2008ApJ...683L.159V

The Guitar Nebula is an Hα nebula produced by the interaction of the relativistic wind of a very fast pulsar, PSR B2224+65, with the interstellar medium. It consists of a ram-pressure confined bow shock near its head and a series of semicircular bubbles further behind, the two largest of which form the body of the Guitar. We present a scenario in which this peculiar morphology is due to instabilities in the backflow from the pulsar bow shock. From simulations, these backflows appear similar to jets and their kinetic energy is a large fraction of the total energy in the pulsar's relativistic wind. We suggest that, like jets, these flows become unstable some distance downstream, leading to rapid dissipation of the kinetic energy into heat, and the formation of an expanding bubble. We show that in this scenario the sizes, velocities, and surface brightnesses of the bubbles depend mostly on observables, and that they match roughly what is seen for the Guitar. Similar instabilities may account for features seen in other bow shocks.