ar X iv : a st ro - p h / 01 08 16 4 v 1 9 A ug 2 00 1 Dependence of kHz QPO Properties on Normal - Branch Oscillation Phase in Scorpius X - 1

ar X iv : a st ro - p h / 01 08 16 4 v 2 1 3 A ug 2 00 1 Dependence of kHz QPO Properties on Normal - Branch Oscillation Phase in Scorpius X - 1

We analysed RXTE data of Sco X-1 which show kHz quasi-periodic oscillations (QPOs) and the ∼6–8 Hz normal-branch oscillation (NBO) simultaneously. Using power spectra of 0.03–0.5 s data segments, we find that both the upper kHz QPO frequency ν2 and the ratio of lower to upper kHz QPO amplitude are anticorrelated to variations in the X-ray count-rate taking place on the NBO time scale. The frequ...

ar X iv : a st ro - p h / 99 08 17 2 v 1 1 6 A ug 1 99 9 Phase Lags of QPOs in Microquasar GRS 1915 + 105

I report the discovery of hard X-ray phase lags associated with the famous 67 Hz quasi-periodic oscillation (QPO) in microquasar GRS 1915+105. The QPO is seen on multiple occasions. For this investigation, I have chosen one particular observation when the oscillation is the strongest. The measured hard lags show strong energy dependence. With respect to the 2-2.5 keV band, the phase lag increas...

ar X iv : a st ro - p h / 02 08 13 0 v 1 6 A ug 2 00 2 GX 339 – 4 : back to life

We report preliminary results of a RossiXTE campaign on the 2002 outburst of the black-hole candidate GX 339–4. We show power density spectra of five observations during the early phase of the outburst. The first four power spectra show a smooth transition between a Low State and a Very High State. The fifth power spectrum resembles a High State, but a strong 6 Hz QPO appears suddenly within 16...

ar X iv : a st ro - p h / 04 08 13 5 v 1 9 A ug 2 00 4 A Determination of the Chemical Composition of α Centauri A from Strong Lines

ar X iv : a st ro - p h / 01 08 45 0 v 1 2 8 A ug 2 00 1 Do Type - I Bursts Excite Modes in the Neutron - Star Ocean ?

During a Type-I burst, the turbulent deflagation front may excite waves in the neutron star ocean with frequencies, ω ∼ 1 Hz. These waves are observed as highly coherent flux oscillations during the burst. The frequencies of these waves changes as the upper layers of the neutron star cool which accounts for the small variation in the observed QPO frequencies. In principle several modes could be...