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Astron. Astrophys. 321, 776-790 (1997)

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2. Observations

The data we used in this paper were obtained with the Large Area Counter (LAC, Turner et al. 1989) on board of the Ginga satellite (Makino et al. 1989). The first data were obtained on May 23, 1989 and the last data almost 160 days later on November 1. For a log of the observations we refer to Tables 1 and 2.

The observations can be divided into two parts: one with as high a time resolution as possible, uncorrected for dead time, background, and collimator response, which is used for the timing analysis, and another with a moderate time resolution (usually 4 seconds) with high spectral resolution and corrected for dead time, background, and collimator response, which is used for the spectral analysis.

The properties of the data we used are also summarized in Tables 1 and 2. It should be noted that these two data sets show overlap. Some data which have been obtained at high time resolution (especially MPC3 and MPC2 mode data) have also been corrected for background, aspect and dead-time and rebinned in time to make them suitable for inclusion in the CDs and HIDs.


[TABLE]

Table 1. Log of the observations used for the corrected data.



[TABLE]

Table 2. Log of the observations used for the high time resolution data.


The data can be further divided into a part taken on May 30, 1989 (1989 day 150) when the source was extremely bright, with dead time corrected count rates up to [FORMULA] cts/s, already described in some detail by Oosterbroek et al. (1995), and all other data, in which those extreme count rates are not reached. Those very high count rates require special precaution in the data analysis, and because the source behaviour on May 30 is different from that during the other observations, the May 30 data will be described mostly separately. During those early observations source variations are very dramatic and irregular. (Note that the peak rate in Fig. 1 of Tanaka, 1989, is about a factor 3 higher; this is caused by the higher time resolution employed in that figure, in combination with the extreme rapid variability of the source, and a different energy range (1-37 keV vs. 2.3-23 keV).)

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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