The detached adverbial modifier.

Any part of speech used in the function of an adverbial modifier may be detached, which accounts for the comma that separates it from the rest of the sentence.

The Corporal lit a pipe, carefully, because the enemy was close. (Heym)

In her excitement, Maria jammed the bedroom-door together. (London)

One summer, during a brief vacation at Knocke, his visit had come to the notice of Harrington Brande... (Cronin)

An adverbial modifier expressed by the Nominative Absolute Par­ticipial Construction or any other absolute construction is generally detached.

The train coming in a minute later, the two brothers parted and entered their respective compartments. (Galsworthy)

With his face buried in his hands, he did not see her enter the room. (Keating)

Of all the kinds of adverbial modifiers that of attendant circum­stances is most apt to become detached.

They drove on, without speaking again, to Stanhope Gate. (Galsworthy)

He came in, with a large parcel under his arm. (Collins)

She had moved through its gaudiness and pettiness and glamour, her head high and her lashes low, clothed in an immaculate dignity. (Sanborn)

Nicholas lay there, his brow still contracted, filled with perplexity and confusion. (Cronin)

The kitchen became the sitting room, she and Robert eating their meals before the warm stove. (Lawrence)