-Ray Nucleons in the Galaxy","cited_arxiv_id":null,"evidence_quote":"Companion paper defining the GALPROP framework and its treatment of Galactic sources, gas, and diffuse emission."},{"cited_title":"Modelling the Galactic Very-High-Energy Gamma- Ray Source Population","cited_arxiv_id":null,"evidence_quote":"One of the unresolved-source fraction estimates added to the masked HGPS before comparing with the diffuse predictions."},{"cited_title":"The TeV Gamma-Ray Luminosity of the Milky Way and the Contribution of H.E.S.S. Unresolved Sources to Very High Energy Diffuse Emission","cited_arxiv_id":null,"evidence_quote":"The other unresolved-source estimate, bracketing the plausible contribution of unresolved sources to the large-scale emission."},{"cited_title":"MeasurementofUltra-High-EnergyDif- fuse Gamma-Ray Emission of the Galactic Plane from 10TeV to 1PeV with LHAASO- KM2A","cited_arxiv_id":null,"evidence_quote":"LHAASO measurement of diffuse gamma rays at PeV energies that the models are claimed to agree with."}],"review_version":1}