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We present the first images of the 28SiO v=1, J=2-1 maser emission around theclosest known massive young stellar object Orion Source I observed at 86 GHz(3mm) with the VLBA. These images have high spatial (~0.3 mas) and spectral(~0.054 km/s) resolutions. We find that the 3mm masers lie in an X-shaped locusconsisting of four arms, with blue-shifted emission in the south and east armsand red-shifted emission in the north and west arms. Comparisons with previousimages of the 28SiO v=1,2, J=1-0 transitions at 7mm (observed in 2001-2002)show that the bulk of the J=2-1 transition emission follows the streamlines ofthe J=1-0 emission and exhibits an overall velocity gradient consistent withthe gradient at 7mm. While there is spatial overlap between the 3mm and 7mmtransitions, the 3mm emission, on average, lies at larger projected distancesfrom Source I (~44 AU compared with ~35 AU for 7mm). The spatial overlapbetween the v=1, J=1-0 and J=2-1 transitions is suggestive of a range oftemperatures and densities where physical conditions are favorable for bothtransitions of a same vibrational state. However, the observed spatial offsetbetween the bulk of emission at 3mm and 7mm possibly indicates different rangesof temperatures and densities for optimal excitation of the masers. We discussdifferent maser pumping models that may explain the observed offset. Weinterpret the 3mm and 7mm masers as being part of a single wide-angle outflowarising from the surface of an edge-on disk rotating about anortheast-southwest axis, with a continuous velocity gradient indicative ofdifferential rotation consistent with a Keplerian profile in a high-massproto-binary.

VLBA imaging of the 3mm SiO maser emission in the disk-wind from the massive protostellar system Orion Source I