Sco X1 Lunar Eclipse
Credit: Max-Planck-Institut für extraterrestrische Physik, "Images from the X-ray sky with the ROSAT telescope", Feb 1999

Lunar Eclipse of Sco X-1

In the early days of X-ray astronomy it was thought that occultations of bright X-ray sources by the moon could allow astronomers to pinpoint the locations of the X-ray emitters and so identify them. The advent of imaging X-ray optics (first employed by the Einstein X-ray observatory, later by ROSAT) allowed astronomers to directly image cosmic X-ray sources; however, an eclipse lunar occultations can provide a finer measure of the spatial distribution of the X-ray emitting region around an X-ray source, just as eclipses of the sun by the moon can provide detailed information about the hottest emission regions in the solar atmosphere. However, lunar occultations of X-ray sources are relatively rare, and actually imaging such an event is rarer still. On Feb 20, 1998 the brightest X-ray source in the sky, Sco X-1 (a neutron star binary system) was eclipsed by the moon, and this event was captured by the ROSAT PSPC imager. The image above shows the source as the moon gradually moves in front of it. In the first column, after an exposure of a six degree distant comparison field the PSPC is switched off an pointed to Scorpius X-1. In the second column, simultanously with the start of the occultation the PSPC is switched on. The waning X-ray half Moon (red) is scrolling across the scattering halo of Scorpius X-1 (green) to the top right. Third column: During the flight through the radiation belt the the detector noise increases for a short time (blue). Fourth column: The observed constellation is outshined by the earth's atmosphere (yellow) before it goes down after all behind the earth's horizon.

The image above appeared in the 1999 ROSAT Calendar, produced by MPE. More such images can be found at the ROSAT Calendar Web page.

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Page Author: Dr. Michael F. Corcoran
Last modified June 23, 2000