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Issue A&A
Volume 374, Number 3, August II 2001
Page(s) L19 - L20
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20010791



A&A 374, L19-L20 (2001)
DOI: 10.1051/0004-6361:20010791

A precise determination of black hole spin in GRO J1655-40

M. A. Abramowicz1, 2, 3 and W. Kluzniak4, 2

1  Department of Astronomy and Astrophysics, Chalmers University, 412-96 Göteborg, Sweden
2  Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
3  Université Pierre & Marie Curie (Paris VI), France
4  Institute of Astronomy Johannes Kepler, University of Zielona Góra, ul. Lubuska 2, 65-265 Zielona Góra, Poland

(Received 21 May 2001 / Accepted 5 June 2001 )

Abstract
We note that the recently discovered 450 Hz frequency in the X-ray flux of the black hole candidate GRO J1655-40 is in a 3:2 ratio to the previously known 300 Hz frequency of quasi-periodic oscillations (QPO) in the same source. If the origin of high frequency QPOs in black hole systems is a resonance between orbital and epicyclic motion of accreting matter, as suggested previously, the angular momentum of the black hole can be accurately determined, given its mass. We find that the dimensionless angular momentum is in the range 0.2< j< 0.67 if the mass is in the (corresponding) range of 5.5 to 7.9 solar masses.


Key words: equation of state -- relativity -- stars: black holes -- X-rays

Offprint request: W. Kluzniak, wlodek@camk.edu.pl

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