Swift X-ray Afterglows and the Missing Jet Break Problem
  We present a systematic survey of the temporal and spectral properties of all GRB X-ray afterglows observed by Swift-XRT between January 2005 and July 2007. We have constructed a catalog of all light curves and spectra and investigate the physical origin of each afterglow segment in the framework of the forward shock models by comparing the data with the closure relations. We search for possible jet-like breaks in the lightcurves and try to explain some of the "missing" X-ray jet breaks in the lightcurves. 
J. L. Racusin (1), E.-W. Liang (2,3), D. N. Burrows (1), D. C. Morris   (1), B. B. Zhang (2), B. Zhang (2) ((1) Pennsylvania...