The space density of cataclysmic variables: constraints from the ROSAT North Ecliptic Pole survey

Pretorius, Magaretha L.; Knigge, Christian; O’Donoghue, D.; Henry, J. P.; Gioia, I. M.; Mullis, C. R.

doi:10.1111/j.1365-2966.2007.12461.x

Cited by 68 publications

(90 citation statements)

References 75 publications

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“…For a maximum distance of 2 kpc the model is dominated by the Galactic disk whereas the bulge is not relevant. The resulting number of CVs, regardless of the selection effects that these systems would be subjected to in order to be detected, is 0.18 and 0.54 for a local CV density 1 × 10 −5 and 3 × 10 −5 pc −3 , respectively (these values cover the range of densities found in recent studies; see, e.g., Ak et al 2008;Grindlay et al 2005;Pretorius et al 2007). The probability to detect 3 or more nearby CVs when in fact ∼ 0.54 are expected is low ( 1% for a Poisson distribution).…”

Section: Distance Constraints For the CV Candidatesmentioning

confidence: 98%

ChaMPlaneDEEP GALACTIC BULGE SURVEY. I. FAINT ACCRETION-DRIVEN BINARIES IN THE LIMITING WINDOW

Berg

Hong

Grindlay

2009

ApJ

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We have carried out a deep X-ray and optical survey with Chandra and HST of low-extinction regions in the Galactic bulge. Here we present the results of a search for low-luminosity (L X 10 34 erg s −1 ) accreting binaries among the Chandra sources in the region closest to the Galactic center, at an angular offset of 1.• 4, that we have named the Limiting Window. Based on their blue optical colors, excess Hα fluxes, and high X-ray-to-optical flux ratios, we identify three likely accreting binaries; these are probably white dwarfs accreting from low-mass companions (cataclysmic variables; CVs) although we cannot exclude that they are quiescent neutron-star or black-hole lowmass X-ray binaries. Distance estimates put these systems farther than 2 kpc. Based on their Hα-excess fluxes and/or high X-ray-to-optical flux ratios, we find 22 candidate accreting binaries; however, the properties of some can also be explained if they are dMe stars or active galaxies. We investigate the CV number density toward the bulge and find that the number of observed candidate CVs is consistent with or lower than the number expected for a constant CV-to-star ratio that is fixed to the local value. Our conclusions are limited by uncertainties in the extinction (for which we see a ∼ 30% variation in our 6. 6 × 6. 6 field) and selection effects. The X-ray properties of two likely CVs are similar to those of the faint, hard X-ray sources in the Galactic center region that have been suggested to be (mainly) magnetic CVs. If our candidates belong to the same population, they would be the first members to be optically identified; optical or infrared identification of their Galactic center analogs would be impossible due to the higher obscuration. We speculate that all Galactic hard X-ray sources in our field can be explained by magnetic CVs.

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Section: Distance Constraints For the CV Candidatesmentioning

confidence: 98%

ChaMPlaneDEEP GALACTIC BULGE SURVEY. I. FAINT ACCRETION-DRIVEN BINARIES IN THE LIMITING WINDOW

Berg

Hong

Grindlay

2009

ApJ

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“…Our current understanding of the CV population suggests that the long period systems are typically younger than the short period systems and so-called period bouncers, and consequently have different spatial distributions with respect to the Galactic plane (e.g. Pretorius et al 2007a;Pretorius et al 2007b). However, since the majority of sources in our sample are long period systems, we expect that their distribution scale hight is about 120-150 pc (e.g.…”

Section: Spatial Distributionmentioning

confidence: 99%

Properties of the Galactic population of cataclysmic variables in hard X-rays

Revnivtsev

Sazonov

Krivonos

et al. 2008

A&A

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We measure the spatial distribution and hard X-ray luminosity function of cataclysmic variables (CVs) using the INTEGRAL all-sky survey in the 17-60 keV energy band. −46 pc. The CV luminosity function measured with INTEGRAL in hard X-rays is compatible with that previously determined at lower energies (3-20 keV) using a largely independent sample of sources detected by RXTE (located at |b| > 10• as opposed to the INTEGRAL sample, which is strongly concentrated to the Galactic plane). The cumulative 17-60 keV luminosity density of CVs per unit stellar mass is found to be (1.3 ± 0.3) × 10 27 erg s −1 M −1 , which is comparable to that of low-mass X-ray binaries in this energy band. Therefore, faint but numerous CVs are expected to provide an important contribution to the cumulative hard X-ray emission of galaxies.

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“…The volume probed per XMM-pointing is ∼1.1 × 10 5 pc 3 . The CV space density is not well known, with recent observational constraints derived from the ROSAT Bright Survey (Schwope et al 2002) and the ROSAT NEP Survey (Pretorius et al 2007) for non-magnetic CVs giving ρ ∼ 1.5 × 10 −6 . .…”

Section: Properties and Characteristics Of The Xgps Source Samplementioning

confidence: 99%

The X-ray source content of the XMM-Newton Galactic plane survey

Motch

Warwick

Cropper

et al. 2010

A&A

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We report the results of an optical campaign carried out by the XMM-Newton Survey Science Centre with the specific goal of identifying the brightest X-ray sources in the XMM-Newton Galactic plane survey. In addition to photometric and spectroscopic observations obtained at the ESO-VLT and ESO-3.6 m, we used cross-correlations with the 2XMMi, USNO-B1.0, 2MASS, and GLIMPSE catalogues to advance the identification process. Active coronae account for 16 of the 30 positively or tentatively identified X-ray sources and exhibit the softest X-ray spectra. Many of the identified hard X-ray sources are associated with massive stars, possible members of binary systems and emitting at intermediate X-ray luminosities of 10 32−34 erg s −1 . Among these are (i) a very absorbed, likely hyper-luminous star with X-ray/optical spectra and luminosities comparable to those of η Carina; (ii) a new X-rayselected WN8 Wolf-Rayet star in which most of the X-ray emission probably arises from wind collision in a binary; (iii) a new Be/X-ray star belonging to the growing class of γ-Cas analogues; and (iv) a possible supergiant X-ray binary of the kind discovered recently by INTEGRAL. One of the sources, XGPS-25, has a counterpart of moderate optical luminosity that exhibits HeII λ4686 and Bowen CIII-NIII emission lines, suggesting that this may be a quiescent or X-ray shielded low mass X-ray binary, although its X-ray properties might also be consistent with a rare kind of cataclysmic variable (CV). We also report the discovery of three new CVs, one of which is a likely magnetic system displaying strong X-ray variability. The soft (0.4-2.0 keV) band log N(>S )−log S curve is completely dominated by active stars in the flux range of 1 × 10 −13 to 1 × 10 −14 erg cm −2 s −1 . Several active coronae are also detected above 2 keV suggesting that the population of RS CVn binaries contributes significantly to the hard X-ray source population. In total, we are able to identify a large fraction of the hard (2-10 keV) X-ray sources in the flux range of 1 × 10 −12 to 1 × 10 −13 erg cm −2 s −1 with Galactic objects at a rate consistent with what is expected for the Galactic contribution alone.

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The space density of cataclysmic variables: constraints from the ROSAT North Ecliptic Pole survey

Cited by 68 publications

References 75 publications

ChaMPlaneDEEP GALACTIC BULGE SURVEY. I. FAINT ACCRETION-DRIVEN BINARIES IN THE LIMITING WINDOW

ChaMPlaneDEEP GALACTIC BULGE SURVEY. I. FAINT ACCRETION-DRIVEN BINARIES IN THE LIMITING WINDOW

Properties of the Galactic population of cataclysmic variables in hard X-rays

The X-ray source content of the XMM-Newton Galactic plane survey

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