A power-law break in the near-infrared power spectrum, of the Galactic center black hole

L. Meyer (1), T. Do (1), A. Ghez (1), M. R. Morris (1), S. Yelda (1) R. Schödel (2) A. Eckart (3)

(1) Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547
(2) Instituto de Astrofísica de Andalucía - CSIC, Camino Bajo de Huétor 50, 18008 Granada, Spain
(3) Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany

Paper: ApJ Letters, accepted


Proposed scaling relations of a characteristic timescale in the X-ray power spectral density of galactic and supermassive black holes have been used to argue that the accretion process is the same for small and large black holes. Here, we report on the discovery of this timescale in the near-infrared radiation of Sgr A*, the 4* 106 M\sun black hole at the center of our Galaxy, which is the most extreme sub-Eddington source accessible to observations. Previous simultaneous monitoring campaigns established a correspondence between the X-ray and near-infrared regime and thus the variability timescales are likely identical for the two wavelengths. We combined Keck and VLT data sets to achieve the necessary dense temporal coverage, and a time baseline of four years allows for a broad temporal frequency range. Comparison with Monte Carlo simulations is used to account for the irregular sampling. We find a timescale at 154+124_-87 min (errors mark the 90% c onfidence limits) which is inconsistent with a recently proposed scaling relation that uses bolometric luminosity and black hole mass as parameters. However, our result fits the expected value if only linear scaling with black hole mass is assumed. We suggest that the luminosity-mass-timescale relation applies only to black hole systems in the soft state. In the hard state, which is characterized by lower luminosities and accretion rates, there is just linear mass scaling, linking Sgr A* to hard state stellar mass black holes.

Preprints available from the authors at leo-meyer@gmx.de , or the raw TeX (no figures) if you click here.

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