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Karen M. Leighly 《Astrophysics and Space Science》2005,300(1-3):137-142
Significant (marginal) detections of periodic signals have been recently reported in 3 (4) Active Galactic Nuclei. Three of
the detections were obtained from long EUVE light curves of moderate-luminosity Seyfert galaxies; the fourth was discovered
in Chandra data from the low-luminosity Seyfert 1 galaxy NGC 4395. When compared with Cyg X-1, I find that the period is related
to the luminosity as P∝ L2/3 rather than the expected one-to-one relationship. This result might be explained if the QPO is associated with the inner
edge of the optically thick accretion disk, and the inner-edge radius depends on the source luminosity (or black hole mass).
A discussion of uncertainties in the period detection methodology is also discussed. 相似文献
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John Leighly 《The Professional geographer》1987,39(4):405-412
Carl Sauer's writings contain material related to the general concept of “human ecology,”but he used the term infrequently and without emphasis and mainly as an analogy or metaphor. 相似文献
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Wang Otani Cappi Leighly Brinkmann & Matsuoka 《Monthly notices of the Royal Astronomical Society》1998,293(4):397-404
Results of ASCA and ROSAT observations of the Seyfert 1 galaxy RX J0437.4−4711 are presented. The X-ray continuum spectrum can be described by the sum of a power law with photon index 2.15 ± 0.04 and a soft emission component characterized by a blackbody with temperature 29 ± 2 eV. The total luminosity of the soft component is larger than that of the power-law component if the power law is cut off around a few hundred keV. A weak absorption edge with τ = 0.26 ± 0.13 at the rest-frame energy of E = 0.83 ± 0.05 keV and an Fe Kα line with EW = 430 ± 220 eV at an energy E = 6.47 ± 0.15 keV are also detected. The X-ray flux showed a 47 per cent increase between two ASCA observations 4 months apart, but no spectral variability was seen. We argue that reprocessing of the hard X-ray emission cannot produce all the soft X-ray emission, since the total luminosity of the soft component is larger than that of the integrated power-law component. Similarities with some stellar black hole candidates are briefly discussed. 相似文献
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F. Fiore G. Matt M. Cappi M. Elvis K. M. Leighly F. Nicastro L. Piro A. Siemiginowska & B. J. Wilkes 《Monthly notices of the Royal Astronomical Society》1998,298(1):103-113
Steep soft X-ray (0.1–2 keV) quasars share several unusual properties: narrow Balmer lines, strong Fe II emission, large and fast X-ray variability, and a rather steep 2–10 keV spectrum. These intriguing objects have been suggested to be the analogues of Galactic black hole candidates in the high, soft state. We present here results from ASCA observations for two of these quasars: NAB 0205 + 024 and PG 1244 + 026. Both objects show similar variations (factor of ∼ 2 in 10 ks), despite a factor of ∼ 10 difference in the 0.5–10 keV luminosity (7.3 × 1043 erg s−1 for PG 1244 + 026 and 6.4 × 1044 erg s−1 for NAB 0205 + 024, assuming isotropic emission, H 0 = 50.0 and q 0 = 0.0). The X-ray continuum of the two quasars flattens by 0.5–1 going from the 0.1–2 keV band towards higher energies, strengthening recent results on another half-dozen steep soft X-ray active galactic nuclei. PG 1244 + 026 shows a significant feature in the '1-keV' region, which can be described either as a broad emission line centred at 0.95 keV (quasar frame) or as edge or line absorption at 1.17 (1.22) keV. The line emission could be a result of reflection from a highly ionized accretion disc, in line with the view that steep soft X-ray quasars are emitting close to the Eddington luminosity. Photoelectric edge absorption or resonant line absorption could be produced by gas outflowing at a large velocity (0.3–0.6 c ). 相似文献
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Yasushi Ikebe Karen Leighly Yasuo Tanaka Takao Nakagawa Yuichi Terashima Stefanie Komossa 《Monthly notices of the Royal Astronomical Society》2000,316(2):433-441
We present new data taken at 850 μm with SCUBA at the James Clerk Maxwell Telescope for a sample of 19 luminous infrared galaxies. Fourteen galaxies were detected. We have used these data, together with fluxes at 25, 60 and 100 μm from IRAS , to model the dust emission. We find that the emission from most galaxies can be described by an optically thin, single temperature dust model with an exponent of the dust extinction coefficient ( k λ ∝ λ − β ) of β ≃1.4–2. A lower β ≃1 is required to model the dust emission from two of the galaxies, Arp 220 and NGC 4418. We discuss various possibilities for this difference and conclude that the most likely is a high dust opacity. In addition, we compare the molecular gas mass derived from the dust emission, M 850 μm , with the molecular gas mass derived from the CO emission, M CO , and find that M CO is on average a factor 2–3 higher than M 850 μm . 相似文献
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