It's never illegal to download a copyright file if you have the permission of the copyright owner, so it depends on where you find the e-book and the license terms, if any, under which it is made available for download.
By definition, pirating is illegal. If you download the book legally, you are not pirating it.
Section 60c permits copying only up to 75% of a work for personal research, with some exceptions for smaller works that presumably do not apply to monographs, so it would not permit the download you describe if the download would otherwise be forbidden.
Otherwise, a work of scientific research is no different from any other copyright-protected work. The author has a right to profit from the fruits of his or her labor.