4065 10 archive 337 disk0/00/00/40/65 2008-04-07 14:20:47 2008-09-01 23:09:14 2008-07-16 17:04:48 article show john.dickey@utas.edu.au Phillips CJ Dickey JM john.dickey@utas.edu.au Fender RP Tudose V Nicolson GD Deller A Amy SW Tingay SJ Tzioumis AK Reynolds JE Jauncey DL Stevens JB Jamie.Stevens@utas.edu.au Ellingsen S Simon.Ellingsen@utas.edu.au pub 240101 970102 780102 restricted instrumentation: interferometers • techniques: interferometric • radio continuum: stars • X-rays: stars • X-rays: individual: Circinus X The definitive version is available at www.blackwell-synergy.com category => A1 categoryDesc => Refereed Article in a Scholarly Journal eprintID => 0 field1 => Monthly Notices of the Royal Astronomical Society field10 => field11 => field12 => field13 => field2 => "Oxford, England" field3 => 380 field4 => 1 field5 => L11-L14 field6 => Blackwell Publishing field7 => 0035-8711 field8 => field9 => funding => Q grant => E0014809 lastUpdate => 29/08/2007 rfcd => 240101 seo => 780102 themeArea => FT title => Detection of compact radio emission from Circinus X-1 with the first Southern hemisphere e-VLBI experiment tor => PB uid => 46691 update => no Circinus X-1 has recently returned to a state of strong radio flaring. Here we report on the first VLBI observations, and detection, undertaken in the 25 years since the 1975–1985 period of strong recurrent flaring activity.We detected Circinus X-1 with the first observations conducted by a recently developed Southern hemisphere e-VLBI array, at both 1.6 and 8.4 GHz, over a three-day period. At 1.6 GHz, the compact source has a total flux density of 11 mJy and a size of 60 ± 15 mas (Gaussian model full width at half maximum). At 8.4 GHz, the compact source is less than 60 mas. The size variation with frequency is consistent with a broadened image due to scattering in the turbulent, ionized interstellar medium of our Galaxy. However, these size measurements appear inconsistent with the λ2.2 variation expected for strong interstellar scattering and previous VLBI observations made at 2.3 GHz in the early 1980s. To explain this apparent inconsistency, we suggest that Circinus X-1 supports a weak, non-varying component of 35 mas extent (175 au at 5 kpc distance), corresponding to compact structure in the extended radio nebula. No significant variation in the flux density at 1.6 GHz is evident between two observations 24 h apart. No jet-like structures are evident on scales of tens of mas, simply a scatter broadened source, presumably coincident with the suggested neutron star in the binary system. 2007 published Monthly Notices of the Royal Astronomical Society 380 1 Blackwell Publishing L11-L14 10.1111/j.1745-3933.2007.00339.x TRUE 0035-8711 http://dx.doi.org/10.1111/j.1745-3933.2007.00339.x 6498 3 4065 1 application/pdf en staffonly

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