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Session 57 - Astrophysical Diagnostics from Polarimetry.
Display session, Wednesday, June 12
Tripp Commons,
The High Speed Photometer (HSP) on the Hubble Space Telescope observed SS433 at 16 different epochs between 1993 May and November. Polarimetric observations were obtained in a 340 ÅFWHM bandpass centered at 2770 Åphotometric observations were made in a bandpass extending between 1400 and 3000 ÅThe magnitude of the polarization in the UV is variable, reaching a maximum p >20%, a value as large as that observed in the radio, and unexpectedly larger than that observed in the visible. The mean position angle of the polarization in the UV is 90\deg, again similar to the position angle of the polarization observed in the radio and orthogonal to the 0\degposition angle observed in the visible. The position angle in the UV varies in phase with the 164 d period in a way similar to that observed in the radio. The polarized radiation we observe in the UV must be emitted from the precessing relativistic jets that ultimately produce the polarized radio emission rather than the scattering region producing the optical polarization. Gyro-synchrotron emission from the material moving at semi-relativistic velocity in the jets is a mechanism which can produce UV radiation with properties consistent with all the observations. SS433 would then be the first astronomical source known to emit gyro-synchrotron radiation at non-radio frequencies. Less than 1.2% of the flux from SS433 between 1400 and 3000 Åis pulsed with a period between 200 \mus and 100 s at 164 d phase \psi = 0.131, when the spectral line systems have their smaller maximal separation in radial velocity.
