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The Distance and Milliarcsecond Structure of Scorpius X-1
1998 Award Winner
Charles F. Bradshaw, The MITRE Corporation
E. B. Fomalont, National Radio Astronomy Observatory
B. J. Geldzahler, Institute for Computational Sciences and Informatics, Center for Earth Observing and Space Research
ABSTRACT
From three VLBA observations at 5 GHz, taken over 13 months, we have measured the trigonometric parallax of Sco X-1 as 0"00023 H 0"00028; hence, its distance is greater than 1300 pc. This supports the hypothesis that Sco X-1 radiates at or near the Eddington limit at the transition point between the normal and flaring branches of the X-ray color-color diagram. These results suggest that Sco X-1 and other Z-type quasi-periodic oscillators have a well defined luminosity and can be used as X-ray standard candles.
All three VLBA observations contain a radio core of flux density 0.5 mJy and size greater than 4 mas. However, the third VLBA observation revealed two additional radio components (separated by 12 mas and on opposite sides of the radio core) not present in the two previous observations. The evolution of these two components will remain unknown until multi-epoch radio imaging and coordinated radio and X-ray total flux density measurements can be made.
Publication
Published in May 1997. The Astrophysical Journal, Vol. 484, pp. L55-L58.
Additional Search Keywords
astrometry, radio continuum, stars, individual (Scorpius X-1), neutron, techniques, interferometric, X-rays
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