Manoj Yadav, the accused, allegedly committed the crimes last night.
He was arrested today from Parahia village under Nadiganj police station, they said.
A pistol and 11 ammunition were seized from his possession, they added.
Raids were being carried out to nab Manoj's father Rameshwar Yadav, who, too has been named as an accused in the assault case.
The rape victim has been taken to a government hospital for medical test, they said.