What Powers The Relativistic Jets Of Active Galactic Nuclei? (Planetary Science)

Summary

  • Yongyun Chen and colleagues by using a large sample of blazars detected by the Fermi Large Area Telescope (LAT), studied the relationship between jet powers and spin of supermassive black hole.
  • They found that the spin of supermassive black holes and accretion are the most important contribution to the jet kinetic power.
  • The contribution rates of both the spin of supermassive black holes and accretion are more than 95%.
  • These results suggest that the spin energy of supermassive black holes powers the relativistic jets.

Blazars are a special subclass of active galactic nuclei (AGN) whose jets point to the observer. Blazars are usually classified as flat-spectrum radio quasars (FSRQs) and BL Lac objects (BL Lacs) based on the equivalent width (EW) of the optical emission lines. The EW of FSRQs is large than 5A, while BL Lacs have EW ˚ <5A. Later, Ghisellini used the ratio of broad emission line to Eddington luminosity to divide the FSRQs and BL Lacs, namely accretion rate. They pointed out that FSRQs have L_BLR/L_Edd ≥ 5 × 10¯4, while BL Lacs are less than this value. This division between FSRQs and BL Lacs may imply that they have different accretion regime.

It is generally believed that the non thermal radiation of the blazars is originated from the relativistic jet. However, the formation of jets has always been an unsolved problem in astrophysics. Theoretical models showed that the power of relativistic jets of active galactic nuclei depends on the spin and mass of the central supermassive black holes, as well as the accretion. Now Y. Chen and colleagues, by using a large sample of blazars detected by the Fermi Large Area Telescope (LAT), studied the relationship between jet powers and spin of supermassive black hole.

They found significant correlation between jet kinetic power and the spin of supermassive black holes, which is consistent with theoretical models and numerical simulations. They also found significant correlation between jet kinetic power and accretion disk luminosity, which suggested a tight connection between jet and accretion. At the same time, the jet kinetic power is greater than the accretion disk luminosity, which indicated that the accretion is not enough to explain the jet kinetic power for Fermi blazars.

Figure 1. Radiative jet power (left panel) and jet kinetic power (right panel) vs the spin of supermassive black holes for FSRQs and BL Lacs, respectively. The radiative jet power and jet kinetic power estimated through a simple one–zone leptonic model. The large filled circles are FSRQs, while filled squares are BL Lacs. Shaded red colored areas correspond 3σ confidence bands. The two blue lines are the best least square fit logP_rad = 1.38logj + 45.83 and logPjet = 0.97logj + 46.83. The uper left corner shows the average error bar. The average uncertainty of Prad is a factor of 1.7; the average uncertainty of Pjet is a factor of 3. © Chen et al.

So, by using multiple linear regression they analyzed the relationship between jet kinetic power and accretion, spin and black hole mass. They found that the spin of supermassive black holes and accretion are the most important contribution to the jet kinetic power. The contribution rates of both the spin of supermassive black holes and accretion are more than 95%. These results suggest that the spin energy of supermassive black holes powers the relativistic jets.

“Our spin estimates are consistent with the results from models for the cosmological merger-driven evolution of supermassive black holes.”

— told Yongyun Chen, lead author of the study.

Finally, they concluded that the jet production efficiency of almost all Fermi blazars can be explained by moderately thin magnetically arrested accretion disks around rapidly spinning black holes.


Reference: Yongyun Chen, Qiusheng Gu, Junhui Fan, Hongyan Zhou, Yefei Yuan, Weimin Gu, Qinwen Wu, Dingrong Xiong, Xiaotong Guo, Nan Ding, Xiaoling Yu, “The Powers of Relativistic Jets depend on the Spin of Accreting Supermassive Black Hole”, ArXiv, pp. 1-15, 2021. https://arxiv.org/abs/2104.04242


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