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A faint discrete source origin for the highly ionized iron emission from the Galactic Centre region


The origin of the X-ray emission for the central region of our Galaxy has remained a mystery1,2,3,4. In particular, the relative spectral contributions of the diffuse emission and discrete sources, which are critical to understanding the high-energy phenomena in this environment, have been unclear because of the lack of sufficient spatial resolution. Here we report the results of a large-scale imaging survey of the Galactic Centre that resolves these components. We find that the Kα emission from iron that has been highly ionized (so that it has only two electrons left), which has previously been attributed to the diffuse component1, actually arises mainly from discrete sources. This suggests that the presence of a large amount of hot gas (T ≈ 108 K) is no longer required to explain the iron line emission. The spectra of the discrete sources indicate the presence of numerous accreting white dwarfs, neutron stars, and/or black holes in the region. The diffuse emission dominates over the contribution from the faint point sources, and is shown to be associated globally with interstellar features that have been observed at radio and mid-infrared wavelengths, suggesting that it is the product of recent massive star formation.

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Figure 1: Mosaic image of the Galactic Centre region.
Figure 2: Comparison of accumulated point-source (lower) and diffuse emission (upper) spectra.
Figure 3: A multiwavelength close-up of the recent massive star-forming region near the Galactic centre.


  1. Koyama, K. et al. ASCA view of our Galactic center: Remains of past activities in X-rays? Publ. Astron. Soc. J. 48, 249–255 (1996).

    Article  ADS  CAS  Google Scholar 

  2. Sidoli, L. & Mereghetti, S. The X-ray diffuse emission from the Galactic center. Astron. Astrophys. 349, L49–L52 (1999).

    ADS  CAS  Google Scholar 

  3. Valinia, A. et al. On the origin of the iron K line in the spectrum of the Galactic X-ray background. Astrophys. J. 543, 733–739 (2000).

    Article  ADS  CAS  Google Scholar 

  4. Tanaka, Y., Koyama, K., Maeda, Y. & Sonobe, T. Unusual properties of X-ray emission near the Galactic center. Publ. Astron. Soc. J. 52, L25–L30 (2000).

    Article  ADS  CAS  Google Scholar 

  5. Wang, Q. D., Gotthelf, E. V., Lang, C. & Jagodzinski, F. UMass/Columbia Chandra X-ray survey of the Galactic center region. Astrophys. J. (submitted).

  6. Sidoli, L., Belloni, T. & Mereghetti, S. A catalogue of soft X-ray sources in the Galactic center region. Astron. Astrophys. 368, 835–844 (2001).

    Article  ADS  Google Scholar 

  7. Sakano, M. et al. ASCA X-ray source catalogue in the Galactic center region. Astrophys. J. Suppl. Ser (in the press); also as preprint astro-ph/0108376 at 〈〉 (2001).

  8. Ebisawa, K. et al. Origin of the hard X-ray emission from the Galactic plane. Science 293, 1633–1635 (2001).

    Article  ADS  CAS  Google Scholar 

  9. Barret, D. et al. Hard X-ray emission from low-mass X-ray binaries. Astrophys. J. 533, 329–351 (2000).

    Article  ADS  Google Scholar 

  10. Feng, Y. X. et al. Evolution of iron Kα: Line emission in the black hole candidate GX339-4. Astrophys. J. 553, 394–398 (2001).

    Article  ADS  CAS  Google Scholar 

  11. Yusef-Zadeh, F. et al. Detection of X-ray emission from the Arches cluster near the Galactic center. Astrophys. J. (in the press); also as preprint astro-ph/0108174 at 〈〉 (2001).

  12. Baganoff, F. et al. Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre. Nature 413, 45–48 (2001).

    Article  ADS  CAS  Google Scholar 

  13. Murakami, H., Koyama, K. & Maeda, Y. Chandra observations of diffuse X-rays from the Sagittarius B2 cloud. Astrophys. J. 558, 687–692 (2001).

    Article  ADS  CAS  Google Scholar 

  14. Maeda, Y. et al. A Chandra study of Sgr A East: A supernova remnant regulating the activity of our Galactic center? Astrophys. J. (in the press).

  15. Jackson, J. M., Heyer, M. H., Paglione, T. & Bolatto, A. HCN and CP in the central 630 parsecs of the Galaxy. Astrophys. J. 456, L91–L95 (1996).

    Article  ADS  CAS  Google Scholar 

  16. Price, S. D. et al. Midcourse space experiment of the Galactic plane. Astrophys. J. 121, 2819–2842 (2001).

    Google Scholar 

  17. Fromerth, M. J., Melia, F. & Leahy, D. A. A Monte Carlo study of the 6.4 keV emission at the Galactic center. Astrophys. J. 547, 129–132 (2001).

    Article  ADS  Google Scholar 

  18. Tsuboi, M., Ukita, N. & Handa, T. An expanding shell-like molecular cloud near the Galactic center arc. Astrophys. J. 481, 263–266 (1997).

    Article  ADS  CAS  Google Scholar 

  19. Yusef-Zadeh, F., Wardle, M. & Parastaran, P. The nature of the Faraday screen toward the Galactic center nonthermal filament G359.54+0.18. Astrophys. J. 475, 119–122 (1997).

    Article  ADS  Google Scholar 

  20. Boggs, S. E. et al. Diffuse galactic soft gamma ray emission. Astrophys. J. 544, 320–329 (2000).

    Article  ADS  CAS  Google Scholar 

  21. Figer, D. et al. Hubble Space Telescope/NICMOS observations of massive stellar clusters near the Galactic center. Astrophys. J. 525, 750–758 (1999).

    Article  ADS  Google Scholar 

  22. Wang, Q. D. Structure and evolution of hot gas in 30 Dor. Astrophys. J. 510, L139–L143 (1999).

    Article  ADS  Google Scholar 

  23. Almy, R. C., McCammon, D., Digel, S. W., Bronfman, L. & May, J. Distance limits on the bright X-ray emission toward the Galactic center: Evidence for a very hot interstellar medium in the Galactic X-ray bulge. Astrophys. J. 545, 290–300 (2000).

    Article  ADS  CAS  Google Scholar 

  24. Sofue, Y. Bipolar hypershell Galactic center starburst model: further evidence from ROSAT data and new radio and X-ray simulations. Astrophys. J. 540, 224–235 (2000).

    Article  ADS  Google Scholar 

  25. Townsley, L. K., Broos, P. S., Garmire, G. & Nousek, J. Mitigating charge transfer inefficiency in the Chandra X-ray observatory advanced CCD imaging spectrometer. Astrophys. J. 534, L139–L142 (2000).

    Article  ADS  CAS  Google Scholar 

  26. Yusef-Zadeh, F., Morris, M. & Chance, D. Large, highly organised radio structures near the galactic centre. Nature 310, 557–561 (1984).

    Article  ADS  Google Scholar 

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We thank F. Jagodzinski for assistance in the data calibration, and L. Townsley for helping with the CTI corrections.

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Correspondence to Q. D. Wang.

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Wang, Q., Gotthelf, E. & Lang, C. A faint discrete source origin for the highly ionized iron emission from the Galactic Centre region. Nature 415, 148–150 (2002).

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