Abstract
ApJ, Volume 736, Issue 2, article id. 118 (2011) We present a sequence of five deep observations of SS433 made over the summer
of 2007 using the VLA in the A configuration at 5 and 8 GHz. In this paper we
study the brightness profiles of the jets and their time evolution. We also
examine the spectral index distribution in the source. We find (as previously
reported from the analysis of a single earlier image) that the profiles of the
east and west jets are remarkably similar if projection and Doppler beaming are
taken into account. The sequence of five images allows us to disentangle the
evolution of brightness of individual pieces of jet from the variations of jet
power originating at the core. We find that the brightness of each piece of the
jet fades as an exponential function of age (or distance from the core),
exp(-tau/tau'), where tau is the age at emission and tau' = 55.9 +- 1.7 days.
This evolutionary model describes both the east and west jets equally well.
There is also significant variation (by a factor of at least five) in jet power
with birth epoch, with the east and west jets varying in synchrony. The lack of
deceleration between the scale of the optical Balmer line emission (10^15 cm)
and that of the radio emission (10^17 cm) requires that the jet material is
much denser than its surroundings. We find that the density ratio must exceed
300:1.