2000/06/23 by K. Nandra, T. Le, Truong Le +6 · 6 citations
Engineering · Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Bremsstrahlung #Calibration and Measurement Techniques #Compton scattering #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Optics #Photon #Physics #ROSAT #Soft photon #Spectral line #astro-ph
paper · pdf · doi:10.1086/317237
31 pages, 7 figures. LaTeX with encapsulated postscript. To appear in the Astrophysical Journal. Also available via http://lheawww.gsfc.nasa.gov/users/nandra/pubs/7469_spectral/abstract.html
arxiv created 2000/06/23 · openalex publication_date 2000/12/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We present a spectral analysis of a ~30 day, near-continuous observation of the Seyfert 1 galaxy NGC 7469 with RXTE . Daily integrations show strong spectral changes during the observation. Our main result is that we find the X-ray spectral index to be correlated with the UV flux. Furthermore, the broadband X-ray photon flux is also correlated with the UV continuum. These correlations point toward a model in which the X-rays originate via thermal Comptonization of UV seed photons. Furthermore, the UV is also correlated with the extrapolation of the X-ray power law into the soft X-ray/EUV region. Our data analysis therefore reopens the possibility that the UV photons and their variability arise from reprocessing, as long as the primary source of heating is photoelectric absorption in the reprocessor, rather than Compton downscattering. A coherent picture of the X-ray/UV variability can therefore be constructed whereby absorption and reprocessing of EUV/soft X-rays in a standard accretion disk produce a variable seed photon distribution, which is in turn upscattered into the X-ray band. We also find a significant correlation between the 2-10 keV flux and the 6.4 keV iron Kα line, suggesting that at least some portion of the line originates within ~1 light day of the X-ray continuum source. Neither the power-law photon index nor the Compton reflection component are correlated with the 2-10 keV flux. The latter is not correlated with the iron Kα line flux either. We do find an apparent correlation between the X-ray spectral index and the strength of the Compton reflection component. In an Appendix we show, however, that this can be produced by a combination of statistical and systematic errors. We conclude that the apparent variations in the Compton reflection component may be an artifact of these effects.