Long-term radio behaviour of the X-ray binary circinus X-1
Proceedings of Science 56 (2007)
Abstract:
Circinus X-1 is a neutron star X-ray binary system with an interesting and at times puzzling behaviour over a broad range of frequencies, specifically in the X-ray and radio bands. The system seems to harbour the most relativistic outflow (likely oriented close to the line of sight) observed so far within the Milky Way. It lies within a radio synchrotron nebula and has variable radio flux densities at cm wavelengths. The radio flares associated to the orbital phase zero reached up to 1 Jy in the late '70s, then have been observed at the tens of mJy level until recently; in 2007 January, Circinus X-1 seemed to have entered a very active radio flaring state. Here we present a sample of the 4.8 and 8.6 GHz radio observations made with the Australia Telescope Compact Array, covering 10 years time period. The entire data set comprised 41 epochs, unequally spread in time between 1996 and 2006. We investigate the long-term changes in the brightness, morphology and spectrum of the radio structures. We have detected linear polarisation in a third of the epochs and a good case for Faraday rotation in one epoch. The analysis reveals structural changes in the radio emission at time scales as short as days. Clear evidence for a counter-jet was found in a few epochs.Predicting radio activity in X-ray binaries with optical/infrared monitoring
Proceedings of Science 56 (2007)
Abstract:
X-ray binaries undergo outbursts due to increased mass accretion rate in the disc towards the compact object, a black hole or neutron star. Recently, a picture has developed where the behaviour between the radio, optical/infrared and X-ray luminosities during these outbursts are correlated. Here, I review this picture and show how simple optical/infrared monitoring can predict radio flux densities. Using these predictions it will be possible to prepare radio telescopes accordingly, eventually improving radio sampling of X-ray transients. In particular, it is possible to infer when the bright, optically thin jet flares are likely to occur in black hole transients. We find that the hard-to-soft X-ray state changes, which also can be identified by optical/infrared colour changes, lead the bright optically thin radio outbursts by ∼ 10 days.Simultaneous X-ray/radio observations of Cir X-1
Proceedings of Science 56 (2007)
Abstract:
We analysed simultaneous X-ray/radio observations of Circinus X-1 collected respectively with RXTE and ATCA in 2000 October and 2002 December and identified radio flares close to phase 0.0 and 0.5 of the orbital period. To date, there is only circumstantial evidence for radio flares near phase 0.5. Moreover, in our data set, we clearly associated both a radio flare and X-ray spectral timing changes with phase 0.0. While for black hole X-ray binaries the picture of the association between the X-ray and the radio bands is quite well understood, for neutron star X-ray binaries a clear and complete picture is still missing.THREE-DIMENSIONAL BAR STRUCTURE AND DISC/BULGE SECULAR EVOLUTION
Springer Nature (2007) 181-186
The SAURON project - XI. Stellar populations from absorption-line strength maps of 24 early-type spirals
Monthly Notices of the Royal Astronomical Society 379:2 (2007) 445-468