Pulsar-powered nebulae:

The Crab Nebula was the first detected source of VHE gamma-rays ([Weekes et al. 1989]) and remains the standard candle for VHE observations. Unpulsed VHE emission from PSR1706-44 ([Kifune et al. 1995]; [Chadwick et al. 1998]) and Vela ([Yoshikoshi et al. 1997]) suggest that plerions like the Crab Nebula may be the most prominent members of a large galactic source population. A crucial step to understanding the production mechanism of gamma-rays from plerions is to determine accurately the spectrum of the VHE gamma-rays. Because VHE gamma-rays are at or near the end of the electromagnetic spectrum, their measurement provides some of the strongest constraints on the models. When combined with observations of the synchrotron emission spectrum, the VHE measurements can also be used to derive the nebular magnetic field. Whipple observations have now produced an accurate estimate of this spectrum for the Crab Nebula which is consistent with synchrotron-inverse Compton emission (Figure 7; [Hillas et al. 1998]).

  

Figure 7: Crab spectrum from EGRET and VHE observations showing inverse Compton model fits for various values of the nebular magnetic field. Figure from Hillas et al. (1998).

With its improved sensitivity, VERITAS should be able to detect Crab-like objects anywhere within the Galaxy if their declination is $>-28^\circ$. Its improved energy resolution and broader energy coverage will significantly improve spectral measurements leading to more accurate estimates of the nebular magnetic field and maximum electron energy and more detailed tests of gamma-ray emission models. The excellent angular resolution of VERITAS may even make it possible to resolve the VHE emission region of nearby objects like the Crab Nebula.