The four men allegedly raped the widow near a railway yard in the Kapa area on December 23, the officer said.
The accused - Suresh Sahu (24), Harish Chandrakar (25), Trinath Mahanand (24) and Vinay Yadav (24) - were arrested yesterday, he said.
As per the preliminary investigation, the woman, who works at a hotel, was in a relationship with Sahu. He took her to a deserted place in the Kapa area and allegedly raped her, the officer said.
The three accused also threatened the woman with dire consequences if she disclosed the incident to anyone, he said.
The victim reached the Pandri Police Station to file a complaint on Sunday, following which a case under Section 376 (rape) of the Indian Penal Code was registered, he said adding that a probe was on.