We report on sensitive far–infrared observations of ^ { 12 } CO pure rotational transitions in the OMC–1 core of Orion .
The lines were observed with the Long Wavelength Spectrometer ( LWS ) in the grating mode on board the Infrared Space Observatory ( ISO ) , covering the 43–197 \mu m wavelength range .
The transitions from J _ { up } = 14 up to J _ { up } = 19 have been identified across the whole OMC–1 core and lines up to J _ { up } = 43 have been detected towards the central region , KL/IRc2 .
In addition , we have taken high–quality spectra in the Fabry–Perot mode of some of the CO lines .
In KL/IRc2 the lines are satisfactorily accounted for by a three–temperature model describing the plateau and ridge emission .
The fluxes detected in the high– J transitions ( J _ { up } > 34 ) reveal the presence of a very hot and dense gas component ( T = 1500 - 2500 K ; N ( CO ) = 2 \times 10 ^ { 17 } \hbox { \kern 2.0 ptcm$ { } ^ { -2 } $ } ) , probably originating from some of the embedded sources previously observed in the H _ { 2 } near–infrared lines .
At all other positions in the OMC–1 core , we estimate kinetic temperatures \geq 80 K and as high as 150 K at some positions around IRc2 , from a simple Large–Velocity Gradient model .