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the phoswich detection system ( ) is one of the narrow field instrument aboard the x  ray astronomy satellite , a program of the italian space agency ( asi ) with dutch participation @xcite .
a detailed description of the instrument can be found in @xcite .
the  was designed to operate in the hard x  ray range from 15 to 300 kev and to perform high sensitivity spectroscopic and temporal studies of celestial x 
ray sources , in particular their continuum emission .
classes of sources accessible to  include high mass x  ray binaries
( hmxrb ) , low mass x  ray binaries ( lmxrb ) , am her  type sources , supernova remnants ( in particular crab - like sources ) and active galactic nuclei ( agn ) .
in this paper we report on functional performance of  and on some scientific results obtained from the observation of different classes of x  ray sources performed during the science verification phase ( svp ) of the satellite .
was launched from cape canaveral with an atlas - centaur rocket on april 30 , 1996 .
its orbit is almost equatorial ( 3.9@xmath0 ) at an altitude of 600 km . during the  commissioning phase ( 1 may30 june 1996 ) , the  was switched on and tested . since then all subsystems continue to properly operate with very good performance .
the anticoincidence ( ac ) shields provide a reduction of the background level by about a factor two with respect to the level obtained with the phoswich technique alone .
in addition , the ac system strongly decreases the background modulation along the  orbit .
the background level @xmath1 of the  is the lowest obtained thus far with high energy instruments at satellite orbits , specially at energies beyond 100 kev . in the 15300 kev band
, @xmath1 is about @xmath2 cts  @xmath3  sec@xmath4  kev@xmath4 : this is @xmath5% of that published in the  handbook @xcite . in 100300
kev @xmath1 is a factor 3 lower than that expected .
the background modulation along a single  orbit and on one day time scale is about 20% , while longer term variations ( _ e.g. _ , build - up effects ) are negligible .
we evaluated the systematic error in the background subtraction introduced by the rocking collimator technique , by computing the background level variation between the on- and off - source positions in 32 ksec observing time .
we obtained @xmath6 mcrab in the 15300 kev energy band , corresponding to a 5@xmath7 instrument sensitivity of 0.9 mcrab .
this has to be compared to the value of 0.5 mcrab , if only poisson statistics is taken into account .
we will discuss some scientific results obtained with  during the  svp , that show the actual spectral and timing capability of the instrument in flight .
the source has been observed for calibration purposes two times , in september 1996 ( obs.i ) and in april 1997 ( obs.ii ) .
the spectral deconvolution makes use of a response function derived from a monte carlo code that describes the interaction of a photon beam with the  instrument , complemented by the ground calibrations @xcite .    by fitting the total spectrum of crab with a single power law model we obtained a photon index @xmath8 consistent for both observations : @xmath9 for obs.i and @xmath10 for obs.ii .
the normalization parameters at 1 kev are @xmath11 and @xmath12 for obs.i and obs.ii , respectively .
the fitting was not so good : the reduced @xmath13 was 2.89 ( 77 dof ) for obs.i and 3.09 ( 67 dof ) for obs.ii .
these high @xmath13 are partly due to a break in the crab high energy spectrum also observed by other groups @xcite , and partly to wiggles in the count rate spectrum between 30 and 60 kev , whose instrumental origin is under investigation .
these systematic effects are estimated to be less than 5% in the residuals and less than 1% in the spectral index reconstruction .
we can conclude , from these results , that the photon index is consistent with previous results on the source spectrum @xcite , while the normalization parameter is about 10% lower than the extrapolation of the power law spectrum measured with the mecs instrument @xcite aboard .
it is however consistent with published results on crab @xcite within their uncertainties .
this classical x  ray pulsar , belonging to the class of hmxrbs , was observed for @xmath14 sec during a low intensity level ( 30 mcrab ) at high energies .
the source was clearly detected up to about 50 kev .
the hard x  ray spectrum of the source is consistent with an optically thin thermal bremsstrahlung with @xmath15 kev and normalization parameter @xmath16 .
the plasma temperature and flux level are consistent with those measured by heao1/a4 @xcite .
the  pulse profile of the pulsar ( @xmath17 sec ) is characterized by a dip ( see fig .
[ cenx3 ] ) .
it appears different from the average pulse profiles previously reported @xcite .
an investigation on the origin of this different behavior is under way
.      this x  ray pulsar ( @xmath18 sec ) is one of the few lmxrbs that show pulsed emission .
it was detected with  up to 50 kev in @xmath5 ksec exposure time .
the spectral analysis is in progress , while the pulse profiles of the pulsar in two hard x  ray ranges are shown in fig .
as can be seen , 4u162667 exhibits a sinusoidal shape and a peculiar feature : the hardness ratio between 3050 kev and 1030 kev pulse profiles turns out to be anti - correlated with the intensity profile ( fig .  [ 1626]b ) .
pks2155304 is one of the strongest bl lac objects in the 210 kev energy band .
it is the first time the source has been simultaneously observed in a broad - energy band ( 0.1300 kev ) , crucial for studying the relationship among different emission components .
the source was clearly detected by  up to 100 kev ( exposure time @xmath19 ksec ) .
the ratio between the source spectrum and the crab spectrum is shown in fig .
it is apparent that the source spectrum is softer than crab below 1020 kev , while it is harder or similar to the crab spectral slope above 1020 kev .
an extended paper on the  results on this source can be found elsewhere @xcite .
the high energy experiment  is one of the narrow field instruments aboard the x  ray astronomy satellite . 
 it covers the energy band from 15 to 300 kev . here 
 we report results on its in - flight performance and observations of galactic and extragalactic x  ray sources obtained during the science verification phase of the satellite : in particular crab , cen  x3 , 4u162667 and pks2155305 .