Observations of variable X-ray sources in globular clusters

Clark, G. W.; Markert, T. H.; Li, F. K.

doi:10.1086/181856

Cited by 55 publications

(22 citation statements)

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“…M 15 is known to host two strong X-ray sources, AC211 (Giacconi et al 1974;Clark et al 1975) and M 15 X2 (White & Angelini 2001), close to the core of the cluster. Both have been classified as low mass XRBs.…”

Section: Mass Limits From X-ray Observationsmentioning

confidence: 99%

No evidence for a central IMBH in M 15

Kirsten

Vlemmings

2012

A&A

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Intermediate mass black holes (IMBHs) with expected masses M • ≈ 10 4 M are thought to bridge the gap between stellar mass black holes (M • ≈ 3−100 M ) and supermassive black holes found at the centre of galaxies (M • > 10 6 M ). Until today, no IMBH has been confirmed observationally. The most promising objects to host an IMBH as their central mass are globular clusters. Here, we present high sensitivity multi-epoch 1.6 GHz very long baseline interferometry observations of the globular cluster M 15 that has been suggested to host an IMBH. Assuming the IMBH to be accreting matter from its surrounding we expect to detect it as a point source moving with the global motion of the cluster. However, we do not detect any such object within a radius of 6000 AU of the cluster centre in any of the five observations spread over more than one year. This rules out any variability of the putative IMBH on the time scale of one to two months. To get the most stringent upper limit for the flux density of the putative IMBH we concatenate the data of all five epochs. In this data we measure a 3σ upper flux limit of 10 μJy for a central source. We employ the fundamental plane of black hole activity to estimate the mass of the central IMBH candidate. Based on previous X-ray observations of M 15 our measurements indicate a 3σ upper mass limit of ≈500 M .

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Section: Mass Limits From X-ray Observationsmentioning

confidence: 99%

No evidence for a central IMBH in M 15

Kirsten

Vlemmings

2012

A&A

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“…The steady X-ray source 0512-401, located in the globular cluster NGC 1851 (Clark et aL 1975;Jeruigan and Clark, 1979;Hertz and Grindlay 1983), has been detected in most X-ray surveys, with an average flux of 1.6 • 10 -1~ erg cm -2 s -1 [range (< 1.0-4.5) • 10 -1~ erg cm -2 s-l]. Variability occurs on a time scale of days; during time scales of the order of hours the source does not vary much (Leahy et aL 1983;Ercan et al 1988;Parmar et aI.…”

Section: -401/ngc 1851mentioning

confidence: 99%

X-ray bursts

1993

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“…The number density of X-ray sources in globular clusters with luminosities greater than L X = 10 36 erg s −1 is 100-1000 times higher than that of the Galactic disk (Giacconi et al 1972;Clark et al 1975). With the improvement of X-ray instruments, sources with X-ray luminosities lower than 10 34.5 erg s −1 were discovered with the Einstein Observatory (Hertz & Grindlay 1983) in the 1980s.…”

Section: Introductionmentioning

confidence: 99%

X-Ray and Optical Study of Low Core Density Globular Clusters Ngc6144 and E3

Lan

Kong

Verbunt

et al. 2010

ApJ

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We report on the Chandra X-ray Observatory and Hubble Space Telescope (HST) observations of two low coredensity globular clusters, NGC6144 and E3. By comparing the number of X-ray sources inside the half-mass radius to those outside, we found six X-ray sources within the half-mass radius of NGC6144, of which four are expected to be background sources; three X-ray sources are also found within the half-mass radius of E3, of which three are expected to be background sources. Therefore, we cannot exclude the possibility that all our sources are background sources. However, combining the results from X-ray and optical observations, we found that one to two sources in NGC6144 and one source in E3 are likely to be cataclysmic variables and that one source in NGC6144 is an active binary, based on the X-ray and optical properties. The number of faint X-ray sources in NGC6144 and E3 found with Chandra and HST is higher than a prediction based on collision frequency, but is closer to that based on mass. Our observations strongly suggest that the compact binary systems in NGC6144 and E3 are primordial in origin.

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Observations of variable X-ray sources in globular clusters

Cited by 55 publications

References 0 publications

No evidence for a central IMBH in M 15

No evidence for a central IMBH in M 15

X-ray bursts

X-Ray and Optical Study of Low Core Density Globular Clusters Ngc6144 and E3

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