A weak compact jet in a soft state of Cygnus X-1
Artikel i vetenskaplig tidskrift, 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.

X-rays: binaries

grs 1915+105


gx 339-4


ISM: jets and outflows

relativistic jet

vlbi observations



x-ray binaries

orbital modulation

stars: individual: Cygnus X-1


Anthony Rushton

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

J. C. A. Miller-Jones

Curtin University

R. Campana

Istituto nazionale di astrofisica (INAF)

Y. Evangelista

Istituto nazionale di astrofisica (INAF)

Z. Paragi

Joint Institute for VLBI in Europe (JIVE)

Magyar Tudomanyos Akademia

T. J. Maccarone

University of Southampton

G. G. Pooley

University of Cambridge

V. Tudose

Netherlands Institute for Radio Astronomy (ASTRON)

Academia Romana

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 3194-3199


Astronomi, astrofysik och kosmologi



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