Large-scale attractors: the direct effect on the X-ray background.

We study the direct effect of large-scale inhomogeneities (they generate a velocity of ~500 km s^-1^ at the Local Group) on the X-ray background (XRB). These attractors can have different geometrical forms (spheres, discs and filaments) and can be immersed in different populations of X-ray emitters ( > 2 keV). A fit of the observed X-ray intensity excess (after subtracting the galactic and dipole anisotropies) in directions near to that of our peculiar motion to the theoretical behaviours suggested in this work can be useful to determine the geometrical form and the position of our Great Attractor, and to impose constraints on the contribution of a determinate source population to the XRB. By considering a region with a radius of 20^deg^ around the direction of Hydra-Centaurus and another sky region with the same radius but opposed to the first one, we can calculate the mean value of the observed intensity differences between each pixel directed toward the dense region and the opposite region (we assume that the opposite region to that around the Great Attractor is a typical region of the XRB, i.e., it does not show a lack of intensity). Then, we compare our results with the recent observational result found by Jahoda & Mushotzky (once the dipole contribution has been subtracted). If {OMEGA}_0_ = 1, we conclude that the bright AGNs can produce all the XRB (independently of the types of Great Attractor that we consider), whereas the AGNs with low luminosity cannot generate all the XRB if the Great Attractor is either spherical or elongated. The permitted contributions to the XRB go from f_x_ <= 40 per cent if the attractor is moderately elongated and is placed at r_o_ = 150 h^-1^ Mpc, up to f_x_ < 80 per cent if the attractor is spherical and is placed at r_o) = 50 h^-1^ Mpc. If the attractor is flattened, the AGNs with low luminosity can produce all the XRB (independently of the distance of the attractor). Moreover, we also calculate the effective dipole (Compton-Getting effect modified by the direct of ~0.5 per cent. From this we conclude that the bright AGNs can generate all the XRB, whereas the AGNs with low luminosity only can produce f_x_ <~14 per cent (sphere), f_x_ <~ 8 per cent (moderately elongated structure) and f_x_ <~ 22-30 per cent (moderately flattened structure).