Public Seminar of PhD Candidate:- High-Resolution Radio Study of the Pulsar Wind Nebula MSH 15-52
Pulsar winds are charged particles accelerated by the extremely strong magnetic field of rotation-powered pulsars. When these particles interact with the ambient circumstellar or interstellar material (ISM) around the pulsar, they emit broadband synchrotron radiation. The interacting region formed a nebula which is collectively known as a pulsar wind nebula (PWN). A PWN could be formed by a young pulsar within a supernova remnant (SNR) or by a fast-moving pulsar which gives a bow shock nebula. Synchrotron radiation is the major emission mechanism of PWNe, which is in the range from radio to X-rays. In gamma-rays, the emission mechanism is inverse-Compton scattering of low-energy ambient photons. Young PWNe inside SNRs are often complex and features-rich astronomical objects, their morphology based on the evolution stage of the SNR.
The speaker presents a high-resolution radio imaging study of the PWN MSH 15-52 with new Australia Telescope Compact Array observations at 6 cm and 3 cm. The system is powered by a young and energetic radio pulsar B1509-58 with a high-spin down luminosity of E-dot ~2x10^37 erg per second. Previous X-ray studies found a complex morphology for the PWN. The overall shape resembles a hand, extending over 10 pc with features like a bright collimated jet, double arcs, filaments and enhanced emission knots in the associated H-II region RCW 89.
Unlike the X-ray emission which shows the most recent conditions of PWNe, radio emission has a much longer synchrotron loss timescale. This reflects the integrated history of the injected particles to the system. The new radio images discovered the long-sought radio PWN and show different morphology than the X-ray counterpart. No radio emission is detected at the X-ray jet position, instead an enhanced emission in a shape of sheath surrounds the jet which consists of a bright arc and polarised filaments. Polarisation measurements show that the intrinsic orientation of the magnetic field aligns with the X-ray jet elongation. Small-scale features include a narrow polarised filament across the pulsar, network of filaments and knots in RCW 89. Counterparts of X-ray features like the inner arc, the “thumb” are also discovered. The 6km correlation data were used to measure the position of B1509. The proper motion result could imply the pulsar is moving in the X-ray jet outflow direction.
講者：Wai Yan LEUNG(香港大學 博士生候選人)