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Science 14 August 1992:
Vol. 257. no. 5072, pp. 935 - 937
DOI: 10.1126/science.257.5072.935
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Articles

A Lunar Occultation of the Dust-Scattering Halo Around GX 5-1 Observed with ROSAT

Peter Predehl 1, Jürgen H. M. M. Schmitt 1, Steven L. Snowden 1, and Joachim Trümper 1

1 Max-Planck-Institut für extraterrestrische Physik, D-8046 Garching bei München, Germany

The x-ray source GX 5-1 in the galactic bulge has been observed with the position-sensitive proportional counter onboard the Röntgen satellite (ROSAT) during and after a lunar occultation. Extended emission around the source was unambiguously discovered while the central source was behind the lunar rim. This emission is interpreted as a dust-scattering halo around GX 5-1 that has a fractional intensity of 28 percent, implying a grain column density between GX 5-1 and Earth of sim3 x 1010 per square centimeter. The halo derived from imaging during the ROSAT all-sky survey is identical to that obtained from the lunar occultation, thus demonstrating that the ROSAT x-ray mirror scattering has not changed as compared with the mirror properties as measured in preflight calibrations.

Submitted on April 6, 1992
Accepted on June 12, 1992

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Science. ISSN 0036-8075 (print), 1095-9203 (online)