The Energy Budget in the Jet of High-frequency Peaked BL Lacertae Objects

TL;DR

This study analyzes the energy distribution and equipartition in the jets of high-frequency peaked BL Lac objects (HBLs), revealing that electrons dominate the energy budget and jets are likely powered by advection-dominated flows.

Contribution

It provides the first comprehensive statistical analysis of the energy budget and equipartition in a large sample of HBLs using spectral energy distribution modeling.

Findings

SEDs are well fitted by the one-zone lepton model.

Electrons carry significantly more energy than magnetic fields.

HBL jets likely have low radiation efficiency and are powered by advection-dominated flows.

Abstract

Energy equipartition and the energy budget in the jet are import issues for the radiation mechanism of blazars. Early work predominantly concentrated on flat-spectrum radio quasars and a limited number of BL Lacertae objects (BL Lacs). In this paper, we compile 348 high-frequency peaked BL Lac objects (HBLs) based on the catalog of active galactic nuclei (4LAC-DR3) from Fermi-LAT, and employ \textit{JetSet} to fit the spectral energy distributions (SEDs) of these HBLs in the framework of the one-zone lepton model. We aim to determine whether the energy budget is reasonable and whether the energy equipartition is satisfied in HBLs. The results of the statistical analysis suggest that: (1) SEDs of HBLs can be reproduced well by using the one-zone lepton model; however it cannot achieve the energy equalization, and the relativistic electron energy density is far greater than the magnetic field energy density, $U_{e} \gtrsim100 U_{B}$; (2) the majority of the HBLs are located in the $t_{cool}$$<$$t_{dyn}$ region (where the horizontal coordinate represents the jet power of electrons, while the ordinate indicates the ratio between the dynamic time scale to the cooling timescale), and the jet kinetic power of HBLs is greater than the jet power of radiation; there is a very low radiation efficiency, we deduce that HBLs may have optically thin advection-dominated accretion flows; (3) the $\log\epsilon_{B}$ of HBLs is less than zero, which indicates that the jet kinetic power of HBLs is not affected by Poynting flux; (4) the relationships with $U_{e} >U_{Syn}\sim U_{B}$, $L_{e}\sim L_{p}>L_{B}\sim L_{rad}$ and $\log\epsilon_{e}>0.5$ are established. These relations indicate that most of the energy of HBLs is stored in the population of low-energy electrons.