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Title:
ASCA Observations of Two Ultraluminous IRAS Galaxies: IRAS 15307+3252 and IRAS 20460+1925
Authors:
Ogasaka, Yasushi; Inoue, Hajime; Brandt, William N.; Fabian, Andrew C.; Kii, Tsuneo; Nakagawa, Takao; Fujimoto, Ryuichi; Otani, Chiko
Affiliation:
AA(The Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229; Present address: NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, U.S.A.; E-mail(YO): ), AB(The Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229), AC(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, U.K.; Present address: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, U.S.A.), AD(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, U.K.), AE(The Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229), AF(The Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229), AG(The Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229), AH(The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-01)
Publication:
Publ. of the Astronomical Society of Japan, v.49, p.179-185. (PASJ Homepage)
Publication Date:
04/1997
Origin:
PASJ
PASJ Keywords:
GALAXIES: INDIVIDUAL (IRAS 15307+3252, IRAS 20460+1925), GALAXIES: SEYFERT, GALAXIES: X-RAYS, QUASARS
Bibliographic Code:
1997PASJ...49..179O

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.

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