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Register a new userThe large-scale jet-powered radio nebula of Circinus X-1
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We present multi-epoch observations of the radio nebula around the neutron star X-ray binary Circinus X-1 made at 1.4 and 2.5 GHz with the Australia Telescope Compact Array between October 2000 and September 2004. The nebula can be seen as a result of the interaction between the jet from the system and the interstellar medium and it is likely that we are actually looking toward the central X-ray binary system through the jet-powered radio lobe. The study of the nebula thus offers a unique opportunity to estimate for the first time using calorimetry the energetics of a jet from an object clearly identified as a neutron star. An extensive discussion on the energetics of the complex is presented: a first approach is based on the minimum energy estimation, while a second one employs a self-similar model of the interaction between the jets and the surrounding medium. The results suggest an age for the nebula of leq 10^5 years and a corresponding time-averaged jet power geq 10^{35} erg s^{-1}. During periodic flaring episodes, the instantaneous jet power may reach values of similar magnitude to the X-ray luminosity.
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We present H-alpha and [O III] (5007 Angstroms) images of the nebula powered by the jet of the black hole candidate and microquasar Cygnus X-1, observed with the 2.5m Isaac Newton Telescope (INT). The ring-like structure is luminous in [O III] and there exists a thin outer shell with a high [O III] / H-alpha flux ratio. This outer shell probably originates in the collisionally excited atoms close to the front of the bow shock. Its presence indicates that the gas is shock excited as opposed to photoionised, supporting the jet-powered scenario. The shock velocity was previously constrained at 20 < v < 360 km/s; here we show that v >= 100 km/s (1 sigma confidence) based on a comparison of the observed [O III] / H-alpha ratio in the bow shock with a number of radiative shock models. From this we further constrain the time-averaged power of the jet: P_Jet = (4 - 14)*10^36 erg/s. The H-alpha flux behind the shock front is typically 4*10^-15 erg/s/cm^2/arcsec^2, and we estimate an upper limit of ~8*10^-15 erg/s/cm^2/arcsec^2 (3 sigma) to the optical (R-band) continuum flux of the nebula. The inferred age of the structure is similar to the time Cyg X-1 has been close to a bright H II region (due to the proper motion of the binary), indicating a dense local medium is required to form the shock wave. In addition, we search a > 1 square degree field of view to the south of Cyg X-1 in H-alpha (provided by the INT Photometric H-alpha Survey of the Northern Galactic Plane; IPHAS) for evidence of the counter jet interacting with the surrounding medium. Two candidate regions are identified, whose possible association with the jet could be confirmed with follow-up observations in [S II] and deeper observations in [O III] and radio.
We analyzed the zero-order image of a 50 ks Chandra gratings observation of Circinus X-1, taken in 2005 during the sources low-flux state. Circinus X-1 is an accreting neutron star that exhibits ultra-relativistic arcsecond-scale radio jets and diffuse arcminute-scale radio jets and lobes. The image shows a clear excess along the general direction of the north-western counter-jet, coincident with the radio emission, suggesting that it originates either in the jet itself or in the shock the jet is driving into its environment. This makes Circinus X-1 the first neutron star for which an extended X-ray jet has been detected. The kinetic jet power we infer is significantly larger than the minimum power required for the jet to inflate the large scale radio nebula.
We present results from the first successful millimetre (combined 33 GHz and 35 GHz) observations of the neutron star X-ray binary Circinus X-1, using the Australia Telescope Compact Array. The source was clearly detected in all three observing epochs. We see strong evidence for a periastron flare beginning at MJD 55519.9 pm 0.04 with estimated peak flux densities of up to 50 mJy and which proceeds to decline over the following four days. We directly resolve jet structures on sub-arcsecond scales. Flux density variability and distance from the core of nearby components suggests recent shock re-energisation, though we are unable to directly connect this with the observed flare. We suggest that, if the emission is powered by an unseen outflow, then a phase delay exists between flare onset and subsequent brightening of nearby components, with flows reaching mildly relativistic velocities. Given resolved structure positions, in comparison to past observations of Cir X-1, we find evidence that jet direction may vary with distance from the core, or the sources precession parameters have changed.
We present the first resolved imaging of the milliarcsecond-scale jets in the neutron star X-ray binary Circinus X-1, made using the Australian Long Baseline Array. The angular extent of the resolved jets is ~20 milliarcseconds, corresponding to a physical scale of ~150 au at the assumed distance of 7.8 kpc. The jet position angle is relatively consistent with previous arcsecond-scale imaging with the Australia Telescope Compact Array. The radio emission is symmetric about the peak, and is unresolved along the minor axis, constraining the opening angle to be less than 20 degrees. We observe evidence for outward motion of the components between the two halves of the observation. Constraints on the proper motion of the radio-emitting components suggest that they are only mildly relativistic, although we cannot definitively rule out the presence of the unseen, ultra-relativistic (Lorentz factor >15) flow previously inferred to exist in this system.
We present the results of millimetre (33 and 35 GHz) and centimetre (2.1, 5.5 and 9.0 GHz) wavelength observations of the neutron star X-ray binary Circinus X-1, using the Australia Telescope Compact Array. We have used advanced calibration and deconvolution algorithms to overcome multiple issues due to intrinsic variability of the source and direction dependent effects. The resulting centimetre and millimetre radio maps show spatially resolved jet structures from sub-arcsecond to arcminute angular scales. They represent the most detailed investigation to date of the interaction of the relativistic jet from the X-ray binary with the young supernova remnant in which it is embedded. Comparison of projected jet axes at different wavelengths indicate significant rotation of the jet axis with increasing angular scale. This either suggests interactions of the jet material with surrounding media, creating bends in the jet flow path, or jet precession. We explore the latter hypothesis by successfully modelling the observed jet path using a kinematic jet model. If precession is the right interpretation and our modelling correct, the best fit parameters describe an accreting source with mildly relativistic ejecta ($v = 0.5 c$), inclined close to the plane of the sky ($i = 86^{circ}$) and precessing over a 5-year period.
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