Author(s)

Guoqiang Ding, Chunping Huang, Jinlu Qu

Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China.
University of Chinese Academy of Sciences, Beijing, China.
Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, China.

Using the data from the Proportional Counter Array on board theRossi X-Ray Timing Explorersatellite, we study the orbital modulation for the spectrum and mass accretion rate of Cir X-1 during its two orbital periods. We use a model consisting of a blackbody, a multicolor disk blackbody, and a line component to fit the spectrum and find that the spectrum is obviously modulated by the orbital phase. It is shown that the disk accretion rate in Cir X-1 undergoes three states during the orbital period. At the periastron with orbital phase 0-0.1, the disk accretion rate is sup-Eddington, then from phase 0.1 to the apastron (phase 0.5) it decreases dramatically and becomes near-Eddington, and from the apastron to the next periastron (phase 1) the disk accretion rate approximates Eddington and tends to be steady. We argue that the evolution of the disk accretion rate is attributed to the high orbital eccentricity of this source. The mass accretion rate onto the neutron star is much less than that onto the inner disk, indicating significant outflows in this source.

Accretion Disk; Compact Object; Neutron Star; Individual (Circinus X-1)

G. Ding, C. Huang and J. Qu, "The Orbital Modulation for the Spectrum and Mass Accretion Rate in Circinus X-1," International Journal of Astronomy and Astrophysics, Vol. 2 No. 4, 2012, pp. 256-265. doi: 10.4236/ijaa.2012.24033.