High Energy Astrophysical PhenomenaEnglishPublished
PeV‑scale gamma‑ray burst from Cygnus X‑3 probes limits on light‑speed violation
arXiv: 2611.14028v1
The Large High Altitude Air Shower Observatory (LHAASO) detected photons with energies up to 3.7 PeV coming from the binary system Cygnus X‑3. The event occurred during a flaring episode and the photons travel from a distance of about 9 kpc. Using a three‑dimensional spatial–spectral fitting framework, the team modeled Cygnus X‑3 as a point source and employed a baseline PγX+PγUV spectral shape. An additional hard spectral cut‑off parameter, E_cut, was introduced to test whether Lorentz invariance violation (LIV) could cause high‑energy photons to decay.
Analysis of the data, including corrections for absorption by the interstellar radiation field and the cosmic microwave background, gives a 95 % confidence–level lower limit of E_cut = 3.05 PeV. Using this limit, the study derives lower bounds on the LIV energy scale: for first‑order violations the scale is at least 2.72×10³⁴ eV, exceeding the Planck energy, and for second‑order violations the limits from photon decay and photon splitting are 9.09×10²⁴ eV and 1.73×10²⁶ eV, respectively.
Table shows the cutoff energy at 3.05 PeV and the resulting energy‑scale limits for first‑ and second‑order Lorentz‑invariance violation, including a 9.6 % systematic uncertainty.
Source
L
Erecmax
Ecut95%
ELIV(1)
ELIV(2)
ELIV(2) (3γ)
(kpc)
(PeV)
(PeV)
(eV)
(eV)
(eV)
×1032
×1023
×1025
Cygnus X-3
8.95
3.735±0.411
3.05−0.29+0.29
271.9−70.4+85.2
90.9−16.5+18.1
17.3−3.0+3.3
Table 1. Table 1 lists the 95 % CL lower limit on the hard‑cutoff energy E_cut = 3.05 PeV and the corresponding lower limits on the first‑ and second‑order Lorentz‑invariance‑violation energy scales derived for γ→e⁺e⁻ and γ→3γ processes, together with the quoted systematic uncertainty of ≈ 9.6 % on these limits.Cao, Zhen, Aharonian, F., Bai, Y. X., Bao, Y. W., Bastieri, D., Bi, X. J. et al. · arXiv:2611.14028v1 · Table 1: · CC BY 4.0
The choice of intrinsic spectrum affects the LIV bound only slightly; a simple power‑law model yields a comparable but slightly higher limit. The main systematic uncertainty comes from the spectral model of Cygnus X‑3, which contributes about 9.6 % uncertainty to the 95 % confidence limits on the LIV energy scales.
These results represent the most stringent constraints on LIV from gamma‑ray observations to date, demonstrating that photons at the PeV level can be produced and survive over galactic distances without showing the spectral cut‑off that would accompany superluminal Lorentz‑violating scenarios.