# The Ratio of the Core to the Extended Emissions in the Comoving Frame for Blazars

## TL;DR

This study investigates the ratio of core to extended emissions in blazars, revealing differences between BL Lacs and FSRQs and correlations with other jet parameters, using a sample of 65 blazars.

## Contribution

It introduces a method to estimate the core to extended emission ratio in blazars and analyzes its relation to various jet properties, highlighting differences between blazar subclasses.

## Key findings

- BL Lacs have a larger average core to extended emission ratio than FSRQs.
- The ratio $f$ correlates with intrinsic peak frequency, polarization, and core dominance.
- The ratio $f$ can be estimated using the core-dominance parameter $R$.

## Abstract

In a two-component jet model, the emissions are the sum of the core and extended emissions: $S^{\rm ob}=S_{\rm core}^{\rm ob}+S_{\rm ext}^{\rm ob}$, with the core emissions, $S_{\rm core}^{\rm ob}= f S_{\rm ext}^{\rm ob}\delta^{q}$, being a function of the Doppler factor, $\delta$, the extended emission, $S_{\rm ext}^{\rm ob}$, jet type dependent factor, $q$, and the ratio of the core to the extended emissions in the comoving frame, $f$. The $f$ is an unobservable but important parameter. Following our previous work, we collect 65 blazars with available Doppler factor, $\delta$, superluminal velocity, $\beta_{app}$, and core-dominance parameter, $R$, calculate the ratio, $f$, and peform statistical analyses. We find that the ratio, $f$, in BL Lacs is on average larger than that in FSRQs. We suggest that the difference of the ratio $f$ between FSRQs and BL Lacs is one of the possible reasons that cause the difference of other observed properties between them. We also find some significant correlations between $\log f$ and other parameters, including intrinsic (de-beamed) peak frequency, $\log \nu _{\rm p}^{\rm in}$, intrinsic polarization, $\log P^{\rm in}$, and core-dominance parameter, $\log R$, for the whole sample. In addition, we show that the ratio, $f$, can be estimated by $R$.