Chandra observations of variable embedded x-ray sources in orion. I. Resolving the Orion Trapezium

We used the High-Energy Transmission Grating Spectrometer on board the Chan dra X-Ray Observatory to perform two observations, separated by 3 weeks, of the Orion Trapezium region. The zeroth-order images on the Advanced CCD Im aging Spectrometer provide spatial resolution of and 0.5" moderate energy r esolution. Within a 160" x 140" region around the Orion Trapezium, we resol ve 111 X-ray sources with luminosities between 7 x 10(28) and 2 x 10(32) er gs s(-1). We do not detect any diffuse emission. All but six sources are id entified. From spectral fits of the three brightest stars in the Trapezium, we determine the line-of-sight column density to be N-H = (1/93 +/- 0.29) x 10(21) cm(-2). Many sources appear much more heavily absorbed, with N-H i n the range of 10(22)-10(23) cm(-2). A large fraction of sources also show excursions in luminosity by more than a factor 5 on timescales greater than 50 ks; many are detected only in one of the observations. The main objecti ve of this paper is to study the Orion Trapezium and its close vicinity. Al l five Trapezium stars are bright in X-rays, with theta (1) Ori C accountin g for about 60% of the total luminosity of the Trapezium. The CCD spectra o f the three very early-type members can be fitted with a two-temperature th ermal spectrum with a soft component of k(T) similar to 0.8 keV and a hard component of k(T) similar to 2-3 keV. theta (1) Ori B is an order of magnit ude fainter than theta (1) Ori E and shows only a hard spectrum of k(T) sim ilar to 3 keV. theta (1) Ori D is another order of magnitude fainter than t heta (1) Ori B, with only a kT similar to 0.7 keV component. We discuss the se results in the context of stellar wind models. We detect eight additiona l, mostly variable X-ray sources in the close vicinity of the Trapezium. Th ey are identified with thermal and nonthermal radio sources, as well as inf rared and optical stars. Five of these X-ray sources are identified with pr oplyds, and we argue that the X-ray emission originates from class I, II, a nd III protostars at the cores of the proplyds.