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X-Ray Polarimetry Workshop SLAC, Stanford, California 9-11 February 2004 |
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New optical polarization measurements of the Crab pulsar
Gottfried
Kanbach
Max-Planck-Inst. f. Extraterrestrische Physik
gok@mpe.mpg.de
G. Kanbach, A. Wozna*, S. Kellner**, H. Steinle (MPE, Garching, Germany) * now at NCAC, Torun, Poland ** now at MPIA, Heidelberg, Germany
We have observed the Crab nebula and pulsar for about 3 hours with the high-speed photo-polarimeter OPTIMA in January 2002 at the Calar Alto 3.5m telescope. The instrumental sensitivity (white light) extends from about 450nm to 950nm and the used polaroid filter modulates the incoming radiation effectively for wavelengths shorter than 850nm. Astronomical targets are imaged onto a hexagonal bundle of optical fibers which are coupled to single photon APD counters. The spacing and size of the fibers corresponds to about 2 arcsec. GPS based time tagging of single photons, together with the instantaneous determination of the orientation of a rotating polaroid filter, allows to measure the phase dependent linear polarization state of the pulsar and the surrounding nebula simultaneously. The Crab pulsar and its net optical polarization are determined at all phases of rotation with high statistical accuracy. We also separated the so-called off-pulse phase emission, with an intensity of about 1.2% compared to the first peak (assumed to be present at all phases), from the pulsed emission and show the 'net' polarization of the pulsed structures. Recent theoretical results indicate that the measured optical polarization of Crab is similar to expectations from a two-pole caustic emission model.
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For more information, contact
Jennifer Formichelli |
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