Infrared photometry and polarimetry of Cygnus X-3

Terry Jay Jones, Robert D. Gehrz, Henry A. Kobulnicky, Lawrence A. Molnar, Eric M. Howard

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We present photometry and linear polarimetry of Cygnus X-3 at K (2.2 μm) obtained over a 5 yr period. Photometry and polarimetry at J, H, and K of nearby field stars is also presented. From an analysis of these data we find: (1) Using the x-ray ephemeris of Kitamoto et al. [ApJ, 384, 263 (1992)], including the first and second derivatives of the period, the leading edge of the decline to minimum in the quiescent K light curve has not changed in phase since 1974. The duration of the minimum in the light curve has changed signicantly between different epochs, becoming much broader in 1993 than it was previously. (2) In addition to an interstellar polarization component, it is likely Cyg X-3 has an intrinsic polarization component that is variable. The variations in the polarization do not show any diagnostic pattern with, orbital phase. A crude analysis of the polarization suggests the intrinsic polarization of Cyg X-3 has a mean position angle of ∼12°, nearly the same as the direction of the expanding radio lobes. This is consistent with circumstellar electrons scattering in an equatorial disk that is perpendicular to the lobe axis. (3) The mean position angle for the interstellar polarization in the direction of Cyg X-3 is 150°. This is nearly perpendicular to the axis of interstellar radio scattering seen in the extended VLBI images. Since the position angle of interstellar polarization is the same as the projected magnetic field direction, this suggests the interstellar (not circumstellar) scattering must be taking place perpendicular to the interstellar magnetic field lines. (4) Cyg X-3 was observed at K during a flare on 1992 September 30 with a temporal resolution of 6 s. The flaring had rise and fall times of ∼50 s with peak intensities up to 80 mJy. The flux between individual flare events never dropped to quiescent levels for the duration of our observations (∼2000 s).

Original languageEnglish (US)
Pages (from-to)605-611
Number of pages7
JournalAstronomical Journal
Issue number2
StatePublished - Aug 1994


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