Detection of high-temperature plasma in the Orion Nebula - an intense 6.7-keV iron X-ray emission line in its spectrum

The X-ray spectrum of the Orion Nebula derived from observations made with the gas scintillation proportional counters onboard the Tenma satellite is described. The continuum spectrum is fitted well with a thermal bremsstrahlung model with kT = 3.7 ± 0.3 keV. An X-ray emission feature at an energy of 6.69 ± 0.06 keV having an equivalent width of 640 ±120 eV, which is attributed to transitions of Fe XXV ions, is clearly detected in the spectrum. It is suggested that the X-ray emission comes from an optically thin hot plasma at a temperature of 4 x 10 7 K. Possible origins of the high-temperature thermal component are briefly discussed