| Canonical Name: | Cygnus X-3 |
| TeVCat Name: | TeV J2032+409 |
| Other Names: | |
| Source Type: | BIN |
| R.A.: | 20 32 24 (hh mm ss) |
| Dec.: | +40 55 12 (dd mm ss) |
| Gal Long: | 79.81 (deg) |
| Gal Lat: | 0.68 (deg) |
| Distance: | 9.67 kpc |
| Flux: | (Crab Units) |
| Energy Threshold: | 50000 GeV |
| Spectral Index: | 2.18 |
| Extended: | No |
| Discovery Date: | 2025-12 |
| Discovered By: | LHAASO |
| TeVCat SubCat: | Newly Announced |
Source Notes:
Detection:
This detection was announced by
The LHAASO Collaboration (2026) in the National Science Review:
- "We report the discovery of variable gamma-rays up to
petaelectronvolt (PeV; 1 PeV = 10e15 eV) from Cygnus X-3, an iconic
X-ray binary. The gamma-ray signal was detected with a statistical
significance of approximately 10 sigma by the Large High Altitude Air
Shower Observatory (LHAASO)."
Source Position:
From
The LHAASO Collaboration (2026):
- R.A. (J2000): 20h 32m 24s +/- 0.12m stat +/- 0.12m syst (308.10deg +/- 0.03deg stat +/- 0.03deg syst)
- Dec. (J2000): +40d 55m 12s +/- 0.02deg stat +/- 0.03deg syst (40.92deg +/- 0.02deg stat +/- 0.03deg syst)
Distance:
From
Reid & Miller Jones (2023):
- "We report a highly accurate trigonometric parallax measurement for
Cyg X-3 using the Very Long Baseline Array at 43 GHz, placing the
source at a distance of (9.67 +0.53 -0.48) kpc."
Angular Extent:
From
The LHAASO Collaboration (2026):
- "Adopting a distance of 9 kpc
(Reid & Miller Jones, 2023), the
observed upper limit for angular extension constrains the physical
size of the gamma-ray emitter to be no more than 44 light-years."
Variability:
From
The LHAASO Collaboration (2026):
- "The detected month-scale variability, together with a 3.2 sigma
evidence for orbital modulation, suggests that the PeV gamma-rays
originate within, or in close proximity to, the binary system itself."
Flux and Spectral Information:
From
The LHAASO Collaboration (2026):
- "Its intrinsic spectral energy distribution (SED), extending from
0.06 to 3.7 PeV, shows a pronounced rise toward 1 PeV after accounting
for photon-photon absorption by the cosmic microwave background
radiation."
- "The spectrum of Cygnus X-3 is peculiar and differs from those of
all previously reported TeV/PeV sources. A strongly significant signal
is detected above 0.1 PeV, with detection significance of 7.1 sigma,
4.6 sigma, and 6.4 sigma in the 0.1 - 0.4 PeV, 0.4 - 1 PeV, and >1 PeV
intervals, respectively. The signal below 0.1 PeV reaches only 3.5
sigma, primarily contributed by a narrow energy interval between 63
and 100 TeV. No significant excess is detected in the WCDA data at
energies below 20 TeV."
- The flux is best fit with a power-law spectrum dN/dE = N0(E/E0)^-A
with the following parameters:
... E0: 50 TeV
... N0: (2.6 +/- 0.6) x10e-17 TeV-1 cm-1 s-1
... A: 2.18 +/- 0.14
"... characterizing Cygnus X-3 as the hardest UHE source ever detected
by LHAASO. There is a possible spectral hardening above 1 PeV, and
this trend becomes more pronounced when accounting for the absorption
of UHE gamma rays during their propagation from the source to the
observer."
Gamma-ray emission:
From
The LHAASO Collaboration (2026):
- Using the temporal variability and causality arguments the authors
state "At this spatial scale, the inner jet of Cygnus X-3 is by far
the most plausible site for particle acceleration and efficient
gamma-ray production, although alternative scenarios cannot be
entirely ruled out."
- "At GeV energies, the modulation of the gamma-ray signal with the
orbital period of Cygnus X- 3 has already been observed with high
statistical significance during the source’s high state by the
Fermi-LAT collaboration
Abdo et al. (2009). The correlation between
the GeV and PeV radiation components provides indirect but
compelling evidence that UHE gamma-rays are also produced at the binary
scale. Remarkably, the UHE gamma-ray data alone show evidence of
orbital modulation. The folded light curve
as a function of orbital phase exhibits a clear peak near phase 0.2
and a minimum around phase 0.6."
- The authors also state that "the correlation with the long-term
(monthly) variability observed in the GeV band enhances the confidence
of the result. Taken together, these observations strongly support the
conclusion that the PeV gamma-ray emission originates close to the
Cygnus X-3 binary system. As will be shown below, this is also
supported by the PeV spectral hardening."
Seen by: LHAASO
-
The counterjet dominates the production of PeV photons from Cyg X-3
Zdziarski, Andrzej A. et al., arXiv e-prints parXiv:2603.27805 (2026) [LINK]
-
Constraining the PeV gamma-ray emission zone of Cygnus X-3 with contemporaneous GeV timing and spectral observations
Zhang, Xing-Fu et al., arXiv e-prints parXiv:2604.04768 (2026) [LINK]
-
Long-term study of the gamma-ray emission of Cygnus X-3 with MAGIC and Fermi-LAT
Abe, K. et al., arXiv e-prints parXiv:2604.27671 (2026) [LINK]
-
From GeV to PeV: Orbital Modulation and Wind-Regulated Ultrahigh-energy Emission in Cygnus X-3
Wan, Su-Yu et al., arXiv e-prints parXiv:2610.11881 (2026) [LINK]
-
Cygnus X-3: A variable petaelectronvolt gamma-ray source
The LHAASO Collaboration et al., arXiv e-prints parXiv:2512.16638 (2025) [LINK]
-
Microquasars as the major contributors to Galactic cosmic rays around the ``knee''
Kaci, Samy et al., arXiv e-prints parXiv:2510.01369 (2025) [LINK]
-
On the Distances to the X-Ray Binaries Cygnus X-3 and GRS 1915+105
Reid, M.J. and Miller-Jones, J.C.~A., ApJ 959 p85 (2023) [LINK]
-
Modulated High-Energy Gamma-Ray Emission from the Microquasar Cygnus X-3
Fermi LAT Collaboration et al., Science 326 p1512 (2009) [LINK]
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