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

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


We present results of the 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 into account the contamination from a nearby soft source (AX J131502 + 3142) separated from it by only 1′. AX J131501 + 3141 exhibits a large absorption of NH = 6-2+4 × 1022 H cm-2, with a photon index Γ = 1.51-0.6+0.7. The 2-10 keV flux was about 5 × 10-13 ergs cm-2 s-1, and was time variable by a factor of 30% in 0.5 yr. From the highly absorbed X-ray spectrum and the time variability, as well as the results of the optical follow-up observations, 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 our understanding of the origin of the cosmic X-ray background.

Original languageEnglish
Pages (from-to)129-133
Number of pages5
JournalAstrophysical Journal
Issue number1 PART I
Publication statusPublished - 1998


  • Diffuse radiation
  • Galaxies: active
  • Galaxies: seyfert
  • X-rays: galaxies


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