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

• Autores: Jonker, Peter G.; Klis, Michiel van der; Homan, Jeroen; Méndez, Mariano R.; Paradijs, Jan van; Belloni, Tomaso; Koueliotou, Chryssa; Lewin, Walter; Ford, Eric C.
• Año de publicación: 2001
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Astronómicas; Accretion, accretion disks; Binaries: Close; Stars: Individual (2S 0918-549); Stars: Neutron; Stars: Oscillations; X-rays: Stars
• Institución: Universidad Nacional de La Plata

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.
Facultad de Ciencias Astronómicas y Geofísicas