An unusual pulsar wind nebula associated with PSR B0906-49
B. M. Gaensler (Astrophysics Dept, University of Sydney, Australia),
B. W. Stappers (MSSSO, ANU, Australia),
D. A. Frail (NRAO, Socorro, USA),
S. Johnston (RCfTA, University of Sydney, Australia),
Abstract
We report on Australia Telescope Compact Array observations of the
~10^5 yr old pulsar PSR B0906-49. In an image containing only
off-pulse emission, we find a weak, slightly extended source coincident
with the pulsar's position, which we argue is best interpreted as a
pulsar wind nebula (PWN). A trail of emission extending behind the
pulsar aligns with the major axis of the PWN, and implies that
the pulsar is moving north-west with projected velocity
~60 kms, consistent with its scintillation speed. The
consequent density we infer for the pulsar's environment is
>2 cm^-3, so that the PWN around PSR B0906-49 is confined mainly
by the high density of its surroundings rather than by the pulsar's
velocity. Other properties of the system such as the PWN's low
luminosity and apparent steep spectrum, and the pulsar's large
characteristic age, lead
us to suggest that this nebula is substantially different from other
radio PWNe, and may represent a transition between young pulsars with
prominent radio PWNe and older pulsars for which no radio PWN has been
detected. We recommend that further searches for radio PWNe should be
made as here: at low frequencies and with the pulsed emission subtracted.