Simultaneous ROSAT/Ginga observations of 4U 1820-30

Details Simultaneous ROSAT/Ginga observations of 4U 1820-30 Simultaneous ROSAT/Ginga observations of 4U 1820-30

Feb 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.260..686v&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 260, no. 3, p. 686-692.

Astronomy and Astrophysics

Astronomy

31

Ginga Satellite, Light Curve, Rosat Mission, Stellar Orbits, X Ray Astronomy, X Ray Binaries, Spaceborne Astronomy, Stellar Models

Scientific paper

We have made simultaneous Ginga LAC and ROSAT PSPC observations of 4U 1820-30. The 685-s orbital light curves obtained with the two instruments are very similar, indicating that the energy dependence of the orbital modulation is small. Our measurements extend the baseline over which the period variations can be measured to 15 yr. The previous possibility, that the changes in the period are themselves periodic, with a period of about 8 yr, is no longer preferred over a constant P(dot). Over the interval 1976-91 the period has decreased, rather than increasing as predicted by the standard model for the orbital evolution of the binary. The average period derivative P(dot)/P was (-0.88 +/- 0.16) x 10 exp -7/yr, different by 11 sigma from the predicted value. Under the assumption that there are no intrinsic changes in the light curve that mimic a period change, we discuss three possible explanations.

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