Ginga observations of the LMXB X 1822-371 show that the broad orbital modulation and the eclipse are deeper at higher energies. This is explained if the X-ray emitting corona produces softer emission at greater heights from the disc plane, which suggests that either the corona is optically thick, or that the illuminating X-rays are anisotropic. Further investigation is hampered by an inadequate understanding of the X-ray spectrum of X 1822-371
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Hellier et al. (1992) studied this question.