A deep ROSAT PSPC image centred on the Orion Trapezium has revealed that most of the X-ray emission originates from discrete sources, in contrast to previous EINSTEIN data which suggested a diffuse emission component. We present a list of 171 X-ray sources all situated in the so-called inner ring of the field of view (20' radius). The field is crowded with sources. A special procedure had to be developed to cope with the severe blending of sources. The present list is not complete for L_X_<3.5*10^29^erg/s due to this reason and many more sources can still be expected by a next step in the reduction. Nearly all of the sources could be identified with pre-main sequence stars of the Ori OB 1 association in its subgroups Ic and Id. The statistics of this ensemble are discussed. It seems that members of the above subgroups can be distinguished on the basis of an additional amount of X-ray extinction seen in their spectra or hardness ratios. The O stars in the area ({teta}1 Ori C, {teta}2 Ori A and {iota} Ori) are briefly discussed. Six B stars are identified with X-ray sources.
A deep ROSAT PSPC image centred on the Orion Trapezium has been reduced a second time using an improved version of the PSF to fit the data. The outer rim of the field of view was also included. The new catalogue contains 316 X-ray sources which are easily identified with pre-main sequence stars of the Ori OB1 Ic and Id association. All 316 sources were tested for variability. No variations were found inside the single exposures of about 45 minutes length each. Between the 4 exposures spaced over 5 days about 1/3 of the sources show signs of activities of various forms. As above 25% of these have somewhat regular lights curves (monotonically rising or falling or hill- shaped) we infer that at least some outbursts with time scales longer than a day are present and that past searches for X-ray flares of pre-main sequence stars were biased towards shorter time scales.
