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Why do IXO?

High-energy phenomena in the X-ray band characterize the evolution of cosmic structures on both large and small scales.

On the smallest scales, X-rays provide the only electromagnetic spectral signatures from the regions of strong gravity near black holes through absorption and emission features, such as the Fe Kα emission line at 6.4 keV and its profile [Brenneman et al.], and can penetrate the surrounding gas and dust allowing us to uncover the earliest massive black holes and measure their distances [Nandra et al.]. In neutron stars, X-ray spectra and light curves carry the observable imprints of exotic processes occurring in these objects [Paerels et al.].

WFI Simulation of the Chandra Deep Field South with the Hubble Ultra Deep Field (HUDF) in inset. Simulated spectra of various sources are shown, illustrating IXO’s ability (clockwise from top left) to:

  1. Determine redshift autonomously in the X- ray band;
  2. Determine temperatures and abundances, even for low luminosity groups to z<1;
  3. Make spin measurements of AGN to a similar redshift;
  4. Uncover the most heavily obscured, Compton-thick AGN.

Click the image for a larger view.

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On the largest scales, X-rays are essential for detecting the “missing” half of baryons in the local Universe, as a probe of both dark energy and dark matter [Bregman et al.] and to measure the energy deposited in the surrounding medium by AGN’s jets and winds [Miller et al; Fabian et al.].

Building on a rich technological heritage, IXO will have improved instrumental capabilities in X-ray imaging, timing, and spectroscopy far beyond the current generation of X-ray missions (e.g. Chandra, XMM, RXTE, and Suzaku). Moreover, IXO will carry an X-ray polarimeter, which will open a new window on the study of high-energy phenomena. See Science Performance Requirements. These will enable observations that will address the above science issues—among others—with unprecedented detail and precision.

See also

IXO Science Goals
Science performance requirements
Before IXO: Con-X and XEUS »
IXO technology drivers »

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Selected White Papers submitted to the Astro2010 Decadal

  1. Spin and Relativistic Phenomena Around Black Holes, Brenneman et al.
  2. The Growth of Supermassive Black Holes Across Cosmic Time, Nandra et al.
  3. The Behavior of Matter Under Extreme Conditions, Paerels et al.
  4. The Cosmic Web of Baryons, Bregman et al.
  5. Fundamental Accretion and Ejection Astrophysics, Miller et al.
  6. Cosmic Feedback from Supermassive Black Holes, Fabian et al.

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