Transient radio emission from the PSR B1259-63
system near periastron
S. Johnston (RCfTA, University of Sydney, Australia),
R. N. Manchester (ATNF, CSIRO, Australia),
D. McConnell (ATNF, CSIRO, Australia),
D. Campbell-Wilson (Astrophysics Dept, University of Sydney, Australia),
Abstract
Observations of the pulsar - Be-star binary system PSR B1259-63 around
the 1994 and 1997 periastron encounters, using the Australia Telescope
Compact Array at four frequencies between 1.4 and 8.4 GHz, and the Molonglo
Observatory Synthesis Telescope at 843 MHz, show a relatively strong and
rapidly varying but unpulsed radio source. The source appears 22 d
before periastron and lasts for more than 100 d. Over most of the
event the spectral index is ~ -0.5, indicating an optically thin
synchrotron source. The peak flux of ~50 mJy at 1 GHz occurs about 20 d
after periastron. There are strong similarities in the light curves of
the 1994 and 1997 periastron passages. The radio light curve shows
day-to-day variability and varies by a factor of more than 100 over the
observation interval. This is in contrast to the X-ray emission which varies
by only a factor of two close to periastron. The emission is interpreted as
synchrotron emission from relativistic electrons accelerated in shocks at
the interface between the pulsar wind and the Be-star emission-line disc.