Hiberfil

I have in drive C: a large file named hiberfil.sys (about 1Gb).
I thought at first it is a file constituted when I made my computer hibernate.
But I did not hibernate my computer for a certain time now and the hiberfil.sys file is quite recent.
Moreover, I booted on another disc, deleted the hiberfil.sys file on the old disc, but when I reboot on the old disc again it returns!
Could anyone tell me what file the hiberfil is and if I can and how get rid of it? It takes my precious disc realt estate.
Thank you