<i>XMM</i>‐<i>Newton</i>Observations of Ultraluminous X‐Ray Sources in Nearby Galaxies

Feng, Hua; Kaaret, Philip

doi:10.1086/491597

Cited by 81 publications

(108 citation statements)

References 38 publications

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“…McClintock & Remillard Furthermore, the IMBH model is not the only model that fits ULX spectra. Several sources have been identified in which a variant of this model, where the disc component fits to the hard end of the spectrum, provides a far superior fit (Stobbart, Roberts & Warwick 2004;Foschini et al 2004;Feng & Kaaret 2005). As discussed by Roberts et al (2005) this variant of the empirical black hole spectrum model does not provide a physical model for the X-ray emission -for example there cannot be sufficient photons present in the vicinity of the black hole to produce the dominant soft power-law through Compton up-scattering.…”

Section: The Imbh Model and Other Solutionsmentioning

confidence: 99%

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X-ray observations of ultraluminous X-ray sources

Roberts

2007

Astrophys Space Sci

177

187

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Ultraluminous X-ray sources (ULXs) are amongst the most intriguing of X-ray source classes. Their extreme luminosities -greater than 10 39 erg s −1 in the 0.3 -10 keV band alone -suggest either the presence of black holes larger than those regularly encountered in our own Galaxy (the Galactic centre excepted), or sources apparently radiating well above the Eddington limit. We review the insights afforded us by studies of their X-ray emission, focussing on what this reveals about the underlying compact object. In particular, we discuss recent deep observations of ULXs by the XMMNewton observatory, and how the unprecedented data quality provided by this mission is starting to discriminate between the different physical models for these extraordinary X-ray emitters.

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Section: The Imbh Model and Other Solutionsmentioning

confidence: 99%

“…Unfortunately, ULXs do not generally show much short-term variability (Swartz et al 2004), with very few examples displaying sufficient variability power to establish a PSD from (Feng & Kaaret 2005). However, some measurements have been made.…”

Section: Power Spectral Densities For Ulxsmentioning

confidence: 99%

X-ray observations of ultraluminous X-ray sources

Roberts

2007

Astrophys Space Sci

177

187

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“…Both sources exhibit disk emission with temperatures lower than those found in stellar-mass black holes (Miller et al 2003), suggesting they could be IMBHs. In the luminosity versus temperature (L-kT) diagram of bright ULXs in nearby galaxies (Feng & Kaaret 2005), they appear in the low-temperature, high-luminosity class, which contains sources most likely to be IMBH candidates. Ramsey et al (2006) find a unique optical counterpart to X-2 in Hubble Space Telescope images and suggest that the companion star is a B1-B2 giant.…”

Section: Fabbiano and White 2006) Many Ulxs Show Strong Variabilitymentioning

confidence: 99%

Spectral State Transitions of the Ultraluminous X-Ray Sources X-1 and X-2 in NGC 1313

Feng

Kaaret

2006

ApJ

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X-ray spectral state transitions are a key signature of black hole X-ray binaries and follow a well-defined pattern. We examined 12 XMM-Newton observations of the nearby spiral galaxy NGC 1313, which harbors two compact ultraluminous X-ray sources (ULXs), X-1 and X-2, in order to determine if the state transitions in ULXs follow the same pattern. For both sources, the spectra were adequately fitted by an absorbed power law with the addition of a low-temperature ( keV) disk blackbody component required in six of the 12 obserkT p 0.1-0.3 vations. As the X-ray luminosity of X-1 increases to a maximum at ergs s Ϫ1 , the power-law photon 40 3 # 10 index softens to 2.5-3.0. This behavior is similar to the canonical spectral state transitions in Galactic black hole binaries, but the source never enters the high/soft or thermal-dominant state and instead enters the steep powerlaw state at high luminosities. X-2 has the opposite behavior and appears to be in the hard state, with a photon index of at high luminosity, but can soften to at the lower luminosities. G p 1.7-2.0 G p 2.5

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“…Transitions between two spectral states, similar to those seen in Galactic black hole systems, have been reported in NGC 1313 X-1 (Colbert & Mushotzky 1999) and two sources in IC 342 . Spectral transitions have also been reported in two sources in NGC 1313 (Feng & Kaaret 2006).…”

Section: Introductionmentioning

confidence: 65%

“…The large collecting area of XMM-Newton allows for detailed spectral fits to ULXs, which are often comprised of two components (Wang et al 2004;Feng & Kaaret 2005). However, Gonçalves & Soria (2006) have argued that such soft spectral components depend on the complexity of the fitting model.…”

Section: Introductionmentioning

confidence: 99%

The Dependence of the Estimated Luminosities of Ultraluminous X‐Ray Sources on Spectral Models

Devi

Misra

Agrawal

et al. 2007

ApJ

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Data from Chandra observations of 30 nearby galaxies were analyzed and 365 X-ray point sources were chosen whose spectra were not contaminated by excessive diffuse emission and not affected by photon pileup. The spectra of these sources were fitted using two spectral models (an absorbed power-law and a disk blackbody) to ascertain the dependence of estimated parameters on the spectral model used. It was found that the cumulative luminosity function depends on the choice of the spectral model, especially for luminosities >10 40 ergs s À1 . A large number ($80) of the sources have luminosities >10 39 ergs s À1 (ultraluminous X-ray sources) with indistinguishable average spectral parameters (inner disk temperature $1 keV and/or photon index À $ 2) with those of the lower luminosity ones. We identify four sources whose minimum luminosity exceeds 10 40 ergs s À1 . Their spectra are in general better represented by the disk blackbody model than the power-law one. These extremely luminous X-ray sources ( ELXs) can be grouped into two distinct spectral classes. Two of them have an inner disk temperature of <0.5 keV (supersoft), while the other two have temperatures k1.3 keV ( hard). The estimated inner disk temperatures of the supersoft ELXs are compatible with the hypothesis that they harbor intermediate-size black holes, which are accreting at $0.5 times their Eddington luminosity. The radiative mechanism for hard ELXs seems to be inverse Comptonization, which in contrast to standard black holes systems is probably saturated.

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XMM‐NewtonObservations of Ultraluminous X‐Ray Sources in Nearby Galaxies

Cited by 81 publications

References 38 publications

X-ray observations of ultraluminous X-ray sources

X-ray observations of ultraluminous X-ray sources

Spectral State Transitions of the Ultraluminous X-Ray Sources X-1 and X-2 in NGC 1313

The Dependence of the Estimated Luminosities of Ultraluminous X‐Ray Sources on Spectral Models

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