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Title:
A 5.57 hour modulation of the X-ray flux from 4U 1822-37
Authors:
White, N. E.; Becker, R. H.; Boldt, E. A.; Holt, S. S.; Serlemitsos, P. J.; Swank, J. H.
Affiliation:
AA(NASA, Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Greenbelt; Maryland, University, College Park, MD), AB(NASA, Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Greenbelt; Maryland, University, College Park, MD), AC(NASA, Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Greenbelt, MD), AD(NASA, Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Greenbelt, MD), AE(NASA, Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Greenbelt, MD), AF(NASA, Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Greenbelt, MD)
Publication:
Astrophysical Journal, Part 1, vol. 247, Aug. 1, 1981, p. 994-1002. (ApJ Homepage)
Publication Date:
08/1981
Category:
Astronomy
Origin:
STI
NASA/STI Keywords:
Binary Stars, Blue Stars, Modulation, Stellar Radiation, X Ray Sources, Heao 1, Light Curve, Stellar Magnitude, X Ray Spectra
DOI:
10.1086/159109
Bibliographic Code:
1981ApJ...247..994W

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.

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