Detection of compact radio emission from Circinus X-1 with the first Southern hemisphere e-VLBI experiment

  1. C. J. Phillips1,*,
  2. A. Deller2,
  3. S. W. Amy1,
  4. S. J. Tingay2,
  5. A. K. Tzioumis1,
  6. J. E. Reynolds1,
  7. D. L. Jauncey1,
  8. J. Stevens3,
  9. S. P. Ellingsen3,
  10. J. Dickey3,
  11. R. P. Fender4,
  12. V. Tudose5,6,
  13. G. D. Nicolson7

Article first published online: 6 JUL 2007

DOI: 10.1111/j.1745-3933.2007.00339.x

Issue

Monthly Notices of the Royal Astronomical Society: Letters

Monthly Notices of the Royal Astronomical Society: Letters

Volume 380, Issue 1, pages L11–L14, September 2007

Additional Information

How to Cite

Phillips, C. J., Deller, A., Amy, S. W., Tingay, S. J., Tzioumis, A. K., Reynolds, J. E., Jauncey, D. L., Stevens, J., Ellingsen, S. P., Dickey, J., Fender, R. P., Tudose, V. and Nicolson, G. D. (2007), Detection of compact radio emission from Circinus X-1 with the first Southern hemisphere e-VLBI experiment. Monthly Notices of the Royal Astronomical Society: Letters, 380: L11–L14. doi: 10.1111/j.1745-3933.2007.00339.x

Author Information

  1. 1

    CSIRO Australia Telescope National Facility, PO Box 76, Epping, NSW, Australia

  2. 2

    Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail H39, PO Box 218, Hawthorn, VIC, Australia

  3. 3

    School of Mathematics and Physics, University of Tasmania, Private Bag 21, Hobart 7001, TAS, Australia

  4. 4

    School of Physics and Astronomy, University of Southampton, High Field SO17 1BJ

  5. 5

    Astronomical Institute ‘Anton Pannekoek’, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

  6. 6

    Astronomical Institute of the Romanian Academy, Cutitul de Argint 5, RO-040557 Bucharest, Romania

  7. 7

    Hartebeesthoek Radio Astronomy Observatory, PO Box 443, Krugersdorp 1740, South Africa

* E-mail: Chris.Phillips@csiro.au

Publication History

  1. Issue published online: 16 JUL 2007
  2. Article first published online: 6 JUL 2007
  3. Accepted 2007 May 17. Received 2007 May 14; in original form 2007 April 12

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Keywords:

  • instrumentation: interferometers;
  • techniques: interferometric;
  • radio continuum: stars;
  • X-rays: stars;
  • X-rays: individual: Circinus X-1

ABSTRACT

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.

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