ASCA Observations of Two Ultraluminous IRAS Galaxies: IRAS 15307+3252 and IRAS 20460+1925
Abstract
We report on ASCA observations of two ultraluminous far-infrared galaxies, IRAS 15307+3252 and IRAS 20460+1925. An X-ray flux of 1.53 times 10(-12) erg cm(-2) s(-1) in the 2--10 keV band was detected from IRAS 20460+1925. The continuous spectrum is well represented by a power law with a photon index of 1.99(+0.18}_{-0.15) and excess photoelectric absorption by a column of (2.6(+0.29}_{-0.32) )times 10(22) cm(-2) in the rest frame. The spectrum also shows an iron K emission line with an equivalent width of 260(+145}_{-137) eV and a centroid energy of 6.36+/- 0.08 keV in the rest frame. These spectral properties are consistent with those of Seyfert-2 galaxies, although the intrinsic 2--10 keV X-ray luminosity (corrected for absorption) of 1.20times 10(44) erg s(-1) is high and close to that of quasars. No X-rays were detected from IRAS 15307+3252, and the upper limit to the X-ray flux is 7.2 times 10(-14) erg cm(-2) s(-1) in the 2--10 keV band. However, the upper limit on the ratio of the X-ray flux to the far-infrared flux is not inconsistent with a source containing a highly obscured quasar.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- April 1997
- DOI:
- 10.1093/pasj/49.2.179
- Bibcode:
- 1997PASJ...49..179O
- Keywords:
-
- GALAXIES: INDIVIDUAL (IRAS 15307+3252;
- IRAS 20460+1925);
- GALAXIES: SEYFERT;
- GALAXIES: X-RAYS;
- QUASARS