Magnetic Field Structure around the Crab Pulsar

Abstract

LINEAR polarization observations of the Crab nebula at optical wavelengths indicate that the magnetic field is uniform in direction over a large region (about 0.5 pc) around the pulsar. Observations were made with a completely automatic sky compensated polarimeter-cum-photometer with an S20 photomultiplier and a GG13 filter. A ‘Fabri-Tek’ computer in the pulse counting mode was used to store data for each degree of rotation of the Polaroid filter during each observation and a digital magnetic tape recorder was used for permanent data storage. A ‘CDC 6400’ computer was then used for direct reduction of the magnetic tapes. A complete description of the instrument and data system will be given in a later publication. Observations were made on November 4 and 5, 1969, and on February 1 and 2, 1970, with the 84 inch telescope at Kitt Peak. Three standard stars, HI 29, HDE 253683 and HDE 251204 (ref. 1), were used to calibrate the observations and an unpolarized star was used to evaluate the instrumental polarization. All angles reported in this paper are measured from north towards east.