@article{13381,
  author = {G. Paraschos and J.-Y. Kim and M. Wielgus and Jason Dexter and et. al},
  title = {Ordered magnetic fields around the 3C 84 central black hole},
  abstract = {<p><i>Context.</i>&nbsp;3C 84 is a nearby radio source with a complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates the use of very-long-baseline interferometry (VLBI) above the hitherto available maximum frequency of 86 GHz.</p>

<p><i>Aims.</i>&nbsp;Using ultrahigh resolution VLBI observations at the currently highest available frequency of 228 GHz, we aim to perform a direct detection of compact structures and understand the physical conditions in the compact region of 3C 84.</p>

<p><i>Methods.</i>&nbsp;We used Event Horizon Telescope (EHT) 228 GHz observations and, given the limited (<i>u</i>, <i>v</i>)-coverage, applied geometric model fitting to the data. Furthermore, we employed quasi-simultaneously observed, ancillary multi-frequency VLBI data for the source in order to carry out a comprehensive analysis of the core structure.</p>

<p><i>Results.</i>&nbsp;We report the detection of a highly ordered, strong magnetic field around the central, supermassive black hole of 3C 84. The brightness temperature analysis suggests that the system is in equipartition. We also determined a turnover frequency of&nbsp;<i>ν</i><sub>m</sub> = (113 ± 4) GHz, a corresponding synchrotron self-absorbed magnetic field of&nbsp;<i>B</i><sub>SSA</sub> = (2.9 ± 1.6) G, and an equipartition magnetic field of&nbsp;<i>B</i><sub>eq</sub> = (5.2 ± 0.6) G. Three components are resolved with the highest fractional polarisation detected for this object (<i>m</i><sub>net</sub> = (17.0 ± 3.9)%). The positions of the components are compatible with those seen in low-frequency VLBI observations since 2017–2018. We report a steeply negative slope of the spectrum at 228 GHz. We used these findings to test existing models of jet formation, propagation, and Faraday rotation in 3C 84.</p>

<p><i>Conclusions.</i>&nbsp;The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C 84. However, systematic uncertainties due to the limited (<i>u</i>, <i>v</i>)-coverage, however, cannot be ignored. Our upcoming work using new EHT data, which offer full imaging capabilities, will shed more light on the compact region of 3C 84.</p>
},
  year = {2024},
  journal = {Astronomy & Astrophysics},
  volume = {682},
  pages = {L3},
  month = {2024-02},
  url = {https://doi.org/10.1051/0004-6361/202348308},
  doi = {10.1051/0004-6361/202348308},
}