A 5.57 hour modulation of the X-ray flux from 4U 1822-37.
Abstract
The X-ray flux of 4U 1822-37 is shown to be modulated with the 5.57 hr period of its optical counterpart. The X-ray light curve is two component, with a smooth sinusoidal-like 25% semiamplitude modulation and a 30 minute dip of approximately 0.2 in phase following the other minimum; the dip center occurs 0.04 in phase after the optical minimum. The X-ray spectrum is a relatively flat power law up to 17 keV, above which it steepens; iron emission is detected at 6.7 keV with a 4 keV FWHM and an equivalent width of 1100 eV. An excess below 2 keV is consistent with either a 0.25 keV thermal component of 350 eV equivalent width iron L emission. Modeling the eclipse for a 0.5-0.7 solar radius companion gives a system inclination of 70-79 deg and a spherical cloud radius of 0.2-0.3 solar radius. Models for the long-term modulation are considered, and a comparison of the properties of 4U 1822-37 with those of Cyg X-3 shows that they are similar systems.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 1981
- DOI:
- 10.1086/159109
- Bibcode:
- 1981ApJ...247..994W
- Keywords:
-
- Binary Stars;
- Blue Stars;
- Modulation;
- Stellar Radiation;
- X Ray Sources;
- Heao 1;
- Light Curve;
- Stellar Magnitude;
- X Ray Spectra;
- Astronomy