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Astron. Astrophys. 349, 88-96 (1999)

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2. Data reduction

We used ROSAT all-sky survey (RASS) data as well as archival and serendipituous pointed observations of the galaxies. The observations are summarized in Table 1.


Table 1. Log of observations. [FORMULA] gives the exposure time. If `surv' is listed in the column `instrument' this refers to RASS data taken with the PSPC. RASS observations were performed during Aug. 1990 - Jan. 1991.
1) countrate in the observed (0.1-2.4) keV band (note the different sensitivity of the PSPC and HRI detector, which results in a countrate conversion of a factor of several from one instrument to the other, depending on the spectral shape).

For further analysis of the pointed PSPC and HRI data the source photons were extracted within a circular cell centered on the target source. The background was determined in a source-free region around the target source and subtracted. The data were corrected for vignetting and dead-time, using the EXSAS software package (Zimmermann et al. 1994).

To carry out the spectral analysis source photons in the amplitude channels 11-240 were binned according to a constant signal/noise ratio of [FORMULA] 4[FORMULA].

Lightcurves were created with a binning of 800 sec to account for the wobble mode of the satellite.

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© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999