We present the results of a 200 ks Chandra observation of part of the Groth Strip region , using the ACIS-I instrument .
We present a relatively simple method for the detection of point-sources and calculation of limiting sensitivities , which we argue is at least as sensitive and more self-consistent than previous methods presented in the literature .
158 distinct X-ray sources are included in our point-source catalogue in the ACIS-I area .
The number counts show a relative dearth of X-ray sources in this region .
For example at a flux limit of 10 ^ { -15 } erg cm ^ { -2 } s ^ { -1 } around 20 per cent more soft band sources are detected in the HDF-N and almost 50 per cent more in the ELAIS-N1 field , which we have analysed by the same method for comparison .
We find , however , that these differences are consistent with Poisson variations at < 2 \sigma significance , and therefore there is no evidence for cosmic variance based on these number counts alone .
We determine the average spectra of the objects and find a marked difference between the soft-band selected sources , which have \Gamma = 1.9 typical of unobscured AGN , and the hard-band selected sources , which have \Gamma = 1.0 .
Reassuringly , the sample as a whole has a mean spectrum of \Gamma = 1.4 \pm 0.1 , the same as the X-ray background .
Nonetheless , our results imply that the fraction of sources with significant obscuration is only \sim 25 per cent , much less than predicted by standard AGN population synthesis models .
This is confirmed by direct spectral fitting , with only a handful of objects showing evidence for absorption .
After accounting for absorption , all objects are consistent with mean intrinsic spectrum of \Gamma = 1.76 \pm 0.08 , very similar to local Seyferts .
The survey area is distinguished by having outstanding multi-waveband coverage .
Comparison with these observations and detailed discussion of the X-ray source properties will be presented in future papers .