Pulsar wind nebulae around the southern pulsars PSR B1643-43 and PSR B1706-44

We present high-resolution VLA images taken at the wavelengths of 20, 6, an d 3.6 cm in the vicinity of the pulsars PSR B1706-44 (PSR J1709-4428) and P SR B1643-43 (PSR J1646-4346). Both of these pulsars are young (<30,000 yr) and have large spin-down luminosities ((E)over dot > 10(35) ergs s(-1)) and hence are good candidates to search for extended synchrotron nebulae excit ed by the relativistic pulsar wind. For PSR B1643-43 we found evidence of a 4' comet-shaped nebula, suggestive of a synchrotron "wake" left by a fast- moving pulsar. PSR B1706-44 appears surrounded by a spherical nebula approx imately 3' in diameter. Based on their morphology, the detection of signifi cant linear polarization (>20%), and their flat radio spectra (alpha =0.25- 0.3, where S-nu proportional to nu (-alpha)), we argue that these are wind nebulae powered by the rotational energy loss of the respective pulsars.