A candidate active galactic nucleus with a pure soft thermal X-ray spectrum

Yuichi Terashima, Naoya Kamizasa, Hisamitsu Awaki, Aya Kubota, Yoshihiro Ueda

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

We report the discovery of a candidate active galactic nucleus (AGN), 2XMM J123103.2+110648 at z = 0.13, with an X-ray spectrum represented purely by soft thermal emission reminiscent of Galactic black hole (BH) binaries in the disk-dominated state. This object was found in the second XMM-Newton serendipitous source catalog as a highly variable X-ray source. In three separate observations, its X-ray spectrum can be represented either by a multicolor disk blackbody model with an inner temperature of kT in 0.16-0.21keV or a Wien spectrum Comptonized by an optically thick plasma with kT 0.14-0.18keV. The soft X-ray luminosity in the 0.5-2keV band is estimated to be (1.6-3.8) × 1042ergs-1. Hard emission above 2keV is not detected. The ratio of the soft to hard emission is the strongest among AGNs observed thus far. Spectra selected in high/low-flux time intervals are examined in order to study spectral variability. In the second observation with the highest signal-to-noise ratio, the low-energy (below 0.7keV) spectral regime flattens when the flux is high, while the shape of the high-energy part (1-1.7keV) remains unchanged. This behavior is qualitatively consistent with being caused by strong Comptonization. Both the strong soft excess and spectral change consistent with Comptonization in the X-ray spectrum imply that the Eddington ratio is large, which requires a small BH mass (smaller than 10 5 M).

Original languageEnglish
Article number154
JournalAstrophysical Journal
Volume752
Issue number2
DOIs
Publication statusPublished - 2012 Jun 20

Fingerprint

active galactic nuclei
x rays
thermal emission
XMM-Newton telescope
signal-to-noise ratio
newton
catalogs
energy
signal to noise ratios
luminosity
intervals
plasma
temperature

Keywords

  • galaxies: active
  • X-rays: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

A candidate active galactic nucleus with a pure soft thermal X-ray spectrum. / Terashima, Yuichi; Kamizasa, Naoya; Awaki, Hisamitsu; Kubota, Aya; Ueda, Yoshihiro.

In: Astrophysical Journal, Vol. 752, No. 2, 154, 20.06.2012.

Research output: Contribution to journalArticle

Terashima, Yuichi ; Kamizasa, Naoya ; Awaki, Hisamitsu ; Kubota, Aya ; Ueda, Yoshihiro. / A candidate active galactic nucleus with a pure soft thermal X-ray spectrum. In: Astrophysical Journal. 2012 ; Vol. 752, No. 2.
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