космического рентгеновского фона: томография крупномасштабной структуры
Вселенной при помощи флуоресцентной линии железа 6.4 кэВ.
На конкурс представлена статья:
G.Huetsi, M.Gilfanov, R.Sunyaev
Angular fluctuations in the CXB: Is Fe 6.4 keV line tomography of the large-scale structure feasible?
Astronomy and Astrophysics, 2012, accepted for publication
AGN are known to account for a major fraction,
if not all, of the Cosmic X-ray background radiation. The dominant sharp
spectral feature in their spectra is the 6.4 keV
fluorescent line of iron, which may contribute as much as ~ 5-10% to the CXB
spectral intensity at ~ 2-6 keV. Due to cosmological redshift, the line photons detected at the energy E carry information
about objects located at the redshift z=6.4/E-1. In
particular, imprinted in their angular fluctuations is the information about
the large-scale structure at redshift z. This opens a
possibility to perform the Fe K_alpha line tomography
of the cosmic large-scale structure. We investigate the feasibility of the Fe K_alpha line tomography of the large-scale structure and show
that detection of the tomographic signal at a ~100
sigma confidence requires an all-sky survey by an instrument with effective
area of ~10 m^2 and field of view of ~1 deg^2. The signal is strongest for
objects located at the redshift z~1, and at the
angular scales corresponding to l ~ 100-300, therefore an optimal detection can
be achieved with an instrument having a rather modest angular resolution of ~
0.1-0.5 deg. For such an instrument, the CCD-type energy resolution of ~
100-200 eV FWHM is entirely sufficient for the
optimal separation of the signals originating at different redshifts.
The gain in the signal strength which could potentially be achieved with energy
resolution comparable to the line width, is nullified
by the photon counting and AGN discreteness noise. Among the currently planned
and proposed missions, these requirements are best satisfied by LOFT, despite
the fact that it was proposed for entirely different purpose. Among others,
clear detection should be achieved by WFXT (~ 20-35 sigma)
and ATHENA (~ 10-20 sigma).