Discovery of a bright transient ultraluminous X-ray source, Suzaku J1305-4931 in NGC 4945

Naoki Isobe, Aya Kubota, Kazuo Makishima, Poshak Gandhi, Richard E. Griffiths, Gulab C. Dewangan, Takeshi Itoh, Tsunefumi Mizuno

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

An X-ray source, Suzaku J1305-4931, was discovered in the south-west arm of a nearby Seyfert II galaxy, NGC 4945, at 0.5-10 keV flux of 2.2 × 10 -12 erg Cm-2 s-1 during a Suzaku observation conducted on 2006 January 15-17. It was undetectable in a shorter observation on 2005 August 22-23, with an upper limit of 1.7 × 10-14 erg cm-2 s-1. At a distance of 3.7 Mpc, the bolometric luminosity of the source became Lbol = 4.4 × 1039 α erg s-1, where α = (cos 60°/cos i) and i is the disk inclination. The time-averaged X-ray spectrum of the source is described by a multi-color disk model, with an innermost disk temperature of Tin = 1 .69-0.05+0.06 keV. It varied by a factor of 2 in intensity, following a clear correlation of Lbol ∝ T in4. The innermost disk radius is inferred to stay constant at Rin = 79-3.9+4.0α1/2 km, suggesting the presence of a standard accretion disk. Relating Rin with the last stable orbit around a non-rotating black hole yields a rather low black-hole mass, ∼ 9α1/2 solar masses, which would imply that the source is shining at a considerable super-Eddington luminosity. These results can be better interpreted by invoking sub-Eddington emission from a rapidly spinning black hole with 20-130 solar masses.

Original languageEnglish
JournalPublications of the Astronomical Society of Japan
Volume60
Issue numberSPEC. ISS. 1
Publication statusPublished - 2008

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erg
x rays
luminosity
tin
guy wires
accretion
accretion disks
metal spinning
inclination
galaxies
orbits
color
radii
temperature

Keywords

  • Accretion, accretion disks
  • Black hole physics
  • Galaxies: individual (NGC 4945)
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Isobe, N., Kubota, A., Makishima, K., Gandhi, P., Griffiths, R. E., Dewangan, G. C., ... Mizuno, T. (2008). Discovery of a bright transient ultraluminous X-ray source, Suzaku J1305-4931 in NGC 4945. Publications of the Astronomical Society of Japan, 60(SPEC. ISS. 1).

Discovery of a bright transient ultraluminous X-ray source, Suzaku J1305-4931 in NGC 4945. / Isobe, Naoki; Kubota, Aya; Makishima, Kazuo; Gandhi, Poshak; Griffiths, Richard E.; Dewangan, Gulab C.; Itoh, Takeshi; Mizuno, Tsunefumi.

In: Publications of the Astronomical Society of Japan, Vol. 60, No. SPEC. ISS. 1, 2008.

Research output: Contribution to journalArticle

Isobe, N, Kubota, A, Makishima, K, Gandhi, P, Griffiths, RE, Dewangan, GC, Itoh, T & Mizuno, T 2008, 'Discovery of a bright transient ultraluminous X-ray source, Suzaku J1305-4931 in NGC 4945', Publications of the Astronomical Society of Japan, vol. 60, no. SPEC. ISS. 1.
Isobe, Naoki ; Kubota, Aya ; Makishima, Kazuo ; Gandhi, Poshak ; Griffiths, Richard E. ; Dewangan, Gulab C. ; Itoh, Takeshi ; Mizuno, Tsunefumi. / Discovery of a bright transient ultraluminous X-ray source, Suzaku J1305-4931 in NGC 4945. In: Publications of the Astronomical Society of Japan. 2008 ; Vol. 60, No. SPEC. ISS. 1.
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AU - Isobe, Naoki

AU - Kubota, Aya

AU - Makishima, Kazuo

AU - Gandhi, Poshak

AU - Griffiths, Richard E.

AU - Dewangan, Gulab C.

AU - Itoh, Takeshi

AU - Mizuno, Tsunefumi

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N2 - An X-ray source, Suzaku J1305-4931, was discovered in the south-west arm of a nearby Seyfert II galaxy, NGC 4945, at 0.5-10 keV flux of 2.2 × 10 -12 erg Cm-2 s-1 during a Suzaku observation conducted on 2006 January 15-17. It was undetectable in a shorter observation on 2005 August 22-23, with an upper limit of 1.7 × 10-14 erg cm-2 s-1. At a distance of 3.7 Mpc, the bolometric luminosity of the source became Lbol = 4.4 × 1039 α erg s-1, where α = (cos 60°/cos i) and i is the disk inclination. The time-averaged X-ray spectrum of the source is described by a multi-color disk model, with an innermost disk temperature of Tin = 1 .69-0.05+0.06 keV. It varied by a factor of 2 in intensity, following a clear correlation of Lbol ∝ T in4. The innermost disk radius is inferred to stay constant at Rin = 79-3.9+4.0α1/2 km, suggesting the presence of a standard accretion disk. Relating Rin with the last stable orbit around a non-rotating black hole yields a rather low black-hole mass, ∼ 9α1/2 solar masses, which would imply that the source is shining at a considerable super-Eddington luminosity. These results can be better interpreted by invoking sub-Eddington emission from a rapidly spinning black hole with 20-130 solar masses.

AB - An X-ray source, Suzaku J1305-4931, was discovered in the south-west arm of a nearby Seyfert II galaxy, NGC 4945, at 0.5-10 keV flux of 2.2 × 10 -12 erg Cm-2 s-1 during a Suzaku observation conducted on 2006 January 15-17. It was undetectable in a shorter observation on 2005 August 22-23, with an upper limit of 1.7 × 10-14 erg cm-2 s-1. At a distance of 3.7 Mpc, the bolometric luminosity of the source became Lbol = 4.4 × 1039 α erg s-1, where α = (cos 60°/cos i) and i is the disk inclination. The time-averaged X-ray spectrum of the source is described by a multi-color disk model, with an innermost disk temperature of Tin = 1 .69-0.05+0.06 keV. It varied by a factor of 2 in intensity, following a clear correlation of Lbol ∝ T in4. The innermost disk radius is inferred to stay constant at Rin = 79-3.9+4.0α1/2 km, suggesting the presence of a standard accretion disk. Relating Rin with the last stable orbit around a non-rotating black hole yields a rather low black-hole mass, ∼ 9α1/2 solar masses, which would imply that the source is shining at a considerable super-Eddington luminosity. These results can be better interpreted by invoking sub-Eddington emission from a rapidly spinning black hole with 20-130 solar masses.

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KW - X-rays: galaxies

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