Previous studies have demonstrated that putatively single nitrogen-type Wolf-Rayet stars (WN stars) without known companions are X-ray sources. However, almost all WN star X-ray detections so far have been of earlier WN2-WN6 spectral subtypes. Later WN7-WN9 subtypes (also known as WNL stars) have proved more difficult to detect, an important exception being WR?79a (WN9ha). We present here new X-ray detections of the WNL stars WR?16 (WN8h) and WR?78 (WN7h). These new results, when combined with previous detections, demonstrate that X-ray emission is present in WN stars across the full range of spectral types, including later WNL stars. The two WN8 stars observed to date (WR?16 and WR?40) show unusually low X-ray luminosities (Lx ) compared to other WN stars, and it is noteworthy that they also have the lowest terminal wind speeds (v ∞). Existing X-ray detections of about a dozen WN stars reveal a trend of increasing Lx with wind luminosity Lwind = (1/2)v2∞, suggesting that wind kinetic energy may play a key role in establishing X-ray luminosity levels in WN stars.
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