2000 Fiscal Year Final Research Report Summary
Revealing central quasar stracture by gravitational lensing
| Project/Area Number |
10640228
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Astronomy
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
HIUESHIGE Shin KYOTO UNIVERSITY, Graduate School of Assoc, Science prof., 大学院・理学研究科, 助教授 (70229780)
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| Project Period (FY) |
1998 – 2000
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| Keywords | black hole / quasar / active golactic naclei / gravitational lens / accaetion disk / high energy emission / magaetic fields / fractal |
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| Research Abstract |
When a low-mass object (e.g., a star) causes gravitational lensing to the image of some object, radiation from a part of the source will be greatly enhanced (so-called microlens event). By using this phenomenon, we can observationally resolve the central structure of active galactic nuclei (quasars). The ideal target is Q2237+0305, Einstein Cross.
This is composed of 4 images with a cross shape as a result of a gravitational lensing of a distant quasar (z=1.69) by a nearby galaxy (z=0.04). When a star in the lesning galaxy passes just in front of one of the images of the quasar, that image will be brightened largely. Since the resultant light curve sensitively depends on the size and brightness profile of the source image, we can extract information regarding quasar disk structure from the microlens light curves. Such microlens events have been observed several times in the Einstein-Cross.
We first constructed the optically thick standard disk and optically thin advection-dominated flow (ADAF) models and calculated the expected microlens light curves, finding that for the latter case little color changes occur and radiation from the vicinity of the black hole dominates over the entire radiation.
However, the optically thin ADAF model can apply only to low luminosity sources. We, next, constructed a disk-corona model which can reproduce the observed quasar spectra and calculated expected microlens light curves. As a result, soft and hard X-rays exhibit distinct variations and the difference contains an essential feature of the model. We also developped an inversion technique ; namely, how to reconstruct brightness profiles from microlens light curves.
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