Discovery of a kilohertz quasi-periodic oscillation in 2S 0918‒549

We report the discovery of a kilohertz quasi-periodic oscillation (kHz QPO) in the low-mass X-ray binary (LMXB) 2S 0918-549. The kHz QPO has a frequency of 1156 ± 9 Hz, an FWHM of 70 ± 20 Hz, and a fractional rms amplitude of 18% ± 2%. We also detected for the first time a type I X-ray burst in this...

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Detalles Bibliográficos
Autores principales: Jonker, Peter G., Klis, Michiel van der, Homan, Jeroen, Méndez, Mariano R., Paradijs, Jan van, Belloni, Tomaso, Koueliotou, Chryssa, Lewin, Walter, Ford, Eric C.
Formato: Articulo
Lenguaje:Inglés
Publicado: 2001
Materias:
Ciencias Astronómicas
Accretion, accretion disks
Binaries: Close
Stars: Individual (2S 0918-549)
Stars: Neutron
Stars: Oscillations
X-rays: Stars
Acceso en línea:http://sedici.unlp.edu.ar/handle/10915/84707
Aporte de:
SEDICI (UNLP) de Universidad Nacional de La Plata
Descripción
Sumario:We report the discovery of a kilohertz quasi-periodic oscillation (kHz QPO) in the low-mass X-ray binary (LMXB) 2S 0918-549. The kHz QPO has a frequency of 1156 ± 9 Hz, an FWHM of 70 ± 20 Hz, and a fractional rms amplitude of 18% ± 2%. We also detected for the first time a type I X-ray burst in this source. The compact object must therefore be a neutron star. Finally, we were able to classify the source as an atoll source exhibiting the full complement of spectral/timing states of this class (island and banana). From the peak burst flux, an upper limit on the persistent luminosity can be derived of 0.5% of the Eddington luminosity, making 2S 0918-549 one of the least luminous LMXBs showing a kHz QPO. We compare the fractional rms amplitudes of the upper kHz QPO across the ensemble of LMXBs. We find a strong anticorrelation with luminosity. In LMXBs with luminosities ∼ 100 times lower than those of Z sources, the fractional rms amplitude is a factor ∼ 10 larger.

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