The observed radio/gamma-ray emission correlation for blazars with the Fermi-LAT and the RATAN-600 data

TL;DR

This study investigates the correlation between radio and gamma-ray emissions in blazars, revealing that the correlation varies with energy and frequency, and is generally stronger at lower gamma-ray energies, with implications for understanding blazar emission mechanisms.

Contribution

It provides a comprehensive analysis of radio/gamma-ray correlations in blazars using simultaneous data, highlighting differences between BL Lac objects and FSRQs across energy bands.

Findings

Positive correlation at low gamma-ray energies for BL Lacs and FSRQs.

Correlation weakens or becomes negative at higher gamma-ray energies.

Statistically significant correlations below 3 GeV, especially for BL Lacs.

Abstract

We study the correlation between gamma-ray and radio band radiation for 123 blazars, using the Fermi-LAT first source catalog (1FGL) and the RATAN-600 data obtained at the same period of time (within a few months). We found an apparent positive correlation for BL Lac and flat-spectrum radio quasar (FSRQ) sources from our sample through testing the value of the Pearson product-moment correlation coefficient. The BL Lac objects show higher values of the correlation coefficient than FSRQs at all frequencies, except 21.7 GHz, and at all bands, except $10-100$ GeV, typically at high confidence level (> 99%). At higher gamma-ray energies the correlation weakens and even becomes negative for BL Lacs and FSRQs. For BL Lac blazars, the correlation of the fluxes appeared to be more sensitive to the considered gamma-ray energy band, than to the frequency, while for FSRQ sources the correlation changed notably both with the considered radio frequency and gamma-ray energy band. We used a data randomization method to quantify the significance of the computed correlation coefficients. We find that the statistical significance of the correlations we obtained between the flux densities at all frequencies and the photon flux in all gamma-ray bands below 3 GeV is high for BL Lacs (chance probability $\sim 10^{-3} - 10^{-7}$). The correlation coefficient is high and significant for the $0.1-0.3$ GeV band and low and insignificant for the $10-100$ GeV band for both types of blazars for all considered frequencies.