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Astron. Astrophys. 339, 327-336 (1998)

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3. Beppo-SAX data reduction

Beppo-SAX (Boella et al. 1997a) is a major mission of the Agenzia Spaziale Italiana (ASI), with participation of the Netherlands Agency for Aerospace Programs (NIVR); it aims to study celestial sources in the wide X-ray band 0.1-300 keV. The scientific payload is constituted of a pair of gas scintillator proportional counters with imaging capabilities (Low Energy Concentrator Spectrometer, LECS, Parmar et al. 1997, sensitive in the 0.1-10 keV band; Medium Energy Concentrator Spectrometer, MECS, Boella et al. 1997b, sensitive in the 1.8-10.5 keV band), and a pair of collimated high-energy instruments (High Pressure Gas Scintillating Proportional Counter, HPGSPC, Manzo et al. 1997, sensitive in the 7-60 keV band; Phoswitch Detector System, PDS, Frontera et al. 1997, sensitive in the 13-200 keV band). The HPGSPC is more oriented to high-resolution spectroscopy of bright sources, while the PDS possesses an unprecedented sensitivity in its energy range (Guainazzi & Matteuzzi 1997).

Beppo-SAX observed 1H0419-577 on 1996 September 30, from 06:24:00 UT to 16:40:50 UT. The LECS was switched off during the whole observation due to technical problems. The other instruments were operating in direct modes, which provide full information on the arrival time, energy, burst length/rise time and - if available - position of each photon. Data have been reduced with the SAXDAS package (version 1.1) in the FTOOLS 3.5 environment. Standard selection criteria on satellite aspect quantities were applied to avoid Earth occultation (angle between the pointing direction and the Earth's limb [FORMULA]); South Atlantic Geomagnetic Anomaly (SAGA) passages; and particle contamination (momentum associated to the Geomagnetic cut-off Rigidity [FORMULA] GeV/c). In the MECS image, the source is nearly on-axis (offset angle [FORMULA]). MECS scientific products have been extracted from a circular area 3' radius around the apparent centroid of the source. Background spectra have been extracted from blank sky fields, using the same extraction region in detector coordinates as the source. Appropriate response matrices have been created, using the calibration files publicly available since 1997 January 31, which include the results of on-flight calibration. Total net MECS exposure time is [FORMULA] s and the corresponding count rate is [FORMULA] s-1 in the whole energy band. The spectrum has been rebinned in order to have at least 20 counts per channel, to ensure the applicability of [FORMULA] statistics. The source is not detected in the HPGSPC. PDS data have been further screened by eliminating 5 minute intervals after any SAGA passage, in order to avoid gain instabilities due to recovery to the nominal values after instrument switch off. The PDS was working in rocking mode, each collimator pointing alternatively every 96 seconds to the source and a field [FORMULA] aside. Short-lived ([FORMULA] s) spikes, due to particle "bursts" along the orbit, were also removed, according to the following procedure: bins in the 2-seconds binned light curves of each detector, whose count rate exceeded the mean by 5 standard deviations, have been excluded from the scientific product accumulation. Net exposure time in the PDS results [FORMULA] one half of the MECS ([FORMULA] s). In the 13-36 keV band the net background-subtracted count rate is [FORMULA] s-1; a typical systematic uncertainty of [FORMULA] s-1 in the whole 13-200 keV PDS band has been taken into account hereinafter. (Guainazzi & Matteuzzi 1997). The 13-36 keV detection is significant at the 5 [FORMULA] level.

Data analysis has been performed using the XANADU package. Hereafter energies are quoted in the source rest frame and errors are 90% confidence level for one interesting parameter (i.e. [FORMULA]), unless otherwise specified.

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© European Southern Observatory (ESO) 1998

Online publication: October 21, 1998
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