NGC 7582: The prototype narrow-line X-ray galaxy

NGC 7582 is a candidate prototype of the narrow line X-ray galaxies (NLXGs) found in deep X-ray surveys. An ASCA observation shows the hard (>3 keV) X -ray continuum of NGC 7582 drops 40% in similar to 6 ks, implying an active galactic nucleus (AGN), while the soft band (<3 keV) does not drop in conc ert with the hard continuum, requiring a separate component. The X-ray spec trum of NGC 7582 also shows a clear 0.5-2 keV soft (kT = 0.8(-0.3)(+0.9) ke V or Gamma = 2.4 +/- 0.6; L-x = 6 x 10(40) ergs s(-1)) low-energy component , in addition to a heavily absorbed [N-H = (6 +/- 2) x 10(22) cm(-2)] and v ariable 2-10 keV power law [Gamma = 0.7(-0.4)(+0.3); L-x = (1.7-2.3) x 10(4 2) ergs s(-1)]. This is one of the flattest 2-10 keV slopes in any AGN obse rved with ASCA. (The ROSAT HRI image of NGC 7582 further suggests extent to the SE.) These observations make it clear that the hard X-ray emission of NGC 7582, the most "narrow-line" of the NLXGs, is associated with an AGN. T he strong suggestion is that all NLXGs are obscured AGNs, as hypothesized t o explain the X-ray background spectral paradox. The separate soft X-ray co mponent makes NGC 7582 land by extension other NLXGs) detectable as a ROSAT source.