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|a Corrales, Lia
|e author
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|a MIT Kavli Institute for Astrophysics and Space Research
|e contributor
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|a Corrales, Lia
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|a X-RAY SCATTERING ECHOES AND GHOST HALOS FROM THE INTERGALACTIC MEDIUM: RELATION TO THE NATURE OF AGN VARIABILITY
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|b IOP Publishing,
|c 2015-09-01T20:43:10Z.
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|z Get fulltext
|u http://hdl.handle.net/1721.1/98313
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|a X-ray bright quasars might be used to trace dust in the circumgalactic and intergalactic medium through the phenomenon of X-ray scattering, which is observed around Galactic objects whose light passes through a sufficient column of interstellar gas and dust. Of particular interest is the abundance of gray dust larger than 0.1 µm, which is difficult to detect at other wavelengths. To calculate X-ray scattering from large grains, one must abandon the traditional Rayleigh-Gans approximation. The Mie solution for the X-ray scattering optical depth of the universe is ~1%. This presents a great difficulty for distinguishing dust scattered photons from the point source image of Chandra, which is currently unsurpassed in imaging resolution. The variable nature of AGNs offers a solution to this problem, as scattered light takes a longer path and thus experiences a time delay with respect to non-scattered light. If an AGN dims significantly ([> over ~]3 dex) due to a major feedback event, the Chandra point source image will be suppressed relative to the scattering halo, and an X-ray echo or ghost halo may become visible. I estimate the total number of scattering echoes visible by Chandra over the entire sky: N[subscript ech] ~ 10[superscript 3](ν[subscript fb]/yr[superscript -1]), where ν[subscript fb] is the characteristic frequency of feedback events capable of dimming an AGN quickly.
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|a United States. National Aeronautics and Space Administration (Earth and Space Science Fellowship Program Grant NNX11AO09H)
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|a en_US
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|a Article
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|t The Astrophysical Journal
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