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[8.07] Who Turned off the lights: Evidence of a Power-loss Threshold for Generating a Bright Pulsar Wind Nebula.

E.V. Gotthelf (Columbia University)

We report further results from an ongoing spectroscopic X-ray survey of energetic rotation-powered pulsars using data obtained with the Chandra X-ray observatory. It is shown that all measured pulsars with \dot E > \dot E_c \approx 4 \times\ 10³⁶ erg s^-1 are X-ray bright, manifest a distinct pulsar wind nebula (PWN), and are associated with a supernova event, either historically or via a thermal remnant. Over half these systems reside in shell-like supernova remnants. Below \dot E_c, the 2-10 keV PWN flux ratio F_PWN/F_PSR is found to decreases by an order-of-magnitude. This result is consistent with the lack of detected radio PWN for pulsar with measure spin-down power below the X-ray derived threshold. An \dot E threshold is also consistent with a lower bound on the 2-10 keV spectral index \Gamma_min = 0.5 observed for rotation-powered pulsars (Gotthelf 2003). The apparent lack of bright pulsar nebulae below a critical \dot E_c suggests a change in the particle injection spectrum and serves as a constraint on emission models for rotation-powered pulsars. This results implies that neither a young age nor a high density environment is found to be a sufficient condition for generating a PWN.

This work is made possible by NASA LTSA grant NAG 5-7935.

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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.