X-ray observations of the Seyfert galaxy LB 1727 (1H 0419-577)

We discuss the properties of the Seyfert 1.5 galaxy LB 1727, also known as 1H 0419 - 577, from X-ray observations obtained by ASCA and ROSAT, along with optical observations from earlier epochs, The source flux was F2-10 similar or equal to 10(-11) ergs cm(-2) s(-1) during the ASCA observations that were carried out during 1996 July-August, and we find only modest (less than or similar to 20%) variations in the Bur in this band within or between these observations. In contrast, a daily monitoring campaign over 1996 June-September by the ROSAT HRI instrument reveals the soft X-ray (0.1-2 keV) flux to have increased by a factor of similar or equal to 3. Significant: variations were also observed down to timescales of similar to 40 ks. We find that the 2-10 keV continuum can be parameterized as a power law with a photon index Gamma similar to 1.45-1.68 across similar to 0.7-11 keV in the rest frame. We also report the first detection of iron Ka line emission in this source. Simultaneous ASCA and ROSAT data show the X-ray spectrum to steepen sharply at a rest energy similar to 0.75 keV, so the spectrum below this energy can be parameterized as a power law of slope Gamma similar to 3.6. The X-ray emission appears to be unattenuated, and we find that ionized gas alone cannot produce such a sharp spectral break. Even allowing the presence of such gas, the simultaneous ASCA and HRI data demonstrate that the underlying continuum is required to steepen below similar to 0.75 keV. Thus LB 1727 is one of the Few Seyferts for which we can rule out the possibility that the presence of a warm absorber is solely responsible for the spectral steepening in the soft X-ray regime. Consideration of the overall spectral energy distribution for this source indicates the presence of a pronounced XUV bump visible in optical, ultraviolet, and soft X-ray data. The source appears relatively weak in infrared emission; and so if dust exists in the source, it is not excited by the nuclear radiation.