MBTA track maintenance car in Portland?

I'm on an Amtrak train in Portland right now. On the adjacent track is a yellow MBTA maintenance vehicle, T-87213. It seems to have a generator or compressor of some sort on it.

Does anyone know what it's doing here?

Possibly the MBTA wash train? Have a tank car nearby? The last few years the T has loaned their wash train to Pan Am / Amtrak to wash the Brunswick branch toward the end of slippery rail season. The mainline has enough tonnage to not worry about washing, but Royal Jct. to Brunswick can get pretty slick.