The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNS13025702
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Of Total Unemployed, Percent Unemployed 15 to 26 Weeks [LNS13025702], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/LNS13025702/, September 3, 2015.
FRED BlogTracking the duration of unemployment