  The main objective of the FROST experiment at Jefferson Lab is the study of
baryon resonances. The polarization observable E for the reaction gamma p to
pi+n has been measured as part of this program. A circularly polarized tagged
photon beam with energies from 0.35 to 2.35 GeV was incident on a
longitudinally polarized frozen-spin butanol target. The final-state pions were
detected with the CEBAF Large Acceptance Spectrometer. Preliminary polarization
data agree fairly well with present SAID and MAID partial-wave analyses at low
photon energies. In most of the covered energy range, however, significant
deviations are observed. These discrepancies underline the crucial importance
of polarization observables to further constrain these analyses.
