Blazar spectral variability as explained by a twisted inhomogeneous jet

Area of Science:

• Astrophysics and cosmology
• High-energy astrophysics

Background:

• Blazars are active galactic nuclei emitting powerful radiation due to relativistic jets pointed towards Earth.
• Blazar variability is rapid and pronounced due to Doppler beaming, but its underlying mechanisms remain debated.
• Proposed mechanisms include particle acceleration/cooling, shocks, turbulence, or geometric effects like changing viewing angles.

Purpose of the Study:

• To investigate the cause of blazar variability, specifically the long-term flux and spectral changes observed in CTA 102.
• To test competing models for blazar emission, focusing on physical conditions versus geometric interpretations.

Main Methods:

• Optical-to-radio wavelength monitoring of the blazar CTA 102 over an extended period.
• Analysis of long-term trends in flux and spectral variability.
• Comparison of observational data with theoretical predictions, particularly those related to relativistic beaming and jet geometry.

Main Results:

• Observed long-term variability in CTA 102 is best explained by an inhomogeneous, curved jet whose orientation changes over time.
• An extreme optical outburst in 2016-2017 coincided with the emitting region having a small viewing angle.
• Changes in jet orientation alter Doppler factors, influencing observed flux and variability timescales.

Conclusions:

• The study supports a geometric interpretation of blazar variability, driven by jet orientation changes.
• Magnetohydrodynamic instabilities or jet rotation are proposed as causes for these orientation shifts.
• The findings provide further validation for the theory of relativistic beaming in blazar emission.