Radio Emission from an Ultraluminous X-ray Source

Kaaret, Philip; Corbel, S.; Prestwich, Andrea; Zezas, A.

doi:10.1126/science.1079610

Cited by 169 publications

(232 citation statements)

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“…Background estimates were extracted from regions of the same size nearby on the CCD. Previous observations of NGC 5408 X-1 suggest that the spectrum does not change dramatically (Kaaret et al 2003;Strohmayer et al 2007;Strohmayer & Mushotzky 2009), so we combined all observations into a single, average spectrum in order to obtain an average count rate to flux conversion. We fit the resulting spectrum with the sum of a power-law and disk blackbody (model diskpn in XSPEC), and fixed the absorbing column at the value measured previously (Strohmayer et al 2007).…”

Section: Data Extraction and Analysismentioning

confidence: 99%

Discovery of a 115 Day Orbital Period in the Ultraluminous X-Ray Source NGC 5408 X-1

Strohmayer¹

2009

ApJ

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We report the detection of a 115 day periodicity in Swift/X-Ray Telescope monitoring data from the ultraluminous X-ray source (ULX) NGC 5408 X-1. Our ongoing campaign samples its X-ray flux approximately twice weekly and has now achieved a temporal baseline of ≈ 485 days. Periodogram analysis reveals a significant periodicity with a period of 115.5 ± 4 days. The modulation is detected with a significance of 3.2 × 10 −4 . The fractional modulation amplitude decreases with increasing energy, ranging from 0.13 ± 0.02 above 1 keV to 0.24 ± 0.02 below 1 keV. The shape of the profile evolves as well, becoming less sharply peaked at higher energies. The periodogram analysis is consistent with a periodic process, however, continued monitoring is required to confirm the coherent nature of the modulation. Spectral analysis indicates that NGC 5408 X-1 can reach 0.3-10 keV luminosities of ≈ 2×10 40 erg s −1 . We suggest that, like the 62 day period of the ULX in M82 (X41.4+60), the periodicity detected in NGC 5408 X-1 represents the orbital period of the black hole binary containing the ULX. If this is true then the secondary can only be a giant or supergiant star.

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Section: Data Extraction and Analysismentioning

confidence: 99%

Discovery of a 115 Day Orbital Period in the Ultraluminous X-Ray Source NGC 5408 X-1

Strohmayer¹

2009

ApJ

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“…Their X-ray luminosities (Colbert & Mushotzky 1999;Kaaret et al 2001), thermal disk emissions (Kaaret et al 2003), variation timescales (Strohmayer & Mushotzky 2003;Dewangan et al 2006), and surrounding emission-line nebulae (Pakull & Mirioni 2003;Kaaret et al 2004b) suggest that they might have masses of 20-10 3 , falling into the class of intermediate-mass black M , holes (IMBHs). However, if the emission is beamed (King et al 2001;Körding et al 2002) or exceeds the Eddington limit (Begelman 2002;Ebisawa et al 2003), some or all ULXs may be stellar-mass black holes.…”

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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“…Other evidence that may suggest the presence of an IMBH includes observations of millihertz QPOs (Strohmayer & Mushotzky 2003), ionization nebulae ( Pakull & Mirioni 2003), and inferences of cool inner accretion disk temperatures (Kaaret et al 2003;Miller et al 2003Miller et al , 2004Cropper et al 2004; but see Feng & Kaaret 2007). Despite the several pieces of evidence supporting IMBH binaries as the model for ULXs, one of the main problems with this scenario lies in the unknown formation mechanism for such binaries.…”

Section: Introductionmentioning

confidence: 99%

“…Mucciarelli et al (2005;2007) found two candidate optical counterparts to the ULX NGC 1313 X-2 and reported the more likely candidate to be a B0YO9 main-sequence star. Finally, Kaaret et al (2003) and Copperwheat et al (2007) had tentatively identified a possible counterpart to the ULX in NGC 5408. Recently, Lang et al (2007) uniquely identified the counterpart to this ULX, based on a radio detection; it turns out to be the same star as the one previous studies had identified as most likely.…”

Section: Introductionmentioning

confidence: 99%

Models for the Observable System Parameters of Ultraluminous X‐Ray Sources

Madhusudhan

Rappaport

Podsiadlowski

et al. 2008

Astrophysical Journal

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We investigate the evolution of model populations of ultraluminous X-ray sources (ULXs), consisting of a black hole accretor in a binary with a donor star. Two of the models we consider invoke stellar-mass (up to $25 M ) black hole binaries (LMBHs), generated with a binary population synthesis code, while a third model uses intermediatemass ($1000 M ) black hole accretors ( IMBHs). For each model, we computed 30,000 binary evolution sequences. A scheme for calculating the optical flux from ULXs is discussed. We present ''probability images'' for the colormagnitude diagrams (CMDs) and for the orbital periodYX-ray luminosity (P orb -L x ) plane. We show how a population of luminous X-ray sources in a cluster of stars evolves with time. The most probable ULX system parameters correspond to high-mass donors (of initial mass k25 M ) with effective O through late B spectral types, and P orb between 1 and 10 days. Estimates of the numbers of ULXs in a typical galaxy as a function of L x are also presented. We find that if LMBHs are allowed to have super-Eddington L x , the binding energy parameter for the stellar envelope of the black hole progenitor must be k P 0:03 in order not to overproduce ULXs. Comparison of six known ULX counterparts with our model CMDs indicates that the IMBH model somewhat more closely matches the observations. We find that a significant contribution to the optical flux from the IMBH systems comes from intrinsic accretion disk radiation. In effect, IMBH systems, when operating at their maximum luminosities (10 41 Y10 42 ergs s À1 ), are milli-AGNs. While models of IMBH systems during the X-ray phase are attractive, their formation mechanism remains uncertain.

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Radio Emission from an Ultraluminous X-ray Source

Cited by 169 publications

References 38 publications

Discovery of a 115 Day Orbital Period in the Ultraluminous X-Ray Source NGC 5408 X-1

Discovery of a 115 Day Orbital Period in the Ultraluminous X-Ray Source NGC 5408 X-1

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

Models for the Observable System Parameters of Ultraluminous X‐Ray Sources

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