Non-thermal X-ray and Radio Emission from the Snr N 157b

The supernova remnant N 157B contains a pulsar and three distinct synchrotron components with rather unusual properties. 1) A somewhat irregular elliptical pulsar wind nebula (PWN) visible in both X-ray and radio wavelengths. The nebula is quite symmetrical with an extent of about 10 × 5 parsecs but offset along the long axis by about 4 pc from the pulsar position. It is apparently the result of a short-lived injection of energetic particles, perhaps starting at the time of explosion. 2) A very bright X-ray shock region located just outside the pulsar position in the edge of the PWN. This is undetected in the radio. We attribute this to a new burst of particles from the pulsar suggesting there are multiple episodes rather than continuous injection. 3) The beginning of a radio synchrotron shell on the southern side of the SNR where thermal X-rays appear to arise suggesting that N 157B is starting to become a composite SNR.