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A recent study applied a particle‑acceleration model for winds driven by massive star clusters to explain the high‑energy γ‑ray light from the Cygnus bubble. By jointly fitting the spectral energy distribution and the surface‑brightness profile, researchers found that Bohm‑type diffusion gave the lowest reduced χ² = 6.16, compared with 31.88 for Kolmogorov and 10.09 for Kraichnan. The analysis also highlights that uncertainties in the distances and three‑dimensional positions of molecular clouds inside the bubble limit the precision of derived gas densities and, consequently, the predicted γ‑ray and neutrino fluxes.
| MCMC-fit model parameters for the Cygnus bubble | ||||||
| Parameter | Best fit | Fit range | Prior/Range | |||
| Kolmogorov |
| Kraichnan |
| Bohm |
| Bohm |
| Fitted | Wind velocity usw [km s-1] | 2999.31 | 2999.96 | 2961.55 | 2896.14−357.29+98.94 | 1000–3000 |
| Mass-loss rate M˙⋆ [M⊙ yr-1] | 9.99×10−4 | 1×10−3 | 9.49×10−5 | (1.23−0.49+0.75)×10−4 | 10−6–10−3 |
| Ambient density ϱ0 [mp cm-3] | 1.02 | 1.08 | 6.58 | 7.67−3.56+2.24 | 1–10 |
| System age 𝒯age [Myr] | 5.83 | 2.40 | 6.80 | 6.69−0.96+0.29 | 2–7 |
| Magnetic-energy fraction ηB | 0.1 | 0.1 | 0.078 | 0.068−0.032+0.030 | 0.001–0.1 |
| Spectral index s | 4.17 | 4.29 | 4.34 | 4.34−0.017+0.012 | 4–5 |
| CR-energy fraction ϵcr | 0.021 | 0.010 | 0.020 | 0.016−0.005+0.012 | 0.001–0.1 |
| Cygnus North Filament [pc] | 171.37 | 168.96 | 161.07 | 160.49−86.64+20.31 | 10–260 |
| Cygnus Central Clumps [pc] | 176.06 | 179.25 | 30.18 | 32.43−3.34+138.51 | 10–260 |
| Cygnus West [pc] | 88.33 | 166.64 | 159.44 | 159.13−88.49+21.72 | 10–260 |
| Cygnus SFR South [pc] | 86.91 | 60.04 | 163.43 | 162.84−9.35+10.68 | 10–260 |
| Cygnus South Filament [pc] | 171.28 | 166.43 | 169.14 | 162.96−9.91+14.11 | 10–260 |
| Cygnus Far South [pc] | 88.02 | 159.01 | 87.35 | 158.13−89.95+25.18 | 10–260 |
| Derived | Total wind luminosity ℒsw [erg s-1] | 2.83×1039 | 2.83×1039 | 2.62×1038 | — | — |
| Shock radius ℛsh [pc] | 86.84 | 59.85 | 26.03 | — | — |
| Bubble radius ℛb [pc] | 394.18 | 228.73 | 185.14 | — | — |
| Post-shock δℬsw [μG] | 12.01 | 17.45 | 10.85 | — | — |
| Maximum energy Emax [PeV] | 14.83 | 7.63 | 3.28 | — | — |
| Combined reduced chi-square χred2 | 31.88 | 10.09 | 6.16 | — | — |
| IceCube | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Diffusion Model | 1 yr | 5 yr | 10 yr | ||||||
| 𝒩event | 𝒩bkg | σ | 𝒩event | 𝒩bkg | σ | 𝒩event | 𝒩bkg | σ | |
| Bohm | 9.47 | 53.03 | 1.30 | 47.33 | 265.16 | 2.91 | 94.67 | 530.33 | 4.11 |
| Kraichnan | 10.27 | 53.03 | 1.41 | 51.33 | 265.16 | 3.15 | 102.65 | 368.69 | 4.46 |
| Kolmogorov | 10.03 | 53.03 | 1.38 | 50.14 | 265.16 | 3.08 | 100.27 | 368.69 | 4.35 |
| KM3NeT/ARCA | |||||||||
| Bohm | 5.85 | 33.77 | 1.01 | 29.24 | 168.84 | 2.25 | 58.47 | 337.68 | 3.18 |
| Kraichnan | 6.33 | 33.77 | 1.09 | 31.65 | 168.84 | 2.44 | 63.30 | 337.68 | 3.44 |
| Kolmogorov | 6.17 | 33.77 | 1.06 | 30.87 | 168.84 | 2.38 | 61.74 | 337.68 | 3.36 |