The Super PeVatron: LHAASO Unlocking the High-Energy Secrets of Cygnus X-3

In this episode, we dive into a groundbreaking discovery from the **Large High Altitude Air Shower Observatory (LHAASO)**. For decades, the microquasar **Cygnus X-3** has been "an astronomical puzzle," but new data has finally confirmed its status as a **Super PeVatron**—a cosmic engine capable of accelerating protons to tens of petaelectronvolt (PeV) energies.

**Key Discussion Points:**

• **The Iconic Microquasar:** Cygnus X-3 is a unique high-mass X-ray binary consisting of a compact object (a black hole or neutron star) and a massive **Wolf–Rayet donor star**. It features a relativistic jet and a remarkably short 4.8-hour orbital period.
• **Breaking the Energy Barrier:** LHAASO detected variable gamma-rays reaching up to **3.7 PeV**, the highest-energy photons ever recorded from such an astrophysical source.
• **The Hardest Spectrum:** The source exhibits the **hardest ultra-high-energy (UHE) spectrum** ever detected by LHAASO, with a distinct "hump" or spectral hardening around 1 PeV.
• **Protons vs. Electrons:** While lower-energy GeV gamma-rays are often produced by electrons, researchers explain that **leptonic origins are robustly excluded** for these PeV emissions due to intense synchrotron cooling. Instead, the signal likely comes from **photomeson processes**, where protons accelerated in the jet collide with the dense ultraviolet and X-ray photon fields of the binary system.
• **Temporal Puzzles:** We discuss the **month-scale variability** of the signal and the 3.2$\sigma$ evidence for orbital modulation, which strongly suggests the PeV radiation is born deep within the innermost regions of the jet.

The Big Picture:

This discovery provides the first compelling evidence that a microquasar can act as a **super-PeVatron**, generating transient PeV gamma-ray emission in close proximity to the central engine. This shifts our understanding of how cosmic rays are accelerated within our own galaxy.

### Article Reference

**Title:** *Cygnus X-3: A variable petaelectronvolt gamma-ray source*

**Authors:** The LHAASO Collaboration

**Journal:** *National Science Review (NSR)*

**Source PDF:** 2512.16638v1.pdf

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: LHAASO Collaboration