Letter | Published:

Limit on the Angular Size of Cyg XR–1

Nature volume 222, page 967 (07 June 1969) | Download Citation

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Abstract

BOTH nebular and stellar objects have been identified as discrete sources of cosmic X-rays. Representative of the first is the Crab Nebula, the size of which has been measured to be 1 to 2 arc min in the energy range 1–6 keV according to observations during a lunar occupation1 and with a modulation collimator2. This size is comparable with the optical size of the nebula. Representative of stellar sources is Sco X–1, the X-ray size of which has been shown to be less than 20 arc s by a measurement with a modulation collimator, also in the energy range 1–6 keV (ref. 3). The optical counterpart of Sco X–1 is an irregularly variable blue star4. The tentative identifications of Cas XR–1 with the supernova remnant, Cas A (ref. 5, and of several other X-ray sources with blue stars (Cyg X–2 (ref. 6), Cen XR–2 (ref. 7)) obviously suggest that these particular sources can be assigned to the nebular and the stellar classes, respectively.

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Author information

Author notes

    • FRANKLIN W. FLOYD

    Present address: MIT Lincoln Laboratory.

Affiliations

  1. Center for Space Research, Massachusetts Institute of Technology.

    • FRANKLIN W. FLOYD

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DOI

https://doi.org/10.1038/222967a0

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