Temporal 1/f^α fluctuations from fractal magnetic fields in black-hole accretion flow

Rapid fluctuation with a frequency dependence of 1/f^α (with α ≃ 1-2) is characteristic of radiation from black-hole objects. Its origin remains poorly understood. We examined three-dimensional magnetohydrodynamical simulation data, finding that a magnetized accretion disk exhibits both 1/f^α fluctuation (with α ≃ 2) and a fractal magnetic structure (with the fractal dimension of D ∼ 1.9). The fractal field configuration leads to reconnection events with a variety of released energy and duration, thereby producing 1/f^α fluctuations.