Identification of the nebula G70.7 + 1.2 as a bow shock powered by a pulsar/Be-star binary

Abstract

The enigmatic radio and optical nebula G70.7 + 1.2 has been suggested to be a young supernova remnant a nova shell, a cometary H II region and a protostellar outflow. Claims of strong nonthermal radio emission cast severe doubts on all but the supernova remnant model, but for this the expansion velocity would be low. We present here new data that firmly establish the nonthermal nature of the radio emission, and from Hα and [O I] Fabry–Perot observations we argue that the extended optical emission arises from a bow shock powered by a mass-losing luminous (Be) star moving supersonically through dense gas. The nonthermal emission is then explained as the shocked relativistic wind from a pulsar, which we propose is a companion to the Be star. The coincidence of the optical and radio emission requires the pulsar and stellar winds to be mixed together. The system has a large overall velocity, ~60 km s^(−1), which is inexplicable in all other models but which is typical of binary pulsars. Detection of pulsed emission and of the predicted proper motion would confirm our proposal.