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Astron. Astrophys. 342, 124-130 (1999)

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2. Observations and data reduction

The Italian-Dutch BeppoSAX X-ray observatory (Boella, Perola & Scarsi 1997a) carries four co-aligned NFI, which cover more than three decades of energy from 0.1 to 300 keV. These are:

In this paper results from the LECS, MECS and PDS instruments are presented, because the HPGSPC data could not provide any significant spectral constraint. The HPGSPC is actually tuned for spectroscopy of bright sources with good energy resolution, while the PDS possesses an unprecedented sensitivity in its energy band. Data were processed using the SAXDAS package (version 1.3.0). Publicly available response matrices (September 1997 release) were used.

For the imaging detectors, source spectra were extracted from regions of [FORMULA] and [FORMULA] radius, centered on the source positions in the LECS and MECS, respectively. Background spectra were extracted from blank sky fields. The background contributes less than 0.1% and 1% to the LECS and MECS full bandpass count rates of Mkn 421, respectively, and less than 10% in each energy channel even at the highest MECS bandpass energies. Background subtraction is therefore not critical for such a bright source.

PDS spectra were accumulated after excluding interval of source eclipse and each 5 minutes after a South Atlantic Geomagnetic Anomaly Passage, to avoid a gain instability due to recovery to the nominal crystal voltages after switch-on. PDS events were screened with a temperature-dependent Rise Time (RT) threshold, which allows a reduction by a factor of up to 50% of the instrumental background. Mkn 421 is detected at 8[FORMULA] level in the 13-30 keV band. All spectra were rebinned in order to have at least 20 counts per channel, to ensure the applicability of [FORMULA] statistics. In the following, energies are quoted in the source frame and uncertainties at 90% level of confidence for each parameter (i.e.: [FORMULA], Lampton, Margon & Bowyer 1976), unless otherwise specified.

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© European Southern Observatory (ESO) 1999

Online publication: December 22, 1998
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