A weak compact jet in a soft state of Cygnus X-1
Journal article, 2012
We present evidence for the presence of a weak compact jet during a soft X-ray state of Cygnus X-1. Very-high-resolution radio observations were taken with the VLBA, EVN and MERLIN during a hard-to-soft spectral state change, showing the hard state jet to be suppressed by a factor of about 35 in radio flux and unresolved to direct imaging observations (i.e. ?1 mas at 4 cm). High time-resolution X-ray observations with the RXTE-PCA were also taken during the radio monitoring period, showing the source to make the transition from the hard state to a softer state (via an intermediate state), although the source may never have reached the canonical soft state. Using astrometric very long baseline interferometry (VLBI) analysis and removing proper motion, parallax and orbital motion signatures, the residual positions show a scatter of similar to 0.2 mas (at 4 cm) and similar to 3 mas (at 13 cm) along the position angle of the known jet axis; these residuals suggest that there is a weak unresolved outflow, with varying size or opacity, during intermediate and soft X-ray states. Furthermore, no evidence was found for extended knots or shocks forming within the jet during the state transition, suggesting that the change in outflow rate may not be sufficiently high to produce superluminal knots.
ISM: jets and outflows
black-holes
stars: individual: Cygnus X-1
X-rays: binaries
x-ray binaries
efficient
grs 1915+105
radio-emission
gx 339-4
orbital modulation
variability
relativistic jet
vlbi observations
Author
Anthony Rushton
Chalmers, Earth and Space Sciences, Onsala Space Observatory
J. C. A. Miller-Jones
Curtin University
R. Campana
INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Rome
Y. Evangelista
INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Rome
Z. Paragi
Magyar Tudomanyos Akademia
Joint Institute for VLBI in Europe
T. J. Maccarone
University of Southampton
G. G. Pooley
University of Cambridge
V. Tudose
Academia Romana
Netherlands Foundation for Research in Astronomy
Institute of Atomic Physics, Bucharest
R. P. Fender
University of Southampton
R. E. Spencer
University of Manchester
V. Dhawan
National Radio Astronomy Observatory Socorro
Monthly Notices of the Royal Astronomical Society
0035-8711 (ISSN) 1365-2966 (eISSN)
Vol. 419 4 3194-3199Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1111/j.1365-2966.2011.19959.x