@inproceedings{oai:jaxa.repo.nii.ac.jp:00005261,
 author = {Paul, Biswajit and Raichur, H.},
 book = {宇宙航空研究開発機構特別資料, JAXA Special Publication: Astrophysics with All-Sky X-Ray observations: 3rd International MAXI Workshop},
 month = {Feb},
 note = {Astrophysics with All-Sky X-Ray observations: 3rd International MAXI Workshop (RIKEN, 10-12 June 2008), We have carried out detailed investigations of the long term X-ray flux variations of the high mass X-ray binary pulsar Cen X-3 using archival X-ray data from the Rossi X-ray timing Explorer (RXTE). In the lightcurves of several observations made with the Proportional Counter Array (PCA) and covering a wide range of X-ray intensity, we have detected Quasi Periodic Oscillation (QPO). We have observed a clustering of the QPO peak frequency at 40 and 90 mHz with no dependence of the QPO frequency and occurrence of QPOs on the X-ray intensity. If the observed X-ray intensity of Cen X-3 and its long term variations are related to the mass accretion rate, the lack of QPO frequency variation of Cen X-3 is in contrast with an inner disk origin of the QPOs. Using the same RXTE-PCA observations, we have also measured the pulsed flux of Cen X-3 in different flux states. We found that below a certain flux level, the X-ray lightcurve does not have any pulsations while above this level, the pulsed flux increases linearly with the peak flux. This is consistent with the X-ray emission of Cen X-3 having one unpulsed component and one varying component with a constant pulsed fraction. In the low state, the unpulsed component becomes dominant. The detected X-ray emission in the low state can be due to scattering of X-rays from the stellar wind of the companion star. We have also studied the orbital modulation of the Cen X-3 X-ray lightcurve using the long term X-ray lightcurve made with the All Sky Monitor on board the RXTE. We found an evolution of the orbital modulation of the X-ray lightcurve as a function of the flux state. In high state, the transitions are sharp indicating that most of the observed X-rays are produced in a small region. In the low state, the orbital modulation is smooth, indicating that most of the observed X-rays are produced in an extended region, probably by scattering of X-rays from a hidden central source. The QPO measurements, the pulsed flux measurements and the orbital modulation measurements indicate that the different flux states of Cen X-3 are produced by different degree of absorption. We propose that the absorption is caused by a periodically precessing accretion disk., 資料番号: AA0064306022, レポート番号: JAXA-SP-08-014E},
 pages = {102--107},
 publisher = {宇宙航空研究開発機構, Japan Aerospace Exploration Agency (JAXA)},
 title = {Long term X-ray intensity variations of Cen X-3},
 volume = {JAXA-SP-08-014E},
 year = {2009}
}