Another interpretation of the power-law-type spectrum of an ultraluminous compact X-ray source in IC 342

Kubota, Aya; Done, Chris; Makishima, Kazuo

doi:10.1046/j.1365-8711.2002.06043.x

Cited by 52 publications

(71 citation statements)

References 41 publications

(63 reference statements)

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“…This is equivalent to saying that the radius of the emitting region is not constant between sources or for the same source at various epochs. A constant inner-disk radius Rin ≈ 1.19rin ≈ RISCO (radius of the innermost stable circular orbit) is usually taken as the defining property of the high/soft they are more likely to be high-inclination objects, as discussed in Section 5.3. state in luminous BHs at accretion rates a few percent of the Eddington limit (Kubota, Done & Makishima 2002;Remillard & McClintock 2006). The IMBH scenario was based on the interpretation of the thermal component as disk emission in the high/soft state; however, we see that the thermal component in ULSs does not behave like a standard disk in the canonical high/soft state.…”

Section: X-ray Spectral Propertiesmentioning

confidence: 76%

Optically thick outflows in ultraluminous supersoft sources

Urquhart¹,

Soria²

2015

Mon. Not. R. Astron. Soc.

107

181

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Ultraluminous supersoft sources (ULSs) are defined by a thermal spectrum with colour temperatures ∼0.1 keV, bolometric luminosities ∼ a few 10 39 erg s −1 , and almost no emission above 1 keV. It has never been clear how they fit into the general scheme of accreting compact objects. To address this problem, we studied a sample of seven ULSs with extensive Chandra and XMM-Newton coverage. We find an anticorrelation between fitted temperatures and radii of the thermal emitter, and no correlation between bolometric luminosity and radius or temperature. We compare the physical parameters of ULSs with those of classical supersoft sources, thought to be surfacenuclear-burning white dwarfs, and of ultraluminous X-ray sources (ULXs), thought to be super-Eddington stellar-mass black holes. We argue that ULSs are the sub-class of ULXs seen through the densest wind, perhaps an extension of the soft-ultraluminous regime. We suggest that in ULSs, the massive disk outflow becomes effectively optically thick and forms a large photosphere, shrouding the inner regions from our view. Our model predicts that when the photosphere expands to 10 5 km and the temperature decreases below ≈50 eV, ULSs become brighter in the far-UV but undetectable in X-rays. Conversely, we find that harder emission components begin to appear in ULSs when the fitted size of the thermal emitter is smallest (interpreted as a shrinking of the photosphere). The observed short-term variability and absorption edges are also consistent with clumpy outflows. We suggest that the transition between ULXs (with a harder tail) and ULSs (with only a soft thermal component) occurs at blackbody temperatures of ≈150 eV.

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Section: X-ray Spectral Propertiesmentioning

confidence: 76%

Optically thick outflows in ultraluminous supersoft sources

Urquhart¹,

Soria²

2015

Mon. Not. R. Astron. Soc.

107

181

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“…Another possibility is that X-11, X-16, and X-37 are stellarmass black holes in the ''very high'' state (see the reviews mentioned previously; see also Kubota et al 2002). Certainly, if ULXs behave similarly to Galactic stellar-mass black holes, it is reasonable to expect that this state holds at the luminosities observed.…”

Section: Discussionmentioning

confidence: 96%

XMM‐NewtonSpectroscopy of Four Bright Ultraluminous X‐Ray Sources in the Antennae Galaxies (NGC 4038/4039)

Miller

Zezas

Fabbiano

et al. 2004

ApJ

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We report the results of spectral fits to four bright ultraluminous X-ray sources ( ULXs) in the Antennae galaxies ( NGC 4038/4039) observed for 41 ks with XMM-Newton. Although emission regions are not resolved as well as in prior Chandra observations, at least four ULXs ( X-11, X-16, X-37, and X-44 in the Zezas and Fabbiano scheme) are sufficiently bright and well separated with XMM-Newton that reliable extractions and spectral analyses are possible. We find that the single-component multicolor disk blackbody models cannot describe any of the spectra. Sources X-11 and X-16 are acceptably fitted with simple power-law models. A thermal bremsstrahlung model provides a better fit to the spectrum of X-44. Including a disk blackbody component to the spectrum of X-37 improves the fit and reveals an apparently cool disk (kT ¼ 0:13 AE 0:02 keV ). This would suggest a parallel to cool disks recently found in other very luminous ULXs, which may contain intermediate-mass black holes; however, the complex diffuse emission of the Antennae demands that this finding be regarded cautiously.

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“…Such strong Comptonization is believed to occur in Galactic jet sources (e.g., GRO J1655À40, Kubota, Makishima, & Ebisawa 2001b) and possibly in an ULX in IC 342 (Kubota et al 2002). Kubota et al (2002) reanalyzed the ASCA spectrum of source 1 in IC 342 observed in 2000. The spectrum can be fitted with either a power law (À ¼ 1:73 AE 0:06, modified by an ionized Fe K edge at 8:4 AE 0:3 keV) or a Comptonized blackbody with an inner disk temperature of kT in ¼ 1:1 AE 0:3 keV.…”

Section: Ulxs With a Power-law Spectrummentioning

confidence: 99%

The Luminous X‐Ray Source Population in M51 Observed withChandra

Terashima

Wilson

2004

ApJ

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We present the results of two Chandra observations (separated by 1 yr) of the population of X-ray sources in the spiral galaxy M51 (NGC 5194 and NGC 5195). One hundred and thirteen X-ray sources have been detected in an 8A4 Â 8A4 (20:4 Â 20:4 kpc) region, and 84 and 12 of them project within the disks of NGC 5194 and NGC 5195, respectively. Nine and 28 sources have luminosities exceeding 1 Â 10 39 ergs s À1 (ultraluminous X-ray sources or ULXs) and 1 Â 10 38 ergs s À1 in the 0.5-8 keV band, respectively, assuming that they are associated with M51. The number of ULXs is much higher than found in most normal spiral and elliptical galaxies. Most of the X-ray sources and all seven of the ULXs in NGC 5194 are located in, or close to, a spiral arm, suggesting a connection with recent star formation. The cumulative luminosity function of the X-ray sources in NGC 5194 with Lð0:5 8 keVÞ > 10 38 ergs s À1 is well described by a power law, N ½>L(0.5-8 keVÞ / L(0.5-8 keV) À with ¼ 0:91. The X-ray spectra of most of the detected sources are consistent with a power law with a photon index between 1 and 2, with a few sources showing harder or softer spectra. The spectra of most ULXs are consistent with both a power law and a multicolor disk blackbody (MCD) model, while a power-law model is preferable to an MCD model in two ULXs. One ULX (NGC 5194 source 69) shows drastic spectral steepening accompanied by a decline in luminosity by a factor of 3460 in the 2-10 keV band between the two observations. This source also exhibited a possible period of 2.1 hr in the 2000 observation. Another ULX (NGC 5194 source 26) shows strong emission lines from highly ionized species. The masses of the compact objects and mass accretion rates in ULXs and other X-ray sources are not well constrained by these observations. If we adopt an MCD interpretation, their MCD parameters imply that most of the X-ray sources are stellar mass ($5-10 M ) black holes accreting near or above the Eddington rate, although other possibilities (intermediate-mass black holes and relativistically beamed emission) cannot be excluded. The power-law sources may instead represent Comptonized disk or nonthermal emission. Two ULXs have very soft spectra; MCD models require kT % 0:1 keV. We discuss the possibility that this soft emission originates in an accretion disk around an intermediate-mass black hole. We also present a study of the nucleus of, and discrete sources (including two ULXs) in, the companion galaxy NGC 5195.

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Another interpretation of the power-law-type spectrum of an ultraluminous compact X-ray source in IC 342

Cited by 52 publications

References 41 publications

Optically thick outflows in ultraluminous supersoft sources

Optically thick outflows in ultraluminous supersoft sources

XMM‐NewtonSpectroscopy of Four Bright Ultraluminous X‐Ray Sources in the Antennae Galaxies (NGC 4038/4039)

The Luminous X‐Ray Source Population in M51 Observed withChandra

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