EDP Sciences
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Volume 417, Number 1, April I 2004
Page(s) 71 - 78
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20035883

A&A 417, 71-78 (2004)
DOI: 10.1051/0004-6361:20035883

X-ray flares reveal mass and angular momentum of the Galactic Center black hole

B. Aschenbach1, N. Grosso2, D. Porquet1 and P. Predehl1

1  Max-Planck-Institut für extraterrestrische Physik, PO Box 1312, Garching bei München 85741, Germany
2  Laboratoire d'Astrophysique de Grenoble, Université Joseph-Fourier, BP53, 38041 Grenoble Cedex 9, France

(Received 16 December 2003 / Accepted 23 January 2004 )

We have analysed the light curve of the two brightest X-ray flares from the Galactic Center black hole, one flare observed by XMM-Newton on October 3, 2002 (Porquet et al. [CITE]), and the other flare observed by Chandra on October 26, 2000 (Baganoff et al. [CITE]). The power density spectra show five distinct peaks at periods of ~100 s, 219 s, 700 s, 1150 s, and 2250 s common to both observations within their estimated measurement uncertainties. The power density spectrum of the recently reported infrared flare of June 16, 2003 (Genzel et al. [CITE]) shows distinct peaks at two, if not three, periods (including the $1008 \pm 120$ s infrared period), which are consistent with the X-ray periods. The remaining two periods could not be covered by the infrared measurements. Each period can be identified with one of the characteristic gravitational cyclic modes associated with accretion disks, i.e. either Lense-Thirring precession, Kepler orbital motion and the vertical and radial epicyclic oscillation modes, in such a way that a consistent value for the black hole mass of  $M\sb{\rm {BH}} = 2.72\sp{+0.12}\sb{-0.19}\times 10\sp 6~M_\odot$ and the angular momentum $a = 0.9939\sp{+0.0026}\sb{-0.0074}$ is obtained. The available data on  $M\sb{\rm {BH}}$ derived from studies of the orbital motion of the S2 (S0-2) star (Schödel et al. [CITE]; Ghez et al. [CITE]) agree with our findings. Finally we discuss some implications of the fairly high value for the angular momentum.

Key words: Galaxy: center -- X-rays: individuals: Sgr A* -- radiation mechanisms: general -- relativity -- Galaxy: nucleus -- Galaxy: fundamental parameters

Offprint request: B. Aschenbach, bra@mpe.mpg.de

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