Nature of the soft ULX in NGC 247

Super-Eddington outflow and transition between the supersoft and soft ultraluminous regimes

Hua Feng, Lian Tao, Philip Kaaret, Fabien Grise

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

We report on XMM-Newton/Chandra/Swift/Hubble Space Telescope observations of the ultraluminous X-ray source (ULX) in NGC 247, which is found to make transitions between the supersoft ultraluminous (SSUL) regime with a spectrum dominated by a cool (∼0.1 keV) blackbody component and the soft ultraluminous (SUL) regime with comparable luminosities shared by the blackbody and power-law components. Multi-epoch observations revealed an anti-correlation between the blackbody radius and temperature, Rbb ∝ Tbb -2.8±0.3, ruling out a standard accretion disk as the origin of the soft X-ray emission. The soft X-ray emission is much more variable on both short and long timescales in the SSUL regime than in the SUL regime. We suggest that the SSUL regime may be an extension of the ultraluminous state toward the high accretion end, being an extreme case of the SUL regime, with the blackbody emission arising from the photosphere of thick outflows and the hard X-rays being emission leaked from the embedded accretion disk via the central low-density funnel or advected through the wind. However, the scenario that the supersoft ULXs are standard ULXs viewed nearly edge-on cannot be ruled out. Flux dips on a timescale of 200 s were observed. The dips cannot be explained by an increase of absorption, but could be due to the change of accretion rate or related to thermal fluctuations in the wind or disk. The optical emission of NGC 247 ULX exhibits a blackbody spectrum at a temperature of 19,000 K with a radius of 20 , likely arising from an OB supergiant companion star.

Original languageEnglish (US)
Article number117
JournalAstrophysical Journal
Volume831
Issue number2
DOIs
StatePublished - Nov 10 2016

Fingerprint

outflow
accretion
x rays
accretion disks
dip
supergiant stars
timescale
companion stars
funnels
radii
photosphere
XMM-Newton telescope
Hubble Space Telescope
newton
light emission
power law
temperature
luminosity
time measurement

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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title = "Nature of the soft ULX in NGC 247: Super-Eddington outflow and transition between the supersoft and soft ultraluminous regimes",
abstract = "We report on XMM-Newton/Chandra/Swift/Hubble Space Telescope observations of the ultraluminous X-ray source (ULX) in NGC 247, which is found to make transitions between the supersoft ultraluminous (SSUL) regime with a spectrum dominated by a cool (∼0.1 keV) blackbody component and the soft ultraluminous (SUL) regime with comparable luminosities shared by the blackbody and power-law components. Multi-epoch observations revealed an anti-correlation between the blackbody radius and temperature, Rbb ∝ Tbb -2.8±0.3, ruling out a standard accretion disk as the origin of the soft X-ray emission. The soft X-ray emission is much more variable on both short and long timescales in the SSUL regime than in the SUL regime. We suggest that the SSUL regime may be an extension of the ultraluminous state toward the high accretion end, being an extreme case of the SUL regime, with the blackbody emission arising from the photosphere of thick outflows and the hard X-rays being emission leaked from the embedded accretion disk via the central low-density funnel or advected through the wind. However, the scenario that the supersoft ULXs are standard ULXs viewed nearly edge-on cannot be ruled out. Flux dips on a timescale of 200 s were observed. The dips cannot be explained by an increase of absorption, but could be due to the change of accretion rate or related to thermal fluctuations in the wind or disk. The optical emission of NGC 247 ULX exhibits a blackbody spectrum at a temperature of 19,000 K with a radius of 20 , likely arising from an OB supergiant companion star.",
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Nature of the soft ULX in NGC 247 : Super-Eddington outflow and transition between the supersoft and soft ultraluminous regimes. / Feng, Hua; Tao, Lian; Kaaret, Philip; Grise, Fabien.

In: Astrophysical Journal, Vol. 831, No. 2, 117, 10.11.2016.

Research output: Contribution to journalArticle

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AU - Feng, Hua

AU - Tao, Lian

AU - Kaaret, Philip

AU - Grise, Fabien

PY - 2016/11/10

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