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Astron. Astrophys. 353, 575-582 (2000)

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2. Observations

Results from the Low-Energy Concentrator Spectrometer (LECS; 0.1-10 keV; Parmar et al. 1997), and the Medium-Energy Concentrator Spectrometer (MECS; 1.8-10 keV; Boella et al. 1997) on-board BeppoSAX are presented. The MECS consists of two grazing incidence telescopes with imaging gas scintillation proportional counters in their focal planes. The LECS uses an identical concentrator system as the MECS, but utilizes an ultra-thin entrance window and a driftless configuration to extend the low-energy response to 0.1 keV.

The main-on state observation was performed during the trailing edge of the on-state, significantly later in [FORMULA] than the observation reported in O97. The 5.7 day duration short-on state observation covered most of the short-on state (and possibly some low-state at the end), but did not include the turn-on. The main-on state observation started at 1998 June 27 08:34 and lasted until June 28 02:56 (UTC). The short-on state observation lasted from 1998 July 9 20:38 until July 15 15:13 (UTC). Fig. 1 illustrates the [FORMULA] coverage of the three BeppoSAX observations of Her X-1 discussed here. The dashed line shows the mean 35 day 2-12 keV intensity profile obtained by folding the Rossi X-ray Timing Explorer (RXTE) All-sky Monitor (ASM) data obtained between 1996 February 20 and 1999 February 24 over the best-fit period of 34.75 days. The difference in [FORMULA] between the mid-times of the two observations discussed here is 0.43.

[FIGURE] Fig. 1. The mean 35 day intensity cycle of Her X-1 measured by the RXTE ASM. The phases, [FORMULA], of the Science Verification Phase (SVP) and AO2 main- and short-on state observations (AO2) are indicated

LECS and MECS data were extracted centered on the Her X-1 position using radii of 8´ and 4´, respectively. Good data were selected from intervals when the minimum elevation angle above the Earth's limb was [FORMULA]5o ([FORMULA]4o for the LECS) and when the instrument configuration was nominal using the SAXDAS 1.8.0 data analysis package. Spectral analysis was performed with the response matrix from the 1997 September release of SAXDAS for the MECS and a response matrix appropriate for the source position in the LECS field of view using LEMAT 3.5.6. The total main-on state exposures are 18 ks and 25 ks for the LECS and MECS, respectively. The total short-on state exposure times are 125 ks and 165 ks for the LECS and MECS, respectively.

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© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999