Locating the gamma-ray emission site in Fermi/LAT blazars. II Multifrequency correlations

TL;DR

This study analyzes multi-frequency light curves of 15 blazars to identify correlations between gamma-ray, optical, and millimetre emissions, revealing mostly simultaneous variability and highlighting the influence of large flares.

Contribution

It provides the first detailed cross-correlation analysis across multiple bands for a sample of blazars, emphasizing the role of long-term variations and large flares in emission correlations.

Findings

Strong correlation between 37 and 95 GHz with near-zero delay.

Optical and gamma-ray bands also show significant correlation.

Less than half of the sources show strong correlations, likely due to lack of major outbursts.

Abstract

In an attempt to constrain and understand the emission mechanism of gamma rays, we perform a cross-correlation analysis of 15 blazars using light curves in millimetre, optical and gamma rays. We use discrete correlation function and consider only correlations significant at 99 per cent level. A strong correlation was found between 37 and 95 GHz with a near-zero time delay in most of the sources, and ~1 month or longer in the rest. A similar result was obtained between the optical and gamma-ray bands. Of the 15 sources, less than 50 per cent showed a strong correlation between the millimetre and gamma-ray or millimetre and optical bands. The primary reason for the lack of statistically significant correlation is the absence of a major outburst in the millimetre bands of most of the sources during the 2.5 yr time period investigated in our study. This may indicate that only the long-term variations or large flares are correlated between these bands. The variability of the sources at every waveband was also inspected using fractional rms variability. The fractional rms variability displays an increase with frequency reaching its maximum in the gamma rays.