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Astron. Astrophys. 364, 165-169 (2000)

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4. X-ray and VHE gamma ray correlations

Cen X-3 is a strong but variable X-ray emitter. For example, the average daily rates for X-rays detected with the RXTE /ASM during 1997 and 1998 range from 0 to 32 counts [FORMULA]; the data are variable on a time scale of days. The daily average for the RXTE /ASM count rates are available for 22 of the 23 days when VHE gamma ray observations were made 1.

The strength of pulsed X-ray emission was also available as a daily average from the BATSE archive for 1997 2; during the 1998 and some of the 1999 VHE observations, the X-ray flux was below the threshold for BATSE detection. The BATSE data provide a series of independent X-ray measurements, including a measurement on the single day of the TeV gamma ray observations for which there is no corresponding RXTE /ASM measurement.

The VHE gamma ray signal plotted on a day by day basis is shown in Fig. 1b. There is no evidence for outbursts of TeV gamma ray emission on a timescale of days and the data are consistent with a constant VHE gamma ray flux ([FORMULA], 22 df).

In Fig. 2a we show the relation between the count rate of the RXTE /ASM data and our gamma ray signals. In Fig. 2b we show a similar plot relating the individual BATSE pulsed X-ray fluxes and our gamma ray signals. We have no formal evidence for a correlation, although it is interesting to note that the day of highest detected gamma ray flux coincides with the day of most X-ray activity in the dataset (1997 March 4).

[FIGURE] Fig. 2a and b. The relation between the daily VHE gamma ray flux from Cen X-3 and a the X-ray flux detected by ASM/RXTE and b the X-ray pulsed flux detected by BATSE.

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© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000