  We propose a possible way to detect baryons at low redshifts from the
analysis of X-ray absorption spectra of bright AGN pairs. A simple
semi-analytical model to simulate the spectra is presented. We model the
diffuse warm-hot intergalactic medium (WHIM) component, responsible for the
X-ray absorption, using inputs from high-resolution hydro-dynamical simulations
and analytical prescriptions. We show that the number of OVII absorbers per
unit redshift with column density larger than $10^{13.5}$ cm$^{-2}$ -
corresponding to an equivalent width of $\sim$ 1 km/s - which will be possibly
detectable by {\it XEUS}, is $\magcir 30$ per unit redshift. {\it
Constellation-X} will detect $\sim 6$ OVII absorptions per unit redshift with
an equivalent width of 10 km/s. Our results show that, in a $\Lambda$CDM
Universe, the characteristic size of these absorbers at $z\sim 0.1$ is $\sim 1$
$h^{-1}$ Mpc. The filamentary structure of WHIM can be probed by finding
coincident absorption lines in the spectra of background AGN pairs. We estimate
that at least 20 AGN pairs at separation $\mincir 20$ arcmin are needed to
detect this filamentary structure at a 3$\sigma$ level. Assuming observations
of distant sources using {\it XEUS} for exposure times of 500 ksec, we find
that the minimum source flux to probe the filamentary structure is $\sim
2\times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$, in the 0.1-2.4 keV energy band. Thus,
most pairs of these extragalactic X-ray bright sources have already been
identified in the {\it ROSAT} All-Sky Survey. Re-observation of these objects
by future missions could be a powerful way to search for baryons in the low
redshift Universe.
