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We review the observations of supernova remnants (SNRs) and pulsar-windnebulae (PWNe) that give information on the strength and orientation ofmagnetic fields. Radio polarimetry gives the degree of order of magneticfields, and the orientation of the ordered component. Many young shellsupernova remnants show evidence for synchrotron X-ray emission. The spatialanalysis of this emission suggests that magnetic fields are amplified by one totwo orders of magnitude in strong shocks. Detection of several remnants in TeVgamma rays implies a lower limit on the magnetic-field strength (or ameasurement, if the emission process is inverse-Compton upscattering of cosmicmicrowave background photons). Upper limits to GeV emission similarly providelower limits on magnetic-field strengths. In the historical shell remnants,lower limits on B range from 25 to 1000 microGauss. Two remnants showvariability of synchrotron X-ray emission with a timescale of years. If thistimescale is the electron-acceleration or radiative loss timescale, magneticfields of order 1 mG are also implied. In pulsar-wind nebulae, equipartitionarguments and dynamical modeling can be used to infer magnetic-field strengthsanywhere from about 5 microGauss to 1 mG. Polarized fractions are considerablyhigher than in SNRs, ranging to 50 or 60% in some cases; magnetic-fieldgeometries often suggest a toroidal structure around the pulsar, but this isnot universal. Viewing-angle effects undoubtedly play a role. MHD models ofradio emission in shell SNRs show that different orientations of upstreammagnetic field, and different assumptions about electron acceleration, predictdifferent radio morphology. In the remnant of SN 1006, such comparisons imply amagnetic-field orientation connecting the bright limbs, with a non-negligiblegradient of its strength across the remnant.

Magnetic fields in supernova remnants and pulsar-wind nebulae