ROSAT observations of globular clusters

Johnston, Helen M.; Verbunt, F.; Hasinger, G.

doi:10.1063/1.45952

Cited by 42 publications

(101 citation statements)

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“…The XMM-Newton emission coincides perfectly with the RASS emission in each case. Additionally, the two clusters are also found 40 off-axis in a PSPC pointed observation of a globular cluster, NGC 6752 (Johnston et al 1994), where they are listed as sources within the globular cluster (sources 1 and 2 in Johnston et al's Table 8). Lacking spectroscopic information, Johnston et al (1994) could not specify the exact nature of the sources, which they assumed to be of Galactic origin.…”

Section: Plck G3371−260mentioning

confidence: 99%

Planckearly results. IX.XMM-Newtonfollow-up for validation ofPlanckcluster candidates

Aghanim¹,

Arnaud²,

Ashdown³

et al. 2011

A&A

129

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We present the XMM-Newton follow-up for confirmation of Planck cluster candidates. Twenty-five candidates have been observed to date using snapshot (∼10 ks) exposures, ten as part of a pilot programme to sample a low range of signal-to-noise ratios (4 < S/N < 6), and a further 15 in a programme to observe a sample of S/N > 5 candidates. The sensitivity and spatial resolution of XMM-Newton allows unambiguous discrimination between clusters and false candidates. The 4 false candidates have S/N ≤ 4.1. A total of 21 candidates are confirmed as extended X-ray sources. Seventeen are single clusters, the majority of which are found to have highly irregular and disturbed morphologies (about ∼70%). The remaining four sources are multiple systems, including the unexpected discovery of a supercluster at z = 0.45. For 20 sources we are able to derive a redshift estimate from the X-ray Fe K line (albeit of variable quality). The new clusters span the redshift range 0.09 < ∼ z < ∼ 0.54, with a median redshift of z ∼ 0.37. A first determination is made of their X-ray properties including the characteristic size, which is used to improve the estimate of the SZ Compton parameter, Y 500 . The follow-up validation programme has helped to optimise the Planck candidate selection process. It has also provided a preview of the X-ray properties of these newly-discovered clusters, allowing comparison with their SZ properties, and to the X-ray and SZ properties of known clusters observed in the Planck survey. Our results suggest that Planck may have started to reveal a non-negligible population of massive dynamically perturbed objects that is under-represented in X-ray surveys. However, despite their particular properties, these new clusters appear to follow the Y 500 -Y X relation established for X-ray selected objects, where Y X is the product of the gas mass and temperature.

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Section: Plck G3371−260mentioning

confidence: 99%

Planckearly results. IX.XMM-Newtonfollow-up for validation ofPlanckcluster candidates

Aghanim¹,

Arnaud²,

Ashdown³

et al. 2011

A&A

129

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“…Terzan 5 was observed by ROSAT several times (see e.g. Johnston et al 1995). We focused on a pointing observation centred on Terzan 5 taken in 1991 (ID 300060) by the High Resolution Imager (HRI) instrument with a total live time of 22.5 ks.…”

Section: Rosatmentioning

confidence: 99%

Multi-wavelength environment of the Galactic globular cluster Terzan 5

Clapson

Domainko

Jamrozy

et al. 2011

A&A

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Terzan 5 is a Galactic globular cluster exhibiting prominent X-ray and gamma-ray emission. Following the discovery of extended X-ray emission in this object, we explore here archival data at several wavelengths for other unexpected emission features in the vicinity of this globular cluster. Radio data from the Effelsberg 100-m telescope show several extended structures near Terzan 5, albeit with large uncertainties in the flux estimates and no reliable radio spectral index. In particular, a radio source extending from the location of Terzan 5 to the north-west could result from long-term non-thermal electron production by the large population of milli-second pulsars in this globular cluster. Another prominent radio structure close to Terzan 5 may be explained by ionised material produced by a field O star. As for the diffuse X-ray emission found in Terzan 5, its extension appears to be limited to within 2.5 arcmin of the globular cluster and the available multi-wavelength data is compatible with an inverse Compton scenario but disfavours a nonthermal Bremsstrahlung origin.

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“…Using the n H value of 2.2 × 10 21 cm −2 (Johnston et al 1994) and a power law slope of 2.1 (the average of the 39 detected sources), the unabsorbed flux limit of the Chandra observation is 3×10 −15 erg cm −2 s −1 (0.5-8.0 keV). Using the distance measurement of 3.2 kpc (Harris 1996, December 2010 revision) this translates to an unabsorbed luminosity limit for an object in the cluster of 4 × 10 30 erg s −1 (0.5-8.0 keV).…”

Section: X-ray Observationsmentioning

confidence: 99%

CV1 in the globular cluster M 22: confirming its nature through X-ray observations and optical spectroscopy

Webb¹,

Servillat²

2013

A&A

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Context. Observations of cataclysmic variables in globular clusters appear to show a dearth of outbursts compared to those observed in the field. A number of explanations have been proposed, including low mass-transfer rates and/or moderate magnetic fields implying higher mass white dwarfs than the average observed in the field. Alternatively this apparent dearth may be simply a selection bias. Aims. We examine multi-wavelength data of a new cataclysmic variable, CV1, in the globular cluster M 22 to try to constrain its period and magnetic nature, with an aim at understanding whether globular cluster cataclysmic variables are intrinsically different from those observed in the field. Methods. We use the sub-arcsecond resolution of the Chandra ACIS-S to identify the X-ray counterpart to CV1 and analyse the X-ray spectrum to determine the spectral model that best describes this source. We also examine the low resolution optical spectrum for emission lines typical of cataclysmic variables. Cross correlating the H α line in each individual spectrum also allows us to search for orbital motion. Results. The X-ray spectrum reveals a source best-fitted with a high-temperature bremsstrahlung model and an X-ray unabsorbed luminosity of 1.8 × 10 32 erg s −1 (0.3-8.0 keV), which are typical of cataclysmic variables. Optical spectra reveal Balmer emission lines, which are indicative of an accretion disc. Potential radial velocity in the H α emission line is detected and a period for CV1 is proposed. Conclusions. These observations support the CV identification. The radial velocity measurements suggest that CV1 may have an orbital period of ∼7 h, but further higher resolution optical spectroscopy of CV1 is needed to unequivocally establish the nature of this CV and its orbital period.

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ROSAT observations of globular clusters

Cited by 42 publications

References 0 publications

Planckearly results. IX.XMM-Newtonfollow-up for validation ofPlanckcluster candidates

Planckearly results. IX.XMM-Newtonfollow-up for validation ofPlanckcluster candidates

Multi-wavelength environment of the Galactic globular cluster Terzan 5

CV1 in the globular cluster M 22: confirming its nature through X-ray observations and optical spectroscopy

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