BeppoSAX spectroscopy of MR 2251-178: A test for ionized reflection in radio quiet QSOs

We present the 0.1-200 keV BeppoSAX spectrum of MR 2251-178observed at two epochs in 1998 separated by 5 months. Both epochs show identical spectral shape and X-ray flux. Analysis of the combined spectra allow us to confirm the presence of the ionized Fe Kalpha line detected by ASCA and to test the presence of reflection from ionized material. The best self-consistent spectral fit is obtained when including a contribution from a mildly ionized reflector (xi _0.01-100 ~ 1625 erg cm s^-1, i.e. U_0.1-10 ~ 0.14) with a reflection fraction R_ion ~ 0.11. An exponential cut-off to the direct power-law continuum is then required at E ~ 100 keV. The low energy spectrum is absorbed by ionized matter with a column density N_W = (8.1_-1.2^+2.1) x 10²¹ cm^-2 and an X-ray ionization parameter U_0.1-10= 0.06 +/- 0.01. The warm absorber column is slightly lower than that measured with ASCA. This change could be caused by bulk motion. The BeppoSAX absorber ionization parameter globally agrees with the ``U versus Flux'' correlation found for MR 2251-178 with EXOSAT, Ginga and ASCA. This suggests that the absorber is in a state of instantaneous ionization equilibrium....