2. Data reduction
The observation was performed with the ROSAT PSPC from November 11 - 12, 1993, centered on NGC 4051. The total exposure time is about 12 ksec. The source photons were extracted within a circle chosen to be large enough to ensure that all of the source counts are included, given the detector response to very soft photons which causes an extension of the image below 0.2 keV (Nousek & Lesser 1993). The background was determined by removing all detected sources within the inner field of view. The data were corrected for vignetting and dead-time, using the EXSAS software (Zimmermann et al. 1994). The mean source countrate is about 2.9 cts/s. For the spectral analysis source photons in the amplitude channels 11-240 were binned according to a constant signal/noise ratio of 16 . For the temporal analysis the minimal binsize in time was 400 s to account for the satellite's wobbling motion.
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998