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 MR2251-178 observed at two epochs in 1998 separated by 5 months. Both epochs show identical spectral s hape and X-ray flux. Analysis of the combined spectra allow us to confirm t he presence of the ionized Fe K alpha line detected by ASCA and to test the presence of reflection from ionized material. The best self-consistent spe ctral fit is obtained when including a contribution from a mildly ionized r eflector (xi (0.01-100) similar to 1625 erg cm s(-1), i.e.U0.1-10 similar t o 0.14) with a reflection fraction R-ion similar to 0.11. An exponential cu t-off to the direct power-law continuum is then required at E similar to 10 0 keV. The low energy spectrum is absorbed by ionized matter with a column density N-W = (8.1(-1.2)(+2.1)) similar to 10(21) cm(-2) and an X-ray ioniz ation parameter U0.1-10 = 0.06+/-0.01. The warm absorber column is slightly lower than that measured with ASCA. This change could be caused by bulk mo tion. The BeppoSAX absorber ionization parameter globally agrees with the " U versus Flux" correlation found for MR2251-178 with EXOSAT, Ginga and ASCA . This suggests that the absorber is in a state of instantaneous ionization equilibrium.