I am a non-resident alien as per US IRS definition. I generate some income from the US on account of book royalties and advance from a U.S. publisher. I am otherwise employed full-time in India and file my tax returns in India. Do I need to additionally file returns in the U.S? If so, is there a minimum income slab below which returns don't need to be filed in this case?
In the first few pages of the 1040NR instructions for each year, there is a section called "Who Must File". That will answer your question.