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Astron. Astrophys. 358, 617-623 (2000)

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Fourier power spectra at high frequencies: a way to distinguish a neutron star from a black hole

R. Sunyaev 1,2 and M. Revnivtsev 2,1

1 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85740 Garching bei München, Germany
2 Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117810 Moscow, Russia

Received 17 April 2000 / Accepted 19 April 2000


We analyzed the power density spectra of a sample of 9 neutron star and 9 black hole binaries in the low/hard spectral state. In the power density spectra of accreting neutron stars with a weak magnetic field a significant power is contained at frequencies close to one kHz. At the same time, most Galactic accreting black holes demonstrate a strong decline in the power spectra at the frequencies higher than 10-50 Hz. We propose to use this empirical fact as a method to distinguish the accreting neutron stars from black holes in X-ray transients. The X-ray transients that demonstrate significant noise in their X-ray flux at frequencies above [FORMULA] Hz should be considered neutron stars. We propose to explain the observed difference as a result of the existence of a radiation dominated spreading layer on the neutron star surface (Inogamov & Sunyaev 1999). The possible very high frequency variabilities of this layer are discussed.

Key words: accretion, accretion disks – instabilities – stars: binaries: general – stars: fundamental parameters – stars: neutron – X-rays: general

Send offprint requests to: revnivtsev@hea.iki.rssi.ru

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© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000