Evidence for a 39-d period in Cyg X - 1
Abstract
THE detection of a 39-d period in Cyg X - 1 (HDE226868), as seen in the ultraviolet (ultraviolet-filter) polarisation1, would have at least one interesting interpretation, that of a third-body orbital period (M. Milgrom and J. Shaham, personal communication). We report here the result of long-term monitoring of the optical polarisation of Cyg X - 12, which has been in progress since 1974 at Pine Mountain Observatory, Oregon. Up to early August 1977, over 225 nights of ultraviolet-filter data were obtained. Power spectra of the ultraviolet-filter polarisation computed in March 1977 suggested a peak at the approximate period 39 d, common to the separate power spectra of our two instrumental Stokes parameters2 Q and U. The amplitude of the feature corresponds to a peak-to-peak polarisation variation of about 0.25%. The Q and U variations proved to be coherent with each other and to be of a rectilinear type, describable as a simple variation along a certain rotated Stokes parameter Q0, defined approximately by Q0=p cos[2(θ - 117°)]. The normalised conjugate parameter U0=p sin[2(θ - 117°)] shows no significant variation at the 39-d period.
- Publication:
-
Nature
- Pub Date:
- November 1977
- DOI:
- 10.1038/270227a0
- Bibcode:
- 1977Natur.270..227K
- Keywords:
-
- Cygnus Constellation;
- Periodic Variations;
- X Ray Sources;
- Polarization Characteristics;
- Power Spectra;
- Ultraviolet Astronomy;
- Ultraviolet Filters;
- Astrophysics