Title: Weak Lensing Flexion and Plasma Lensing

Speaker: Professor Xinzhong Er (Tianjin Normal University )

Time: 10:00am, Ocober 16, 2024

Location: 3-302, PMO Xianlin Campus

Abstract: In weak lensing we measure the shape distortions of the background galaxies. When the gravitational fields become strong, the image will be distorted beyond the shear, and forms arclet. We call such higher order image distortions ‘flexion’. Flexion is sensitive to the asymmetric mass distribution of the lens, and can be used to probe the small scale structures. But the measurement of flexion is difficult and we hope to achieve that from the images taken by the space-borne telescopes.

In the other work, I would like to introduce the ‘plasma lensing’. Besides gravity, the ionized plasma in the universe can deflect the propagation of the light as well. Unlike the gravitational lensing, the plasma lensing has frequency dependence, and only becomes significant at radio bands. Thus the typical sources of the plasma lensing are QSO, pulsars, FRBs, all of which are point-like sources. Thus the magnification and time delay effects are the two interesting properties in plasma lensing. We can see that it will change the dispersion relation and Faraday rotation relation.