Speaker
Description
A peculiar spectral pattern, resembling "zebra stripes", of the Crab pulsar's high-frequency interulse (HFIP) radio emission has remained puzzling for two decades, since its first detection in 2007. This pattern, observed in pulsar's dynamic spectra between 5 GHz and 30 GHz, exhibits exceptional stability, nearly 100% polarization, and a distinctive excess Dispersion Measure. Very recently, a comprehensive theory explaining the phenomenon and accounting for all the observed peculiarities has been developed. The observed spectral emission bands are shown to be interference maxima caused by multiple ray propagation through the pulsar inner magnetosphere. The high-contrast interference pattern is the combined effect of gravitational lensing and plasma de-lensing of light rays. Remarkably, the model enables space-resolved tomography of the pulsar magnetosphere with unprecedented resolution of 30 nanoarcseconds (corresponding to the scale of ~100 km observed from the distance of 2 kpc). The model yields a plasma density profile of n_e~1/r^3, which perfectly agrees with theoretical insights. Further, we predict the zebra pattern trend to change at a higher frequency when the ray separation becomes smaller than the neutron star size. This frequency is predicted to be in the range between 42 GHz and 650 GHz, which is within the reach of existing facilities like ALMA and SMA. These observations hold significant importance and would contribute to our understanding of the magnetosphere. Furthermore, they offer the potential to investigate gravity in the strong field regime near the star's surface.
