X-Ray and Optical Spectroscopy of IRAS 20181-2244: Not a Type 2 QSO, but a I ZW 1 Object

Details X-Ray and Optical Spectroscopy of IRAS 20181-2244: Not a Type 2 QSO, but a I ZW 1 Object X-Ray and Optical Spectroscopy of IRAS 20181-2244: Not a Type 2 QSO, but a I ZW 1 Object

Feb 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...494..194h&link_type=abstract

Astrophysical Journal v.494, p.194

Astronomy and Astrophysics

Astronomy

17

Galaxies: Active, Galaxies: Individual Alphanumeric: Iras 20181-2244, Galaxies: Seyfert, X-Rays: Galaxies, Infrared: Galaxies

Scientific paper

We analyze new optical spectra of IRAS 20181-2244 that confirm its classification as a I Zw 1 object (or narrow-line Seyfert 1 galaxy), one of 20 such objects detected in the ROSAT/IRAS all-sky survey. ASCA X-ray data on IRAS 20181-2244 support this classification since they are fitted by a simple power-law spectrum of Gamma = 2.37 +/- 0.09 that is typical of this class but steeper than that of ordinary Seyfert 1 or Seyfert 2 galaxies. Rapid X-ray variability is also observed in IRAS 20181-2244, ruling out a hidden/scattered QSO interpretation for this object. Its 0.5-10 keV luminosity is 5.5 x 1044 ergs s-1, and its variability signifies an efficiency of at least 4% for conversion of gravitational energy to X-rays. We discuss the important differences between the I Zw 1 class and the "type 2 QSO," or high-luminosity Seyfert 2 galaxy. While I Zw 1 objects of QSO-like luminosity are ubiquitous in infrared, optical, and soft X-ray selected samples, type 2 QSOs are rare, and there is a dearth of evidence for even a single one in X-rays. It is not clear how this imbalance relates to unified models of AGNs.

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