科研之友
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摘要
We present the results from exploratory (12-23 ks) XMM-Newton observations of six optically selected, radio-loud active galactic nuclei (AGNs), together with new radio data and a reanalysis of their archival SDSS spectra. The sources were selected in an effort to expand the current sample of radio-loud AGNs suitable for detailed X-ray spectroscopy studies. The sample includes three broad-line and three narrow-line sources, with X-ray luminosities of the order of L2-10 keV similar to 10(43) erg s(-1). The EPIC spectra of the broad-lined sources can be described by single power laws with photon indices Gamma similar to 1.6 and little to negligible absorption (N-H less than or similar to 10(21) cm(-2)); on the contrary, significant absorption is detected in the narrow-lined objects, N-H similar to 10(23) cm(-2), one of which displays a prominent (equivalent width similar to 2 keV) Fe K alpha emission line. Studying their location in several luminosity-luminosity diagrams for radio-loud AGNs, we find that the sources fall at the lower end of the distribution for bright, classical radio-loud AGNs and close to LINER-like sources. As such, and as indicated by the ratios of their optical emission lines, we conclude that the sources of our sample fall on the border between radiatively efficient and inefficient accretion flows. Future deeper studies of these targets at X-rays and longer wavelengths will expand our understanding of the central engines of radio-loud AGNs at a critical transition region.
- 出版日期2011-7
