EDP Sciences
Free access
Volume 371, Number 1, May III 2001
Page(s) 93 - 96
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010336

A&A 371, 93-96 (2001)
DOI: 10.1051/0004-6361:20010336

A new mechanism for soft X-ray excess in NGC 5548

Tong-Sheng Xia and Jia-Lü Zhang

Center for Astrophysics, University of Science and Technology of China, Hefei, 230026 Anhui, PR China National Astronomical Observatories, Chinese Acadamy of Sciences (NAOCAS), 100012 Beijing, PR China

(Received 20 November 2000 / Accepted 12 January 2001 )

Many active galaxies exhibit soft X-ray excess in the 0.2-2 keV band with a photon index $\alpha _\mathrm{s} \sim 2.38 \pm 0.25$, much higher than that of the hard X-ray (2-10 keV) band with $\alpha
_\mathrm{h} \sim 1.7$. Different theoretical models have been proposed to reproduce and explain the spectra, but the complexity of all these models tends to make the situation even more confused. Here we present results using our newly-proposed synchro-curvature mechanism, which we show can reproduce the soft X-ray excess by a simple fitting process. Such a model may be helpful in considering the physical processes taking place in these objects.

Key words: galaxies: individual: NGC 5548 -- radiation mechanisms: non-thermal -- magnetic fields -- X-rays: galaxies

Offprint request: J.-L. Zhang, jlz@ustc.edu.cn

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