Suzaku observation of two ultraluminous X-ray sources in NGC 1313

Tsunefumi Mizuno, Ryohei Miyawaki, Ken Ebisawa, Aya Kubota, Masao Miyamoto, Lisa M. Winter, Yoshihiro Ueda, Naoki Isobe, Gulab C. Dewangan, Chris Done, Richard E. Griffiths, Yoshito Haba, Motohide Kokubun, Jun'ichi Kotoku, Kazuo Makishima, Kyoko Matsushita, Ricard F. Mushotzky, Masaaki Namiki, Robert Petre, Hiromitsu TakahashiToru Tamagawa, Yuichi Terashima

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Two ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313, named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the observation for a net exposure of 28 ks (but over a gross time span of 90 ks), both objects varied in intensity by about 50%. The 0.4-10 keV X-ray luminosities of X-1 and X-2 were measured as 2.5 × 1040 erg s-1 and 5.8 × 1039 erg s-1, respectively, with the former exhibiting the highest ever reported for this ULX. The spectrum of X-1 can be explained by the sum of a strong and variable power-law component with a high-energy cutoff, and a stable multicolor blackbody with an innermost disk temperature of ∼ 0.2 keV. These results suggest that X-1 was in a "very high" state, where disk emission is strongly Comptonized. The absorber within NGC 1313 toward X-1 is suggested to have a subsolar oxygen abundance. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor blackbody model with an innermost disk temperature of 1.2-1.3 keV, and becomes flatter as the source becomes brighter. Hence, X-2 is interpreted to be in a slim-disk state. These results suggest that the two ULXs have black hole masses of some dozens to a few hundred of solar masses.

Original languageEnglish
JournalPublications of the Astronomical Society of Japan
Volume59
Issue number1 SPEC. ISS.
Publication statusPublished - 2007
Externally publishedYes

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erg
x rays
absorbers
power law
cut-off
temperature
luminosity
galaxies
oxygen
energy
exposure

Keywords

  • Accretion, accretion disks
  • Black hole physics
  • X-rays: individual (NGC 1313 X-1, NGC 1313 X-2)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Mizuno, T., Miyawaki, R., Ebisawa, K., Kubota, A., Miyamoto, M., Winter, L. M., ... Terashima, Y. (2007). Suzaku observation of two ultraluminous X-ray sources in NGC 1313. Publications of the Astronomical Society of Japan, 59(1 SPEC. ISS.).

Suzaku observation of two ultraluminous X-ray sources in NGC 1313. / Mizuno, Tsunefumi; Miyawaki, Ryohei; Ebisawa, Ken; Kubota, Aya; Miyamoto, Masao; Winter, Lisa M.; Ueda, Yoshihiro; Isobe, Naoki; Dewangan, Gulab C.; Done, Chris; Griffiths, Richard E.; Haba, Yoshito; Kokubun, Motohide; Kotoku, Jun'ichi; Makishima, Kazuo; Matsushita, Kyoko; Mushotzky, Ricard F.; Namiki, Masaaki; Petre, Robert; Takahashi, Hiromitsu; Tamagawa, Toru; Terashima, Yuichi.

In: Publications of the Astronomical Society of Japan, Vol. 59, No. 1 SPEC. ISS., 2007.

Research output: Contribution to journalArticle

Mizuno, T, Miyawaki, R, Ebisawa, K, Kubota, A, Miyamoto, M, Winter, LM, Ueda, Y, Isobe, N, Dewangan, GC, Done, C, Griffiths, RE, Haba, Y, Kokubun, M, Kotoku, J, Makishima, K, Matsushita, K, Mushotzky, RF, Namiki, M, Petre, R, Takahashi, H, Tamagawa, T & Terashima, Y 2007, 'Suzaku observation of two ultraluminous X-ray sources in NGC 1313', Publications of the Astronomical Society of Japan, vol. 59, no. 1 SPEC. ISS..
Mizuno T, Miyawaki R, Ebisawa K, Kubota A, Miyamoto M, Winter LM et al. Suzaku observation of two ultraluminous X-ray sources in NGC 1313. Publications of the Astronomical Society of Japan. 2007;59(1 SPEC. ISS.).
Mizuno, Tsunefumi ; Miyawaki, Ryohei ; Ebisawa, Ken ; Kubota, Aya ; Miyamoto, Masao ; Winter, Lisa M. ; Ueda, Yoshihiro ; Isobe, Naoki ; Dewangan, Gulab C. ; Done, Chris ; Griffiths, Richard E. ; Haba, Yoshito ; Kokubun, Motohide ; Kotoku, Jun'ichi ; Makishima, Kazuo ; Matsushita, Kyoko ; Mushotzky, Ricard F. ; Namiki, Masaaki ; Petre, Robert ; Takahashi, Hiromitsu ; Tamagawa, Toru ; Terashima, Yuichi. / Suzaku observation of two ultraluminous X-ray sources in NGC 1313. In: Publications of the Astronomical Society of Japan. 2007 ; Vol. 59, No. 1 SPEC. ISS.
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abstract = "Two ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313, named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the observation for a net exposure of 28 ks (but over a gross time span of 90 ks), both objects varied in intensity by about 50{\%}. The 0.4-10 keV X-ray luminosities of X-1 and X-2 were measured as 2.5 × 1040 erg s-1 and 5.8 × 1039 erg s-1, respectively, with the former exhibiting the highest ever reported for this ULX. The spectrum of X-1 can be explained by the sum of a strong and variable power-law component with a high-energy cutoff, and a stable multicolor blackbody with an innermost disk temperature of ∼ 0.2 keV. These results suggest that X-1 was in a {"}very high{"} state, where disk emission is strongly Comptonized. The absorber within NGC 1313 toward X-1 is suggested to have a subsolar oxygen abundance. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor blackbody model with an innermost disk temperature of 1.2-1.3 keV, and becomes flatter as the source becomes brighter. Hence, X-2 is interpreted to be in a slim-disk state. These results suggest that the two ULXs have black hole masses of some dozens to a few hundred of solar masses.",
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T1 - Suzaku observation of two ultraluminous X-ray sources in NGC 1313

AU - Mizuno, Tsunefumi

AU - Miyawaki, Ryohei

AU - Ebisawa, Ken

AU - Kubota, Aya

AU - Miyamoto, Masao

AU - Winter, Lisa M.

AU - Ueda, Yoshihiro

AU - Isobe, Naoki

AU - Dewangan, Gulab C.

AU - Done, Chris

AU - Griffiths, Richard E.

AU - Haba, Yoshito

AU - Kokubun, Motohide

AU - Kotoku, Jun'ichi

AU - Makishima, Kazuo

AU - Matsushita, Kyoko

AU - Mushotzky, Ricard F.

AU - Namiki, Masaaki

AU - Petre, Robert

AU - Takahashi, Hiromitsu

AU - Tamagawa, Toru

AU - Terashima, Yuichi

PY - 2007

Y1 - 2007

N2 - Two ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313, named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the observation for a net exposure of 28 ks (but over a gross time span of 90 ks), both objects varied in intensity by about 50%. The 0.4-10 keV X-ray luminosities of X-1 and X-2 were measured as 2.5 × 1040 erg s-1 and 5.8 × 1039 erg s-1, respectively, with the former exhibiting the highest ever reported for this ULX. The spectrum of X-1 can be explained by the sum of a strong and variable power-law component with a high-energy cutoff, and a stable multicolor blackbody with an innermost disk temperature of ∼ 0.2 keV. These results suggest that X-1 was in a "very high" state, where disk emission is strongly Comptonized. The absorber within NGC 1313 toward X-1 is suggested to have a subsolar oxygen abundance. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor blackbody model with an innermost disk temperature of 1.2-1.3 keV, and becomes flatter as the source becomes brighter. Hence, X-2 is interpreted to be in a slim-disk state. These results suggest that the two ULXs have black hole masses of some dozens to a few hundred of solar masses.

AB - Two ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313, named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the observation for a net exposure of 28 ks (but over a gross time span of 90 ks), both objects varied in intensity by about 50%. The 0.4-10 keV X-ray luminosities of X-1 and X-2 were measured as 2.5 × 1040 erg s-1 and 5.8 × 1039 erg s-1, respectively, with the former exhibiting the highest ever reported for this ULX. The spectrum of X-1 can be explained by the sum of a strong and variable power-law component with a high-energy cutoff, and a stable multicolor blackbody with an innermost disk temperature of ∼ 0.2 keV. These results suggest that X-1 was in a "very high" state, where disk emission is strongly Comptonized. The absorber within NGC 1313 toward X-1 is suggested to have a subsolar oxygen abundance. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor blackbody model with an innermost disk temperature of 1.2-1.3 keV, and becomes flatter as the source becomes brighter. Hence, X-2 is interpreted to be in a slim-disk state. These results suggest that the two ULXs have black hole masses of some dozens to a few hundred of solar masses.

KW - Accretion, accretion disks

KW - Black hole physics

KW - X-rays: individual (NGC 1313 X-1, NGC 1313 X-2)

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