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Published on: July 1, 2019
Transient Large-Scale Anisotropy in TeV Cosmic Rays due to an Interplanetary Coronal Mass Ejection.
Zhen Cao1,2,3, F Aharonian3,4,5,6, Y X Bai1,3
1State Key Laboratory of Particle Astrophysics and Experimental Physics Division and Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, 100049 Beijing, China.
Physical Review Letters
|July 10, 2026
Summary
Scientists observed the first-ever transient large-scale cosmic ray anisotropy at TeV energies. This discovery using the Large High-Altitude Air Shower Observatory offers new insights into space weather and magnetic fields.
Area of Science:
- Cosmic ray physics
- Astrophysics
- Space physics
Background:
- Previously, time-varying cosmic ray anisotropy was only observed at energies below 150 GeV.
- Such transient changes are often linked to interplanetary shocks and solar storm events.
- Large-scale cosmic ray anisotropy at TeV energies has not been previously confirmed to vary with time.
Purpose of the Study:
- To report the first observation of transient large-scale anisotropy in TeV cosmic ray ions.
- To analyze the characteristics of this transient anisotropy, including its energy dependence.
- To explore the potential of using air shower arrays for studying interplanetary magnetic structures.
Main Methods:
- Utilized data from the Large High-Altitude Air Shower Observatory (LHAASO).
- Analyzed hourly skymaps to identify transient cosmic ray intensity excesses or deficits.
- Determined the direction and magnitude of anisotropy from the intensity gradient.
Main Results:
- Observed enhanced anisotropy with >5σ significance on November 4, 2021, across multiple TeV energy ranges (0.6-2.8 TeV).
- Found the anisotropy gradient varies with energy as E^{γ}, with γ=-0.5.
- At median energies ≤1.0 TeV, this corresponds to a dipole anisotropy of at least 0.9%.
Conclusions:
- This marks the first detection of transient large-scale anisotropy in TeV cosmic rays.
- The observed energy-dependent gradient provides new information about the underlying physical processes.
- This finding opens new avenues for studying interplanetary magnetic structures using global air shower networks.
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