The ROSAT All-Sky Survey (RASS) provides a unique source of information on the X-ray sky at 0.1 to 2.4 keV. The main part of the RASS was carried out in 1990 and 1991 with the Position Sensitive Proportional Counter (PSPC) as the focal instrument and with ROSAT being in scan mode. A small fraction of the sky remained with little or no exposure after the main RASS (40 / 170 / 460 deg2 with exposure times of 0 s / less than 50 s / less than 100 s). Figure 1 shows the main RASS countrate image (raw data) of a region with radius 93° , centered on ecliptical coordinates (lambda,beta) = (318°, 0°), covering all low exposure regions; regions with no exposure are indicated in light blue.
In February 1997 the PSPC was switched on for 4 weeks after a hibernation period of 2.5 years in order to perform a number of important observations and to complete the RASS. Since the ROSAT scan mode is no longer available, the observations had to be performed in the pointed mode. The PSPC was used as focal instrument in order to obtain data of similar quality as the already existing RASS data. More than 500 short pointings were scheduled, thus covering each point of the low-exposure regions with off-axis angles better than 30 arcmin. In Figure 2 each of these pointings is indicated by a circle (green and yellow circles: successfully observed; red circles: observation failed).
The new data included, ROSAT has now observed each point in the sky with at least 30 s exposure time, with the exception of one square degree around the strong source Sco X-1, which would destroy the PSPC upon exposure. Figure 3 shows the RASS countrate image after the inclusion of the new data. Future work will incorporate the new RASS data into the RASS source catalogue, and into the RASS diffuse soft X-ray sky maps.
Figure 1 Figure 2 Figure 3