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The Scientific Instruments

In fig. [*] a sketched view of the scientific payload shows how the various instruments are placed.

Figure: The BeppoSAX Scientific Payload
\epsfig{file=neu_payload.eps, width=12.0cm}\end{center}\end{figure}

The instruments are grouped into two classes: the Narrow Field Instruments (NFIs) and the Wide Field Cameras (WFCs). All the NFIs are co-aligned and pointing along the positive direction of the Z axis of the BeppoSAX frame of reference; they consist of the following (Table [*]): a LECS (Low Energy Concentrator Spectrometer, $0.1-10$ keV), three MECS (Medium Energy Concentrator Spectrometers, $1.3-10$ keV), a HPGSPC (High Pressure Gas Scintillation Proportional Counter, $4-120$ keV), and a PDS (Phoswich Detection System, $15-300$ keV). Each imaging GSPC is located at the focal plane of an X-ray concentrator system. The WFCs ($2-28$ keV) consist of two identical coded mask cameras co-aligned with the Y axis: WFC1 points along the negative direction and WFC2 along the positive one.

Eventually, there is another instrument which, on principle, has no imaging capability: the Gamma-Ray Burst Monitor (GRBM), whose four detector units form a square well around the PDS: the normal directions to GRBM1 and GRBM3 point along the same directions as WFC1 (-Y) and WFC2 (+Y), respectively, while +X for GRBM2 and -X for GRBM4 (fig. [*]).

Table: Main features of the scientific instruments
Instrument Band FOV Ang. Res.$^{(1)}$ Eff. Area Energy Res. Time Res.
units (keV) (FWHM) (FWHM) (cm$^{2}$) (% FWHM) ($\mu$s)
1 LECS 0.1-10 37$^\prime$ 9.7$^\prime$@0.28 keV 22@0.28 keV $8.84$x$(E/6)^{-0.42}$ $16 \mu$s
      2.1$^\prime$@6 keV 50@6 keV    
      105 $^{\prime\prime}$@1.5 keV 31@1.5 keV    
3 MECS 1.3-10 28$^\prime$ 75 $^{\prime\prime}$@6.4 keV 150@6.4 keV $8$x$(E/6)^{-0.5}$ $15 \mu$s
      75 $^{\prime\prime}$@8.1 keV 101@8.1 keV    
1 HPGSPC 4-120 1.1$^\circ$ collimated 240@30 keV $4$x$(E/60)^{-0.5}$ $15 \mu$s
1 PDS 15-300 1.3$^\circ$ collimated 600@80 keV $15$x$(E/60)^{-0.5}$ $16 \mu$s
2 WFC 1.8-28 $20$$^\circ$x $20$$^\circ$ 3 140@10 keV $18$x$(E/6)^{-0.5}$ $0.5$ ms$^{(2)}$
4 GRBM$^{(3)}$ 40-700 open $-$ 500@300 keV $30$x $(E/100)^{-0.4}$ 1 s$^{(4)}$

Radius containing the 50% of the power.
Valid for imaging mode (Normal Mode). In the case of fast non-imaging mode (High Time Resolution Mode) it is 0.25 ms.
The effective area and the energy resolution refer to unit 1.
Valid for ratemeters (normal mode). High Time Resolution (HTR) mode reaches 7.8125ms and 0.488 ms, while the GRBM spectra's temporal resolution is fixed to 128 s.

The LECS ([Parmar et al., 1997]) and the MECS ([Boella et al., 1997b]) are a set of four X-ray concentrators, each one consisting of 30 nested, gold coated, confocal mirrors with a double cone approximation to Wolter I geometry ([Citterio et al., 1985,Conti et al., 1994]), with diameters ranging from $16.2$ to $6.8$ cm, thickness ranging from $0.4$ to $0.2$ mm, with a focal length of 185 cm and a geometric area of 124 cm$^2$. The detector unit, placed in the focal plane, is a position sensitive gas scintillation proportional counter and it is filled with Xenon ($1.0$ atm at 25 $^\circ$C). The gas cell has a cylindrical shape; at the top, the LECS is closed by different layers made of polymide, aluminum nitride, Al and carbon, allowing the detection of down to $0.1$ keV photons and shielding it against space plasma; in the case of the MECS, the top layer consists of a 50 $\mu$m beryllium window.

The HPGSPC instrument ([Manzo et al., 1997]) is a High Pressure Gas Scintillation Proportional Counter filled with a gas mixture of Xe (90%) and He (10%) at the pressure of 5 atm. Its gas cell is cylindrical and consists of a titanium body (3 mm thick, diameter of 360 mm and depth of 184.5 mm) closed by a beryllium entrance window, whose foils, $0.5$ and $0.8$ mm thick and with a diameter of 30 cm, are transparent down to 3 keV photons and, at the same time, stiff enough to withstand the gas pressure.

The WFCs ([Jager et al. 1997]) are two identical coded mask cameras working in the $1.8-28$ keV energy band: their FOV is $20$$^\circ$x $20$$^\circ$FWHM ($40$$^\circ$x $40$$^\circ$at zero response). The detector is a Multi Wire Proportional Counter filled with a gas mixture (94% Xe, 5% CO$_2$, 1% He, at 2.2 bar) and closed by a 150 $\mu$m thick entrance window of beryllium, while the coded mask, made of iron, is placed 70 cm in front of it; both are supported by a stainless steel structure and their sizes are $25.5$x$25.5$ cm$^2$ for the detector and $25.6$x$25.6$ cm$^2$ for the mask, respectively. The angular resolving power is 5$^\prime$FWHM, while the source location accuracy is better than 1$^\prime$, taking into account also the satellite pointing stability. The limiting sensitivity, though depending on the X-ray background flux, is a few mCrab in $10^5$ s.

The PDS is described in the following section, that is mainly devoted to the description of the GRBM structure and data.

next up previous contents
Next: The PDS and the Up: BeppoSAX Previous: Mission Outline   Contents
Cristiano Guidorzi 2003-07-31