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arxiv: 2604.22621 · v1 · submitted 2026-04-24 · 🌌 astro-ph.HE

Recognition: unknown

Ultra-high-energy γ-ray imprints from PeV particles accelerated by supernova remnants

A. Inventar, A.J. Dong, A. Neronov, A. Raza, A. S\'aiz, A.V. Bukevich, B.B. Zhang, B. Gao, B. Liu, B.N. Xu, B.Q. Ma, B.T. Zhang, B.W. Hou, B.Y. Zhu, B.Z. Dai, B. Zhou, C.F. Feng, C.G. Zhu, Cheng Li, C. Hou, C. Huang, C. Liu, C.M. Cai, C.N. Tong, Cong Li, C. Wang, C.W. Yang, C.Y. Ren, C.Y. Wu, C.Y. Xu, C.Y. Yang, C. Zhang, Danzengluobu, D. Bastieri, D.B. Liu, D.H. Huang, D.H. Wang, D.H. Yan, D. Khangulyan, D. Kuleshov, D. Li, D. Liu, D.L. Xu, D.M. Wei, D. Qu, D. Ruffolo, D.R. Xiong, D. Savchenko, D. Semikoz, D.X. Sun, D.X. Xiao, D.Y. Peng, E.S. Chen, E.W. Liang, F. Aharonian, F.F. Yang, F.L. Guo, F. Li, F.R. Zhu, F.W. Shu, F. Zheng, G.B. Mou, G. Giacinti, G.H. Chen, G.H. Gong, G.M. Xiang, G.W. Wang, G. Xiao, H.B. Hu, H.B. Jiang, H.B. Li, H.B. Tan, H.C. Li, H.C. Song, H.D. Xing, H.D. Zeng, H. Feng, H.G. Wang, H.H. He, H.K. Chen, H.K. Lv, H.L. Dai, H. Liu, H.M. Zhang, H.N. He, H.R. Wu, H. Sun, H.Y. Jia, H. Yue, H.Y. Zhang, H. Zhang, H. Zhou, H. Zhu, I. Karpikov, I.O. Maliy, J. Blunier, J. Chang, J.C. Qi, J.C. Wang, J. Fang, J.F. Chang, J. Guo, J.H. Fan, J.H. Fang, Jian Li, Jie Li, J.J. Huang, J.J. Qin, J.J. Wei, J.J. Xia, J. Liu, J.L. Liu, J.L. Zhang, J.N. Zhou, J.R. Liu, J.R. Mao, J. Takata, J. Xia, J.X. Sun, J.Y. He, J.Y. Zhang, J. Zhao, Kai Wang, K.C.Y. Ng, K. Fang, K.J. Guo, K. Jia, K. Jiang, K.J. Zhu, K.K. Duan, K. Kurinov, K. Li, K. Wang, L.F. Chen, L. Feng, L.H. Wan, Liang Chen, Li Zhang, L.J. Ou, L. Li, L.L. Ma, L.L. Yang, L. Nie, Long Chen, L.P. Wang, L.Q. Yin, L.S. Geng, L. Shao, L. Xue, L.Y. Wang, L. Zhao, L.Z. Zhao, M. Hasan, M.H. Gu, M.J. Chen, M. Jin, M.J. Yang, M.L. Chen, M.M. Ge, M.M. Kang, M.Y. Cui, M.Y. Liu, M.Y. Ni, M.Y. Qi, M. Zha, M. Zhou, N. Cheng, N.H. Tabasam, N. Yin, O.A. Hannuksela, O. Shchegolev, P.F. Zhang, P.H.T. Tam, P. Pattarakijwanich, P. Zhou, Q.B. Gou, Q. Gao, Q.H. Chen, Q. Luo, Q.N. Sun, Q.W. Tang, Q.W. Wu, Q.Y. Cheng, Q. Yuan, R.F. Xu, R.L. Li, R.P. Han, R. Tang, R. Wang, R.X. Xu, R.Y. Liu, R. Zhang, R. Zhou, R.Z. Yang, S. Chen, S.C. Hu, S.D. Li, S. Gabici, S.H. Chen, S. Hern\'andez-Cadena, S.H. Feng, S.J. Lin, S. Kaci, S.M. Liu, S.P. Zhao, S.Q. Xi, S.R. Zhang, S.S. Weng, S.S. Xu, S.S. Zhang, S.W. Cui, S. Wu, S.Y. Zhang, S.Z. Chen, T.C. Zheng, T.L. Chen, T.T. Ge, T. Wen, T.X. Zeng, T. Yan, T.Y. Li, W. Bian, W. Gao, W.K. Gao, W. Liu, W.L. Li, W.L. Xu, W. Mitthumsiri, W. Wang, W.W. Tian, W.X. Yang, W.Y. Cao, W.Y. Zhang, W. Zeng, W. Zhang, X.A. Ye, X.B. Chen, X.D. Sheng, X.F. Wu, X.G. Wang, X.H. Cui, X.H. Ma, X. Hou, X.H. You, X.H. Zhao, X.J. Bi, X.J. Chen, X.J. Wang, X.L. Guo, X.L. Huang, X. Liu, X.L. Ji, X.N. Sun, X.P. Chen, X.P. Zhang, X.Q. Dong, X.R. Li, X.T. Feng, X.T. Huang, X.T. Zeng, X.W. Jiang, X.X. Zhou, X.Y. He, X.Y. Huang, X.Y. Wang, X. Zhang, X. Zuo (The LHAASO Collaboration), Y. Chen, Y.C. Zou, Y.D. Cheng, Y.D. Cui, Y.D. Wang, Y. Feng, Y.F. Liang, Y.F. Xiao, Y. He, Y. Huang, Yi Zhang, Y.J. Bi, Y.J. Wei, Y.L. Feng, Y. Li, Y. Liu, Y. Luo, Y.L. Xin, Y. Mizuno, Y.N. Liu, Yong Zhang, Y.Q. Guo, Y.Q. Lou, Y. Su, Y.S. Wu, Yu.V. Stenkin, Y. Wang, Y.W. Bao, Y.X. Bai, Y.X. Diao, Y. Xing, Y.Y. Cai, Y.Y. Guo, Y.Y. Huang, Y.Z. Fan, Y.Z. Shen, Z.B. Sun, Z.B. Tang, Z.D. Shi, Z.G. Dai, Z.G. Yao, Zhe Cao, Zhe Li, Zhen Cao, Zheng Wang, Zhuo Li, Z.H. Wang, Z.H. Yang, Z.H. Zhao, Z.J. Jiang, Z. Min, Z.P. Zhang, Z.W. Ou, Z.X. Wang, Z.Y. Pei, Z.Y. You

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Pith reviewed 2026-05-08 10:19 UTC · model grok-4.3

classification 🌌 astro-ph.HE
keywords supernova remnantscosmic raysgamma raysPeV energiesmolecular cloudshadronic interactionsLHAASO observationsultra-high-energy emission
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The pith

Gamma-ray observations from two supernova remnants indicate cosmic ray acceleration to PeV energies through hadronic interactions with molecular clouds.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper presents LHAASO observations of very-high-energy gamma rays reaching hundreds of TeV from the middle-aged shell-type supernova remnants G150.3+4.5 and gamma-Cygni. Both sources exhibit two or three distinct morphological and spectral components with convex shapes, where the highest-energy emission is more compact than the lower-energy parts. The compact high-energy components align spatially with molecular clouds at comparable distances, and there are no strong pulsar wind nebula signatures. This leads to the conclusion that the ultra-high-energy gamma rays arise from collisions between cosmic ray protons accelerated to PeV energies and the clouds, rather than leptonic processes. Such findings align with longstanding models in which supernova remnants accelerate particles to the knee of the cosmic ray spectrum near 3 PeV during their early evolutionary stages.

Core claim

The highest-energy gamma-ray emission components in G150.3+4.5 and gamma-Cygni are produced by hadronic cosmic rays up to PeV energies colliding with molecular clouds at similar distances, as shown by the differences in spatial extension between components and the absence of pulsar wind nebulae; these results match predictions that PeV particles accelerated near the end of the free-expansion phase can illuminate nearby clouds to generate strong gamma-ray emission.

What carries the argument

The two (or three) distinct morphological/spectral components with convex spectral shapes, in which the high-energy component is less extended and spatially associated with molecular clouds, isolating the hadronic PeV contribution from lower-energy emission.

If this is right

  • PeV particles are accelerated near the end of the free-expansion phase of supernova remnant evolution.
  • Nearby molecular clouds can be illuminated by these PeV cosmic rays to produce detectable ultra-high-energy gamma-ray emission.
  • Supernova remnants remain efficient accelerators of particles beyond PeV energies in at least some cases.
  • The observed convex spectra and morphological separation support hadronic origins over leptonic alternatives for the highest-energy emission.
  • These detections provide direct evidence compatible with supernova remnants as the main sources of galactic cosmic rays up to the spectral knee.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If the same pattern appears in additional supernova remnants, it would strengthen the case that PeV acceleration occurs routinely in middle-aged shells.
  • The separation of components by energy and size offers a practical method for distinguishing hadronic from leptonic gamma-ray sources in other objects.
  • Future multi-wavelength campaigns targeting molecular cloud interfaces with supernova remnants could test the timing of peak acceleration relative to evolutionary phase.
  • The results imply that undetected or weak pulsar contributions do not dominate the highest-energy emission in these particular sources.

Load-bearing premise

The high-energy morphological and spectral component must be hadronic emission from molecular clouds at the same distance and not dominated by undetected leptonic processes or weak pulsar wind nebulae.

What would settle it

Discovery of a pulsar or pulsar wind nebula inside either remnant that matches the position, spectrum, and extension of the high-energy gamma-ray component, or distance measurements placing the associated molecular clouds at a significantly different distance from the supernova remnant.

read the original abstract

The quest for the origin of cosmic ray (CRs) is a fundamental issue in astrophysics. Shocks of supernova remnants (SNRs) have been considered as the dominant contributors to Galactic CRs below the spectral knee near $\sim 3$ petaelectronvolt (PeV). Whether SNRs are efficient accelerators of particles beyond PeV energies has long been debated. Here we report observations of very-high-energy $\gamma$-ray emission up to hundreds of TeV from two middle age shell-type SNRs, G150.3$+$4.5 and $\gamma$-Cygni, with the Large High Altitude Air Shower Observatory (LHAASO). Two (or three) distinct morphological/spectral components with convex spectral shapes are observed in both sources, with the low-energy one being more extended than the high-energy one. %Although it is possible that these high-energy components may be driven by powerful pulsars, The likely association of the high-energy component with molecular clouds at similar distances, and the weakness/absence of pulsar wind nebulae (PWNe) inside these SNRs clearly indicate for the first time that the highest energy emission is produced by collision of hadronic CRs up to PeV energies with the clouds. These results are compatible with the classic model prediction that PeV particles accelerated near the end of the free expansion phase of SNR evolution can illuminate nearby molecular clouds (MCs) to produce strong $\gamma$-ray emission.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

4 major / 2 minor

Summary. The manuscript reports LHAASO observations of very-high-energy gamma-ray emission up to hundreds of TeV from two middle-aged shell-type SNRs (G150.3+4.5 and γ-Cygni). It identifies two (or three) distinct morphological/spectral components with convex shapes per source, with the low-energy component more extended than the high-energy one. The central claim is that the highest-energy emission arises from hadronic collisions of PeV cosmic rays with molecular clouds at similar distances, supported by morphological distinctions, likely MC associations, and weakness/absence of PWNe; this is presented as compatible with classic SNR models of late free-expansion phase acceleration illuminating nearby clouds.

Significance. If the hadronic PeV interpretation is substantiated, the result would provide important observational support for SNRs accelerating particles to the cosmic-ray knee, directly linking new LHAASO data to longstanding theoretical predictions about cloud illumination by late-stage accelerated CRs. The morphological component separation adds a useful diagnostic for distinguishing emission processes in middle-aged SNRs.

major comments (4)
  1. [Abstract] Abstract: the claim that the high-energy component is produced by hadronic CRs up to PeV energies with MCs rests on 'likely association with molecular clouds at similar distances' without any reported distance/velocity overlap measurements, gas-mass estimates, or diffusion-time parameters for these specific SNRs.
  2. [Abstract] Abstract: no calculation is shown demonstrating that the observed VHE flux matches the expected pion-decay luminosity for a CR spectrum extending to PeV energies, leaving the hadronic flux normalization unverified.
  3. [Abstract] Abstract: leptonic alternatives (IC from SNR electrons or bremsstrahlung) are excluded only qualitatively via extension differences and lack of pulsar signatures, without quantitative spectral modeling, fit parameters, or multi-wavelength limits to demonstrate exclusion.
  4. [Abstract] Abstract: convex spectra are noted but without reported fit parameters, statistical significances, background-subtraction details, or direct comparison of hadronic vs. leptonic model predictions, the spectral distinction remains insufficient to secure the interpretation.
minor comments (2)
  1. Clarify whether two or three components are identified for each source individually and provide the exact morphological/spectral criteria used for separation.
  2. Ensure all statements about 'weakness/absence of PWNe' include specific observational upper limits or references rather than qualitative description.

Simulated Author's Rebuttal

4 responses · 0 unresolved

We are grateful to the referee for the thorough review and valuable suggestions. We have prepared detailed responses to each major comment and will incorporate revisions to enhance the clarity and rigor of our claims, particularly in the abstract and supporting sections.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the claim that the high-energy component is produced by hadronic CRs up to PeV energies with MCs rests on 'likely association with molecular clouds at similar distances' without any reported distance/velocity overlap measurements, gas-mass estimates, or diffusion-time parameters for these specific SNRs.

    Authors: The abstract provides a concise summary, but the full manuscript elaborates on the associations with molecular clouds based on positional overlaps from CO surveys and distance estimates from the literature. To address the referee's concern, we will revise the abstract to briefly note the supporting multi-wavelength data and add explicit values for distance overlaps, gas mass estimates, and diffusion time calculations in a new subsection of the discussion. This will provide the quantitative basis for the 'likely association'. revision: yes

  2. Referee: [Abstract] Abstract: no calculation is shown demonstrating that the observed VHE flux matches the expected pion-decay luminosity for a CR spectrum extending to PeV energies, leaving the hadronic flux normalization unverified.

    Authors: We agree that a direct flux comparison strengthens the interpretation. Although the paper emphasizes the morphological and spectral evidence, we will include in the revised manuscript an estimate of the expected pion-decay gamma-ray luminosity. This will use the total energy in PeV CRs inferred from the SNR shock parameters, the target gas density from the associated clouds, and the interaction efficiency, showing that it is consistent with the observed VHE flux for a spectrum extending to PeV energies. revision: yes

  3. Referee: [Abstract] Abstract: leptonic alternatives (IC from SNR electrons or bremsstrahlung) are excluded only qualitatively via extension differences and lack of pulsar signatures, without quantitative spectral modeling, fit parameters, or multi-wavelength limits to demonstrate exclusion.

    Authors: The exclusion relies on the distinct morphologies and the lack of detected PWNe or pulsars in these middle-aged SNRs. To make this more quantitative, we will add to the revised paper spectral modeling comparisons, including the required magnetic field strengths and electron spectra for leptonic models to reproduce the high-energy component, and compare with X-ray upper limits from archival data. Fit parameters for the gamma-ray spectra will also be reported explicitly. revision: yes

  4. Referee: [Abstract] Abstract: convex spectra are noted but without reported fit parameters, statistical significances, background-subtraction details, or direct comparison of hadronic vs. leptonic model predictions, the spectral distinction remains insufficient to secure the interpretation.

    Authors: Details on the spectral analysis, including background subtraction methods, are provided in the methods section of the manuscript. We will update the abstract and main text to include the specific fit parameters (e.g., spectral indices before and after the break, break energy), the statistical significance of the convex shape (e.g., via likelihood ratio tests), and direct overlays of hadronic (pion-decay) and leptonic (IC) model predictions on the observed spectra to demonstrate the preference for the hadronic scenario. revision: yes

Circularity Check

0 steps flagged

No significant circularity; new observations interpreted against standard external models

full rationale

The paper presents fresh LHAASO gamma-ray data on two SNRs, identifies distinct morphological/spectral components, and interprets the compact high-energy emission as hadronic PeV CR collisions with MCs on the basis of extension differences, lack of PWN signatures, and 'likely association' at similar distances. This is stated as compatible with the pre-existing 'classic model' of late free-expansion acceleration rather than derived from any internal fit, self-defined quantity, or self-citation chain. No equations or steps reduce the central claim to a tautology or to parameters fitted within the paper itself; the load-bearing assumptions are qualitative and rest on external astrophysical priors and the new observations.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The interpretation relies on established astrophysical models of SNR shock acceleration and hadronic gamma-ray production; no new free parameters or invented entities are introduced.

axioms (1)
  • domain assumption Gamma rays from hadronic cosmic-ray interactions with molecular gas produce convex spectra distinguishable from leptonic processes by morphology and lack of PWNe
    Invoked to attribute the high-energy component to PeV hadronic CRs rather than alternative mechanisms.

pith-pipeline@v0.9.0 · 7104 in / 1275 out tokens · 43568 ms · 2026-05-08T10:19:12.192623+00:00 · methodology

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