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The variable ROSAT X-ray spectrum of the BL Lac 0716+714

M. Cappi·A. Comastri·S. Molendi·G. G. C. Palumbo·R. Della Ceca·T. Maccacaro
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Abstract

The BL Lac object 0716+714 is a powerful flat spectrum radio source detected by CGRO-EGRET at $γ$-ray energies. It has been observed for about 21000 s over two days by the X-ray telescope onboard the ROSAT satellite and strong flux and spectral variations have been detected. In the time scale of two days the source varied by a factor of $\sim 7$; during a sudden ($\sim 1000$ s) flux increase, the variation was 70\%. 0716+714 exhibits spectral variations related to source flux variability which may be attributed to a ``soft excess" component most prominent when the source was in a low state. The spectrum of 0716+714 steepened in the soft X-ray band when the flux decreased while in the hard X-ray band remained constant. A double power law model, representing steep synchrotron radiation at low energies and flat inverse Compton radiation above $\sim$ 1 keV, best fits both the low and high state.

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M. Cappi, A. Comastri, S. Molendi, G. G. C. Palumbo, R. Della Ceca, T. Maccacaro. 1994-09-27. The variable ROSAT X-ray spectrum of the BL Lac 0716+714. https://doi.org/10.1093/mnras%2F271.2.438

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