Insights from cosmic-ray positron measurements about young pulsar gravitational and electromagnetic energy losses

Young gamma-ray pulsars are thought to be efficient accelerators of electrons. However, they have also been proposed as sources of gravitational waves. Estimates of the pulsar birthrate (PB) and cosmic-ray positron measurements above a few GeV allow us to set an upper limit to the average energy loss of young pulsars in our galaxy due to gravitational wave emission. This occurs when a model of positron production at the pulsar polar cap is assumed. The upper limit is found to lie well above those obtained through the observed braking indexes (n) from young pulsars such as Crab or Vela. This result might indicate additional electromagnetic energy losses such as photon production at the outer gap in the pulsar magnetosphere. Pulsed gamma-ray observations above a few GeV from a large sample of young pulsars and small-error cosmic-ray positron measurements will clarify the role of polar cap and outer gap models in the near future. A fundamental cross-check will be allowed by Earth interferometers for gravitational wave detection from radio pulsars.