Globular Clusters and X‐Ray Point Sources in Centaurus A (NGC 5128)

Woodley, Kristin A.; Raychaudhury, Somak; Kraft, Ralph; Harris, William E.; Jordán, Andrés; Whitaker, Katherine E.; Jones, Christine; Forman, W.; Murray, Stephen S.

doi:10.1086/529419

Cited by 12 publications

(18 citation statements)

References 70 publications

(166 reference statements)

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“…It has been shown (see Fabbiano (2006) for a review) that a significant fraction of LMXBs observed in early-type galaxies with Chandra are associated with globular clusters (GCs). It has recently been confirmed that 41 X-ray point sources in our Cen A data are associated with GCs within Cen A (Woodley et al 2008;Jordán et al 2007;Voss et al 2009). We examined Spitzer/IRAC 3.6-and 8-µm IR maps (Hardcastle et al 2006) to check for IR counterparts to our jet knots, which would indicate a coincident globular cluster and found a compact IR source for GX3.…”

Section: Point Source Contaminationsupporting

confidence: 74%

Long-Term Monitoring of the Dynamics and Particle Acceleration of Knots in the Jet of Centaurus A

Goodger

Hardcastle

Croston

et al. 2009

ApJ

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We present new and archival multi-frequency radio and X-ray data for Centaurus A obtained over almost 20 years at the VLA and with Chandra, with which we measure the X-ray and radio spectral indices of jet knots, flux density variations in the jet knots, polarization variations, and proper motions. We compare the observed properties with current knot formation models and particle acceleration mechanisms. We rule out impulsive particle acceleration as a formation mechanism for all of the knots as we detect the same population of knots in all of the observations and we find no evidence of extreme variability in the X-ray knots. We find the most likely mechanism for all the stationary knots is a collision resulting in a local shock followed by a steady state of prolonged, stable particle acceleration and X-ray synchrotron emission. In this scenario, the X-ray-only knots have radio counterparts that are too faint to be detected, while the radio-only knots are due to weak shocks where no particles are accelerated to X-ray emitting energies. Although the base knots are prime candidates for reconfinement shocks, the presence of a moving knot in this vicinity and the fact that there are two base knots are hard to explain in this model. We detect apparent motion in three knots; however, their velocities and locations provide no conclusive evidence for or against a faster moving 'spine' within the jet. The radio-only knots, both stationary and moving, may be due to compression of the fluid.

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Section: Point Source Contaminationsupporting

confidence: 74%

Long-Term Monitoring of the Dynamics and Particle Acceleration of Knots in the Jet of Centaurus A

Goodger

Hardcastle

Croston

et al. 2009

ApJ

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“…This being the case, any attempt to perform optical photometry on the source position will be inconclusive. The nearest globular cluster that has been spectroscopically confirmed as belonging to Cen A is ∼30 away from CXOU J132527.6−430023 (Woodley et al 2008). However, no clusters have been detected within the radial distance of the transient from the galaxy center, as a result of the high stellar luminosity within ∼1.…”

Section: Possible Counterpartsmentioning

confidence: 99%

A Transient Sub-Eddington Black Hole X-Ray Binary Candidate in the Dust Lanes of Centaurus A

Burke

Raychaudhury

Kraft

et al. 2012

ApJ

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We report the discovery of a bright X-ray transient CXOU J132527.6−430023 in the nearby early-type galaxy NGC 5128. The source was first detected over the course of five Chandra observations in 2007, reaching an unabsorbed outburst luminosity of (1-2) × 10 38 erg s −1 in the 0.5-7.0 keV band before returning to quiescence. Such luminosities are possible for both stellar-mass black hole and neutron star (NS) X-ray binary transients. Here, we attempt to characterize the nature of the compact object. No counterpart has been detected in the optical or radio sky, but the proximity of the source to the dust lanes allows for the possibility of an obscured companion. The brightness of the source after a >100-fold increase in X-ray flux makes it either the first confirmed transient non-ultraluminous X-ray black hole system in outburst to be subject to detailed spectral modeling outside the Local Group, or a bright (>10 38 erg s −1 ) transient NS X-ray binary, which are very rare. Such a large increase in flux would appear to lend weight to the view that this is a black hole transient. X-ray spectral fitting of an absorbed power law yielded unphysical photon indices, while the parameters of the best-fit absorbed disk blackbody model are typical of an accreting ∼10 M black hole in the thermally dominant state.

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“…As this is steeper than the LF of the field LMXBs, to neglect their contribution may lead to artificially high confidence estimates. Furthermore, the study of Woodley et al (2008) did not take incompleteness effects into account, and they concluded that it was not clear if their analysis was not compromised by the sample incompleteness. The results presented above are therefore the most robust and statistically significant evidence yet for a difference between the luminosity distributions of LMXBs in the field and in globular clusters.…”

Section: Globular Cluster Sourcesmentioning

confidence: 99%

“…This suggestion has been confronted by the statistics of LMXBs and globular clusters in spiral galaxies and especially in the Milky Way. Also, evidence has been found that the luminosity distributions of LMXBs in globular clusters (and in the central parts of M 31) and in the field differ at the low luminosity end, below ∼ 10 37 erg s −1 , (Voss & Gilfanov 2007a;Fabbiano et al 2007;Woodley et al 2008;Kim et al 2009), which would be a strong indication of different formation histories.…”

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confidence: 97%

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LUMINOSITY FUNCTIONS OF LMXBs IN CENTAURUS A: GLOBULAR CLUSTERS VERSUS THE FIELD

Voss

Gilfanov

Sivakoff

et al. 2009

ApJ

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We study the X-ray luminosity function (XLF) of low mass X-ray binaries (LMXB) in the nearby early-type galaxy Centaurus A, concentrating primarily on two aspects of binary populations: the XLF behavior at the low luminosity limit and comparison between globular cluster and field sources. The 800 ksec exposure of the deep Chandra VLP program allows us to reach a limiting luminosity of ∼ 8 · 10 35 erg s −1 , about ∼ 2 − 3 times deeper than previous investigations. We confirm the presence of the low luminosity break in the overall LMXB XLF at log(L X ) ≈ 37.2 − 37.6 below which the luminosity distribution follows a dN/d(ln L) ∼ const law. Separating globular cluster and field sources, we find a statistically significant difference between the two luminosity distributions with a relative underabundance of faint sources in the globular cluster population. This demonstrates that the samples are drawn from distinct parent populations and may disprove the hypothesis that the entire LMXB population in early type galaxies is created dynamically in globular clusters. As a plausible explanation for this difference in the XLFs, we suggest that there is an enhanced fraction of helium accreting systems in globular clusters, which are created in collisions between red giants and neutron stars. Due to the 4 times higher ionization temperature of He, such systems are subject to accretion disk instabilities at ≈ 20 times higher mass accretion rate, and therefore are not observed as persistent sources at low luminosities.

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Globular Clusters and X‐Ray Point Sources in Centaurus A (NGC 5128)

Cited by 12 publications

References 70 publications

Long-Term Monitoring of the Dynamics and Particle Acceleration of Knots in the Jet of Centaurus A

Long-Term Monitoring of the Dynamics and Particle Acceleration of Knots in the Jet of Centaurus A

A Transient Sub-Eddington Black Hole X-Ray Binary Candidate in the Dust Lanes of Centaurus A

LUMINOSITY FUNCTIONS OF LMXBs IN CENTAURUS A: GLOBULAR CLUSTERS VERSUS THE FIELD

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