Mon. Not. R. Astron. Soc., 315, 77-81 (2000/June-2)
X-ray observations of the `composite' Seyfert/star-forming galaxy IRAS00317-2142.
Abstract (from CDS):
I present ASCA observations of IRAS00317-2142, one of the most luminous (Lx∼1043erg.s–1 at 0.1-2keV) of the `composite' class of galaxies. This enigmatic class of objects presents narrow-emission-line optical spectra classifying these galaxies as star forming on the basis of the diagnostic emission-line ratios; yet, the presence of weak Hα broad wings also suggests the presence of a weak or obscured AGN. The ASCA spectrum can be represented by a power law with a photon index of Γ=1.76±0.08. Strong long-term variability is detected (about a factor of three) in the 1-2keV flux, between the ASCA and a previous ROSAT observation. These characteristics clearly suggest an active galactic nucleus (AGN) origin for the X-ray emission. However, the precise nature of this AGN still remains uncertain. There is no evidence for a high absorbing column density above the Galactic value. Moreover, there is no strong evidence for an Fe line at 6.4keV, with the 90per cent upper limit on the equivalent width being 0.9keV. Thus the X-ray spectrum is consistent with an unobscured Seyfert 1 interpretation. This discrepancy with the optical spectrum, may be explained by either a strong star-forming component or a `dusty' ionized absorber. Finally, the possibility that IRAS00317-2142 may harbour a heavily obscured AGN where the X-ray emission is mainly owing to scattered light, appears less plausible because of the high value of the fxf[Oiii] ratio which is more indicative of an unobscured Seyfert 1 type AGN.
2000, Royal Astronomical Society