A woman was found dead in a Lowell residence early Sunday morning, authorities said. Police found Elaine Sweeney, 52, of Lowell deadinside a Sparks Street residence at about 2 a.m., the Middlesex district attorney’s office said. Investigators are awaiting the results of a toxicology report to determine how Sweeney died, District Attorney Marian T. Ryan’s office said Sunday. Prosecutors did not say if foul play is suspected. No further information was available Sunday night.