The scientific payload

The scientific instruments of BeppoSAX ([Boella et al. 1997a,Piro et al. 1995,Scarsi 1993]) can be classified in Narrow Field Instruments (NFI) and Wide Field Instruments (WFI). The NFI consists of a Low Energy Concentrator Spectrometer (LECS, 0.1-10 keV), three Medium Energy Concentrator Spectrometers (MECS, 2-10 keV), a High Gas Pressure Scintillator Proportional Counter (HPGSPC, 20-120 keV), a Phoswich Detection System (PDS, 15-300 keV), all pointing along the satellite +Z axis. The WFI consists of two Wide Field Cameras (WFC, 1.5-26 keV), pointing along the +Y (WFC2) and -Y (WFC1) axis, and the GRBM, whose detectors axis are co-aligned with the $\pm$X and $\pm$Y satellite axis. The geometry of the BeppoSAX payload is shown in Fig. 1.3

  

Figure 1.3: BeppoSAX scientific payload

 

 

Instrument Detecting Band FOV Ang. res. Eff. Area Energy Re.

$$^{\circ}$$ units^(a) (keV) (arcmin) (cm²) (% FWHM)

LECS 1(+Z) 0.1-10 0.5 3.5@0.25 keV 22@0.25 keV 8x(E/6)^-0.5

MECS 3(+Z) 1.3-10 0.5 1.2@6 keV 150@6 keV 8x(E/6)^-0.5

HPGSPC 1(+Z) 4-120 1.1 collimated 240@30 keV 4x(E/60)^-0.5

PDS 1(+Z) 15-300 1.3 collimated 600@80 keV 15x(E/60)^-0.5

WFC 2(-Y,+Y) 1.5-26 20x20 3 140@10 keV 18x(E/6)^-0.5

$$\pm \pm$$ GRBM^(b) 40-700 open - 500@300 keV 30x(E/100)^-0.4

• [^(a)] The directions of the detectors axis are reported between parenthesis
• [^(b)] For the GRBM we report effective area and energy resolution for unit 1; the determination of this values is discussed in chapter 3.

The LECS ([Parmar et al. 1997]) and MECS ([Boella et al. 1997b]) units all consists of grazing incidence X-ray concentrators, composed of 30 nested Nickel Au coated coaxial and co-focal mirrors with a double cone approximation to Wolter I geometry, and of a gas scintillation proportional counter using Xenon at about 1.0 atm. The MECS make use of a 50 $\mu$m beryllium window , while the LECS window, in order to extend the energy band down to 0.1 keV, is made of 1.25 $\mu$m of Polymide, 0.035 $\mu$m of aluminum nitride and 0.044 $\mu$m of Al. The support structure of the concentrators is made of carbon fiber tubes an each pair of tubes is contained in a 2cm thick Al box.

The HPGSPC ([Manzo et al. 1997]) is an high pressure scintillator proportional counter filled with a 5 atm gas mixture (90% Xe and 10% He). The gas cell is cylindrical and made of a Titanium body 3 mm thick and with a diameter of 360 mm and a depth of 184.5 mm. The entrance window is made of two Beryllium foils 0.5 and 0.8 mm thick and has a diameter of 30 cm.

The WFC ([Jager et al. 1997]) consist of two coded aperture cameras, with detector and mask of the same size, about 25.6 x 25.6 cm². The mask is made of Iron and is located 0.7 m away from the detector, which is a multi wire proportional counter filled with a gas mixture (94% Xe, 5% CO₂, 1% He) and with an entrance window made of Beryllium 150 $\mu$m thick. The gas cell is made of Titanium coated with 1 mm of Al, and the mask and the detector are supported by a stainless steel structure. The FOV of the WFC is 20$\rm ^{\circ}$ X 20$\rm ^{\circ}$ FWHM (40$\rm ^{\circ}$ x 40$\rm ^{\circ}$ at zero response).

Finally, The PDS is described in section 1.2, where we outline in detail the GRBM experiment.

The main detecting characteristics of the instruments are reported in Tab. 1.1.