Rapid variability of BL Lac 0925+504: interstellar scintillation induced?

TL;DR

This study investigates rapid variability in BL Lac 0925+504 at 4.85 GHz, suggesting it is mainly caused by interstellar scintillation from a nearby scattering screen approximately 110 parsecs away.

Contribution

The paper provides a detailed analysis of the variability, demonstrating that interstellar scintillation near the observer explains the rapid changes and potential annual modulation.

Findings

Variability is caused by interstellar scintillation close to the observer.

The scattering screen is located approximately 110 parsecs away.

Evidence of annual modulation in variability timescales detected.

Abstract

Analysis of rapid variability at 4.85 GHz for the BL BLac object 0925+504 is presented and discussed. The structure functions (SF) are investigated with both refractive and weak interstellar scintillation (RISS/WISS) models analytically. Parameters obtained with these models are quantitatively compared, suggesting that the emission region of IDV is remarkably compact and the responsible interstellar scintillation medium (ISM) lies very close to the observer. Furthermore possible evidence of annual modulation of the variability timescales is detected in this source. Our findings indicate that the observed rapid variability in 0925+504 is predominantly caused by a scattering screen located along the line of sight to the source, at a distance of $\sim 110\,pc$ to the observer.