Can I use AT TINY48 as a board in arduino?

I have seen people using at tiny 45 and other boards and there are hardware configurations files for them. Can we use AT Tiny48 as a processor for arduino?

if so where can I get a boards.txt file that supports it? Alternatively how can I write such a file.

Your best bet is to download a suitable core for this processor. Maybe something like this though I'm sure there are others.

Why Tiny48?

The TCWORLD fork of the tiny core supports x7, x8, x61 tiny's, in addition to the usual x4 and x5's.