Comment 1 for bug 1707979

Thanks for taking your time to report this issue and help making Ubuntu better.

Indeed, it looks like the ack package is currently missing from Artful. There is a proposed package though, but it doesn't seem to have made its way to the release archives. I took a look at the publishing history (click "View full publishing history" from the overview page or see https://launchpad.net/ubuntu/+source/ack/+publishinghistory) and looks like ack was recently removed from artful with the following comment:
"New version is broken according to autopkgtests, old version needs rebuilt for perl transition; remove to make room for perl"

Possibly these tests keep it from migrating from proposed.

(Btw, the ack-grep source package was replaced by ack recently, https://launchpad.net/ubuntu/+source/ack-grep/+publishinghistory)