Hostname: page-component-7c8c6479df-7qhmt Total loading time: 0 Render date: 2024-03-28T09:51:33.129Z Has data issue: false hasContentIssue false

The Sources of the Hard X-Ray Background

Published online by Cambridge University Press:  25 May 2016

Giancarlo Setti
Affiliation:
Dipartimento di Astronomia, Università di Bologna, Osservatorio Astronomico di Bologna, Istituto di Radioastronomia del CNR, Via P. Gobetti, 101 - 40129 Bologna - Italy
Andrea Comastri
Affiliation:
Dipartimento di Astronomia, Università di Bologna, Osservatorio Astronomico di Bologna, Istituto di Radioastronomia del CNR, Via P. Gobetti, 101 - 40129 Bologna - Italy

Extract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The hard component (3 keV – ~ MeV) of the X-ray background (XRB) comprises the largest portion, ~ 90%, of the overall XRB intensity. The observed isotropy (the entire Galaxy is transparent above 3 keV) provides a prima facie evidence of its prevailing extragalactic nature. A large fraction (~ 75%) of the energy flux falls in the 3 – 100 keV band, the corresponding energy density being ≃ 5×10−5 eV cm−3, of which 50% is confined to the narrower 3 – 20 keV band. Although the energy flux carried by the XRB is relatively small compared to other extragalactic backgrounds, it was soon realized that it cannot be accounted for in terms of sources and processes confined to the present epoch. An analysis of the combined observed spectra (Gruber 1992) concludes that, while a thermal bremsstrahlung with an e-folding energy = 41.13 keV accurately fits the data up to 60 keV, above this energy the sum of two power laws is required with normalizations such that at 60 keV the spectral index is ~ 1.6, gradually flattening to ~ 0.7 at MeV energies. It should also be noted that below 10 keV the XRB energy spectrum is well represented by a power law of index α = 0.4 (IE−α).

Type
Part I: Invited Reviews
Copyright
Copyright © Kluwer 1996 

References

Allen, S.W. & Fabian, A.C. 1992, Mon. Not. R. astr. Soc., 258, 29P.CrossRefGoogle Scholar
Antonucci, R.R.J. & Miller, J.S. 1985, Astrophys. J., 297, 621.Google Scholar
Awaki, H., Koyama, K., Inoue, H., Halpern, J.P. 1991, Pub. Astr. Soc. Japan, 43, 195.Google Scholar
Barcons, X. & Fabian, A.C. 1988, Mon. Not. R. astr. Soc., 230, 189.Google Scholar
Barthel, P.D. 1989, Astrophys. J., 336, 606.Google Scholar
Boyle, B.J., et al. 1993, Mon. Not. R. astr. Soc., 260, 49.CrossRefGoogle Scholar
Comastri, A., Setti, G., Zamorani, G., Hasinger, G. 1994, Astron. Astrophys., in press.Google Scholar
Della Ceca, R., Maccacaro, T., et al. 1992, Astrophys. J., 389, 491.Google Scholar
Fabian, A.C., George, I.M., Miyoshi, S., Rees, M.J. 1990, Mon.Not.R.astr. Soc., 242, 14P.Google Scholar
Giacconi, R. & Zamorani, G. 1987, Astrophys. J., 313, 20.CrossRefGoogle Scholar
Gruber, D.E. 1992, in The X-ray background, eds. Barcons, X. and Fabian, A.C. (Cambridge Univ. Press, Cambridge), p.44.Google Scholar
Hasinger, G., et al. 1993, Astron. Astrophys., 275, 1.Google Scholar
Hayashida, K. 1990, , Tokyo University, ISAS RN 466.Google Scholar
Huchra, J., & Burg, R. 1992, Astrophys. J., 393, 90.Google Scholar
Madau, P., Ghisellini, G., Fabian, A.C. 1993, Astrophys. J., 410, L7.Google Scholar
Madau, P., Ghisellini, G., Fabian, A.C. 1994, Mon. Not. R. astr. Soc., 270, L17.Google Scholar
Matsuoka, M., Piro, L., Yamauchi, M., Murakami, T. 1990, Astrophys. J., 361, 440.CrossRefGoogle Scholar
Matt, G. & Fabian, A.C. 1994, Mon. Not. R. astr. Soc., 267, 187.Google Scholar
Miyaji, T., Lahav, O., Jahoda, K., Boldt, E. 1994, Astrophys. J., in press.Google Scholar
Morisawa, K., Matsuoka, M., Takahara, F., Piro, L. 1990, Astron. Astrophys., 236, 299.Google Scholar
Nandra, K. & Pounds, K.A. 1994, Mon. Not. R. astr. Soc., 268, 405.CrossRefGoogle Scholar
Piccinotti, G., et al. 1982, Astrophys. J., 253, 485.CrossRefGoogle Scholar
Pounds, K.A., et al. 1990, Nature, 344, 132.Google Scholar
Rogers, R.D. & Field, G.B. 1991, Astrophys. J., 378, 117.Google Scholar
Schwartz, D.A. & Tucker, W.H. 1988, Astrophys. J., 332, 157.Google Scholar
Setti, G. & Woltjer, L. 1973, in IAU Symposium No. 55, X- and Gamma-Ray Astronomy, eds. Bradt, H. and Giacconi, R. (Reidel, Dordrecht), p.208.Google Scholar
Setti, G. 1992, in The X-ray background, eds. Barcons, X. and Fabian, A.C. (Cambridge Univ. Press, Cambridge), p.187.Google Scholar
Setti, G. & Woltjer, L. 1989, Astron. Astrophys., 224, L21.Google Scholar
Setti, G. & Woltjer, L. 1994, Astrophys. J. Suppl., 92, 629.Google Scholar
Shafer, R.A. 1983, , University of Maryland, NASA Tech.Mem. 85029.Google Scholar
Taylor, G.B. & Wright, E.L. 1989, Astrophys. J., 339, 619.Google Scholar
Terasawa, N. 1991, Astrophys. J., 378, L11.Google Scholar
Turner, T.J. & Pounds, K.A. 1989, Mon. Not. R. astr. Soc., 240, 833.Google Scholar
Warwick, R.S. & Stewart, G.C. 1989, in 23rd ESLAB Symposium, in Two-Topics in X-Ray Astronomy, ESA SP-296, Vol.2, p.727.Google Scholar
Wright, E.L., et al. 1994, Astrophys. J., 420, 450.CrossRefGoogle Scholar
Zdziarski, A.A., Zycki, P.T., Svensson, R., Boldt, E. 1993a, Astrophys. J., 405, 125.CrossRefGoogle Scholar
Zdziarski, A.A., Zycki, P.T., Krolik, J.H. 1993b, Astrophys. J., 414, L81.CrossRefGoogle Scholar