Circinus X-1 is an X-ray binary star system that includes a neutron star. Observation of Circinus X-1 in July 2007 revealed the presence of X-ray jets normally found in black hole systems; it is the first of the sort to be discovered that displays this similarity to black holes. Circinus X-1 may be among the youngest X-ray binaries observed.
On June 14, 1969, an Aerobee 150 rocket, launched from Natal, Rio Grande do Norte, Brazil, obtained X-ray data during a scan of the Norma-Lupus-Circinus region that detected a well-isolated source at ℓ = 321.4±0.9° b = -0.5±2° (galactic), RA 15h 14m Dec −57° 49′ within the constellation Circinus and referred to as Circinus XR-1 (Cir XR-1). The distance of Circinus X-1 is not well established with a low estimate of 13,400 light years, mid-estimate of 18,000 light years, and high estimate of 26,000 light years.
A 16.6 day X-ray period was found by Kaluzienski et al. The X-ray source is assumed to be a neutron star as part of a low-mass X-ray binary (LMXB), type-I X-ray burster. The X-ray and radio nebulae surrounding Circinus X-1 have properties consistent with a young supernova remnant. This rare case of an X-ray binary apparently associated with a supernova remnant suggests the binary is very young on cosmic time scales, possibly less than 4600 years old. An association of Circinus X-1 with a different nearby supernova remnant, G321.9-0.3, has been ruled out.
Other spectral regions
The binary nature of Cir X-1 has been established. The binary's radio component and a possible visual counterpart were identified by Whelan et al. Its infrared counterpart was located and found to flare with a 16.6d period by Glass. A (heavily reddened) precise optical counterpart (now known as BR Cir) was identified by Moneti.
- Margon B, Lampton M, Bowyer S, Cruddace R (Oct 1971). "A Pulsing X-Ray Source in Circinus". Ap J. 169 (10): L23–5. Bibcode:1971ApJ...169L..23M. doi:10.1086/180806.
- R. Iaria, M. Spano, T. DiSalvo, N.R. Robba, L. Burderi, R. Fender, M. Van Der Klis, F. Frontera (January 2005). "ON THE SOFT EXCESS IN THE X-RAY SPECTRUM OF CIRCINUS X-1: REVISITATION OF THE DISTANCE TO CIRCINUS X-1". The Astrophysical Journal 619 (1): 503–516. doi:10.1086/426422. Retrieved 5 December 2013.
- Guaqiang Ding, Chunping Huang, Jinlu Qu (2012). "The Orbital Modulation for the Spectrum and Mass Accretion Rate in Circinus X-1". International Journal of Astronomy and Astrophysics 2 (4): 26296. doi:10.4236/ijaa.2012.24033. Retrieved 5 December 2013.
- "Circinus X-1: Neutron Stars Join The Black Hole Jet Set". Harvard-Smithsonian Center for Astrophysics. Retrieved 5 December 2013.
- Kaluzienski, L. J.; Holt, S. S.; Boldt, E. A.; Serlemitsos, P. J. (1976). "Evidence for a 16.6 day period from Circinus X-1". Astrophysical Journal 208: L71–L75. Bibcode:1976ApJ...208L..71K. doi:10.1086/182235.
- Mignani RP, De Luca A, Caraveo PA, Mirabel IF (2002). "HST observations rule out the association between Cir X-1 and SNR G321.9-0.3". Astron Astrophys. 386 (2): 487–91. arXiv:astro-ph/0202268. Bibcode:2002A&A...386..487M. doi:10.1051/0004-6361:20020224.
- S. Heinz, P. Sell, R.P. Fender, P.G. Jonker, W.N. Brandt, D.E. Calvelo-Santos, A.K. Tzioumis, M.A. Nowak, N.S. Schulz, R. Wijnands, M. Van Der Klis (December 2013). "The Youngest Known X-ray Binary: Circinus X-1 and its Natal Supernova Remnant". The Astrophysical Journal 779 (2). doi:10.1088/0004-637X/779/2/171. Retrieved 5 December 2013.
- Jones C, Tananbaum H, Giacconi R (1973). 141st Meeting Amer Astron Soc (Tucson, Arizona).
- Whelan, J. A. J.; Mayo, S. K.; Wickramasinghe, D. T.; Murdin, P. G.; Peterson, B. A.; Hawarden, T. G.; Longmore, A. J.; Haynes, R. F.; Goss, W. M.; Simons, L. W.; Caswell, J. L.; Little, A. G.; McAdam, W. B. (1977). Monthly Notices of the Royal Astronomical Society 161: 259–271.
- Glass, I.S. (1978). "Variations of Circinus X-1 in the infrared". Monthly Notices of the Royal Astronomical Society 183: 335–340. Bibcode:1978MNRAS.183..335G.
- Moneti, A. (1992). "Optical and infrared observations of Circinus X-1". Astronomy and Astrophysics 260: L7–L10. Bibcode:1992A&A...260L...7M.
- "Circinus X-1: Neutron Stars Join the Black Hole Set". Chandra X-Ray Observatory. Harvard University / National Aeronautics and Space Administration. 2007. Retrieved 8 January 2009.
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