High-resolution radio study of the pulsar wind nebula MSH 15-52

Abstract

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.

We present 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 ~ 2 x 10^37 erg/s. 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 HII 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.