Optical Polarimetry of the Crab Nebula

Time-resolved polarisation measurements of pulsars provide an unique insight into the geometry of the emission regions. Hubble Space Telescope (HST) polarisation data of the Crab Nebula were obtained from the Multimission Archive at STScI (MAST). The data are composed of a series of observations of the Crab Nebula with the HST and ACS camera system taken in three different polarisation filters (0°, 60° and 120°) between 2003 August and 2005 December. Polarisation vector maps of the Nebula were produced with the polarimetry software IMPOL. The degree of polarisation (P.D.) and the position angle (P.A.) of the pulsar's integrated pulse beam were measured, and also that of the nearby Synchrotron Knot, yielding P.D. = 4.90 +/- 0.33 %, P.A. = 106°.46 +/- 1°.9 for the pulsar, and P.D. = 61.70 +/- 0.72 %, P.A. = 126°.86 +/- 0°.23 for the Synchrotron Knot. These results are consistent with those of obtained by others using INTEGRAL.