Kavli Affiliate: Kejia Lee
| First 5 Authors: Shunshun Cao, Jinchen Jiang, Jaroslaw Dyks, Kejia Lee, Jiguang Lu
| Summary:
We analyze and model rapid rotations of polarization orientations in PSR
B1919+21’s single pulses based on Five-hundred-meter Aperture Spherical radio
Telescope observation data. In more than one-third of B1919+21’s single pulses,
the polarization position angle (PA) is found to rotate quasi-monotonically
with pulse longitude, by over 180 degrees or even 360 degrees. Some single
pulse PA even rotates by over 540 degrees. Most of these quasi-monotonic PA
curves have negative slopes with respect to pulse longitude. Oscillations of
circular polarization fraction accompany these PA rotations. This rapid
rotation could be induced by a quick change of phase lag between two normal
wave modes within an individual pulse. We propose a phenomenological model to
reproduce the observed polarization rotations in single pulses, and calculate
phase lags in a dipolar magnetic field of an aligned rotating pulsar, with a
dispersion relation of orthogonal wave modes in strongly magnetized
electron-positron plasma. According to the dispersion relation, the weak
frequency dependence of observed polarization rotation requires small angles
between the radio wavevector and local magnetic fields, which requires the
radio emission height to be low, on the order of 10 times neutron star radius.
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