Two State Police troopers patrolling the Esplanade broke up an apparent sexual assault in the area of the Longfellow Bridge early this morning, according to the Suffolk District Attorney Daniel F. Conley’s office.

The troopers arrested 49-year-old Joseph Barthel for indecent assault and battery, said Conley’s office.

The victim, an adult female, was transported to a local hospital and was not seriously physically injured, said Jake Wark, a spokesman for Conley.

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Wark said he did not believe the two knew each other but did not have details about the circumstance of the alleged assault.

He commended the troopers who broke up the assault, saying they did “really great work” and that “they were in exactly the right place at exactly the right time.”

The incident does not appear to be linked to the spate of unsolved sexual assaults on the Esplanade over the past few years, the district attorney’s office said in a release. The suspect involved does not match the description of alleged serial attacker, but the office said they would nonetheless compare the incidents to look for similarities.

Since 2007, police believe one at-large man is responsible for three similar sexual attacks, as well as a 2006 assault that took place at Joe Moakley Field in South Boston.

Authorities released a sketch of the suspect in 2008, describing him as a black man, clean-shaven and bald, between 5 foot 8 to 5 foot 10, with a muscular build.

Barthel is expected to be arraigned on Monday in Boston Municipal Court, Conley’s office said.