The dipping low-mass X-ray binary X1916-05 was observed with the large area proportional counters (LAC) on board Ginga. Although X-ray dips appeared every 50.00 min on the average, it was found that the recurrence period slightly varied on a time scale of 6 d. In association with the period change, the duration and depth of dips also varied on the same time scale. These time variations suggest dip properties with a period of 5--6 d. The energy spectrum during the dip was also investigated, and was found to be generally reproduced by a model spectrum comprising two components having the same intrinsic spectrum, but different regarding the degree of X-ray absorption from each other: one free and the other suffering from absorption. Based on a timing analysis, it is suggested that such a spectrum originates from a partial covering of the X-ray emission region by absorbing matter. Assuming that the absorbing matter is in Keplerian motion at the outer edge of the accretion disk, the size of the X-ray emission region was derived to be (1.2+/-0.9)*E(8) cm, 100-times larger than the radius of a neutron star, based on the mean value, 3.6+/-2.5 s, of the distribution of the ingress/egress time of the dips. This result suggests that the optically thin hot plasma around the neutron star extends out to 10(7) --10(8) cm distance from the center.
Publications of the Astronomical Society of Japan
- Pub Date:
- April 1995
- ACCRETION DISKS;
- STARS: INDIVIDUAL (X1916-05);
- X-RAYS: BINARIES