Professor Marten van Kerkwijk

Pulsars scintillate because their radiation is slightly bent by material along the line of sight, causing multiple images that interfere with each other. The speaker will discuss how this might be used for very high resolution astrometry. He will describe observations of one particular pulsar, PSR B1957+20, the original black widow pulsar. These were taken to try to resolve the orbit astrometrically, something we have not yet succeeded in doing, but also led to several serendipitous discoveries, of mode changes and giant pulses (and correlations between those), and, most spectacularly, of great variations in pulsar flux near pulsar eclipse (by material surrounding its companion). Some of latter excursions exceed an order of magnitude over our 48 MHz band. The higher magnification events are strongly chromatic, with magnifications reaching over two orders of magnitude in small frequency bands. The speaker will show that in the high-magnification events, the pulsar magnetosphere is resolved, allowing one to estimate the physical sizes of and separation between the emission regions responsible for the main- and inter-pulse. He will also discuss the puzzling lack of evidence for any magnetic field in the lensing plasma.