No worries. I have not played another 40K RPG. Deathwatch is my one and only... so far.
And as such, I do not know by heart what Unarmed Master grants. I would guess it negates any penalties to fighting without a weapon and helps solidify the Killing Machine image of Astartes.
It's listed in DW actually. In addition to removing penaltis for fighting unarmed, normally unarmed attacks do 1d5-3 damage. Unarmed Warrior raises this to 1d10-3, Unarmed Master to 1d10.