Rapid Rotation of Polarization Orientations in PSR B1919+21’s Single Pulses: Implications On Pulsar’s Magnetospheric Dynamics

Kavli Affiliate: Kejia Lee

| First 5 Authors: Shunshun Cao, Jinchen Jiang, Jaroslaw Dyks, Kejia Lee, Jiguang Lu

| Summary:

We analyse and model rapid rotations of polarization orientations in PSR
B1919+21’s single pulses, based on FAST observation data. In more than one
third of B1919+21’s single pulses, polarization angle (PA) is found to rotate
quasi-monotonically with pulse longitude, by over 180 or even 360 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 quick change of phase lag
between normal wave modes within an individual pulse. We propose a
phenomenological model to successfully 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 plasma. The weak frequency dependence of
observed polarization rotation requires the radio emission height to be low,
approximately 10 times the neutron star radius.

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