arXiv subjects

A. Hankla

Publications and source records attributed to A. Hankla.

2 recordsLinked to original sources

arXiv2025

An outflow from the X-ray corona as the origin of millimeter emission from radio-quiet AGN

Recent observations of radio-quiet active galactic nuclei (RQAGN) have shown the presence of millimeter emission, whose origin remains unknown, from within parsec scales of the central black hole. We argue that the mm emission comes from a spatially extended region that is magnetically connected to the compact X-ray corona, in analogy to the solar wind and corona. We present an analytic model scaled to corona values in which non-equipartition electrons from multiple heights along an extended conical outflow shape the mm emission. In this model, the 100 GHz emission originates from within $\lesssim10^4$ gravitational radii ($r_g$) of the central black hole, though the projected distance from the black hole can be as low as $50r_g$ depending on the line-of-sight. Our model predicts a flat emission spectrum $F_{\nu}\sim{\rm const}$ and a mm-to-X-ray luminosity ratio $L_{\rm mm}/L_X\sim10^{-4}$, consistent with observations. These quantities depend weakly on the underlying electron power-law distribution function and black hole mass. We demonstrate this model's plausibility using a general relativistic magneto-hydrodynamic (GRMHD) simulation of a thin accretion disc as a case study. Our model highlights the need to study continual dissipation along the outflow to connect the X-ray- and mm-emitting regions.

astro-ph.HE↗

arXiv2025

The inner structure and thermodynamics of a thin accretion disc

Using three-dimensional general relativistic magnetohydrodynamic simulations with electron and proton thermodynamics and an electron cooling function, we probe the inner radial and vertical structure of weakly magnetized geometrically thin accretion discs around rapidly spinning black holes. We find that the thin, cold disc transitions to a thick, hot accretion flow at a radius dependent on the mass accretion rate due to proton-electron Coulomb decoupling. At high accretion rates, the disc truncates close to the innermost stable circular orbit $r\approx2r_g$, demonstrating that even in the canonical thin disc model, the plunging region should be treated with two-temperature physics. At intermediate accretion rates, the transition radius moves outward by a factor of two to $r\approx 5r_g$, forming a radiatively inefficient inner flow. The simulations also reveal extended cooling along the surface of the disc out to $\sim10r_g$, with 40\% of the total cooling at intermediate accretion rates occurring above the disc body. Two-temperature effects also impact the emission from within the plunging region of the black hole, leading to less thermal emission than predicted by single-temperature models. These results have implications for X-ray binary state transitions, the physical origin of the X-ray corona, and spin measurements that rely on determining the location of the innermost stable circular orbit.

astro-ph.HE↗