2001/03/22 by Jin‐Lu Qu, J. L. Qu, Wei Yu +2 · 1 citation
Earth and Planetary Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #High-pressure geophysics and materials #astro-ph
paper · pdf · doi:10.1086/321460
12 pages, 4 figures, accepted for publication in ApJ
arxiv created 2001/03/22 · openalex publication_date 2001/07/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/01
Earlier work showed that the track in the X-ray hardness-intensity diagram of Cir X-1 corresponds to a Z track in its color-color diagram. In this paper, we study the cross spectrum of Cir X-1 in different regions of the hardness-intensity diagram with RXTE /PCA data. Comparing the light curves of Cir X-1 for the energy band 1.8-5.1 keV with those for 5.1-13.1 keV, we find that Cir X-1 exhibits a hard time lag on the horizontal branch and a soft time lag on both the normal and the flaring branches. This indicates that Cir X-1 is similar to GX 5-1 and Cyg X-2 on the horizontal branch but is different from them on the normal branch. We briefly discuss the mechanism of the time lags in the context of Comptonization models.