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The hardest X-ray source in the ASCA Large Sky Survey: Discovery of a new type 2 Seyfert

Masaaki Sakano·Katsuji Koyama·Takeshi Tsuru·Hisamitsu Awaki·Yoshihiro Ueda·Tadayuki Takahashi·Masayuki Akiyama·Kouji Ohta·Toru Yamada
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Abstract

We present results of ASCA deep exposure observations of the hardest X-ray source discovered in the ASCA Large Sky Survey (LSS) project, designated as AX J131501+3141. We extract its accurate X-ray spectrum, taking account of the contamination from a nearby soft source (AX J131502+3142), separated only by 1'. AX J131501+3141 exhibits a large absorption of NH = (6 +4 -2)x 10^22 H/cm^2 with a photon index Γ= 1.5 +0.7 -0.6. The 2--10 keV flux was about 5 x 10^-13 erg/s/cm^2 and was time variable by a factor of 30% in 0.5 year. From the highly absorbed X-ray spectrum and the time variability, as well as the results of the optical follow-up observations (Akiyama et al. 1998, astro-ph/9801173), we conclude that AX J131501+3141 is a type 2 Seyfert galaxy. Discovery of such a low flux and highly absorbed X-ray source could have a significant impact on the origin of the cosmic X-ray background.

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Masaaki Sakano, Katsuji Koyama, Takeshi Tsuru, Hisamitsu Awaki, Yoshihiro Ueda, Tadayuki Takahashi, Masayuki Akiyama, Kouji Ohta, Toru Yamada. 1998-04-13. The hardest X-ray source in the ASCA Large Sky Survey: Discovery of a new type 2 Seyfert. https://doi.org/10.1086/306158

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