[ITAL]Hubble Space Telescope[/ITAL] Detection of a Quiescent Low-Mass X-Ray Binary Companion in 47 Tucanae

Edmonds, P. D.; Heinke, C. O.; Grindlay, Jonathan E.

doi:10.1086/338776

Cited by 27 publications

(43 citation statements)

References 18 publications

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“…As expected, the optical ID for X5/W58 (Edmonds et al 2002b), a qLMXB, has a relatively high F X =F opt value of 47.8 ( Fig. 19; see also Heinke et al 2003).…”

Section: Qlmxb Searchsupporting

confidence: 72%

An Extensive Census ofHubble Space TelescopeCounterparts toChandraX‐Ray Sources in the Globular Cluster 47 Tucanae. II. Time Series and Analysis

Edmonds

Gilliland

Heinke

et al. 2003

ApJ

Self Cite

109

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We report time series and variability information for the optical identifications of X-ray sources in 47 Tucanae reported in Paper I (at least 22 cataclysmic variables [CVs] and 29 active binaries). The radial distribution of the CVs is indistinguishable from that of the millisecond pulsars (MSPs) detected by Freire et al. A study of the eight CVs with secure orbital periods (two obtained from the Chandra study of Grindlay et al.) shows that the 47 Tuc CVs have fainter accretion disks, in the V band, than field CVs with similar periods. These faint disks and the faint absolute magnitudes (M V ) of the 47 Tuc CVs suggests they have low accretion rates. One possible explanation is that the 47 Tuc objects may be a more representative sample of CVs, down to our detection threshold, than the CVs found in the field (where many low accretion rate systems are believed to be undiscovered), showing the advantages of deep globular cluster observations. The median F X =F opt value for the 47 Tuc CVs is higher than that of all known classes of field CV, partly because of the faint M V values and partly because of the relatively high X-ray luminosities (L X ). The latter are only seen in DQ Her systems in the field, but the 47 Tuc CVs are much fainter optically than most field DQ Her's. Previous work by Edmonds et al. has shown that the four brightest CVs in NGC 6397 have optical spectra and broadband colors that are consistent with DQ Her's having lower than average accretion rates. Some combination of magnetic behavior and low accretion rates may be able to explain our observations, but the results at present are ambiguous, since no class of field CV has distributions of both L X and M V that are consistent with those of the 47 Tuc CVs.The radial distribution of the X-ray detected active binaries is indistinguishable from that of the much larger sample of optical variables (eclipsing and contact binaries and BY Dra variables) detected in previous Wide Field Planetary Camera 2 (WFPC2) studies by Albrow et al. The X-ray properties of these objects (luminosity, hardness ratios, and variability) are consistent with those of active binaries found in field studies, and the F X =F opt distribution is significantly different from those of the CVs and the MSPs that are detected (or possibly detected) in the optical. Despite these results, we examine the possibility that a few of the active binaries are MSPs with main-sequence companions resulting from double exchanges in the crowded core of 47 Tuc. No solid evidence is found for a significant population of such objects, and therefore, using the methods of Grindlay et al., we estimate that the number of MSPs in 47 Tuc with luminosities above 10 30 ergs s À1 is $30-40, near the previous lower limit. We present the results of a new, deeper search for faint low-mass X-ray binaries (LMXBs) in quiescence. One reasonable and one marginal candidate for optical identification of a quiescent LMXB was found (one is already known). Finally, it is shown that the periods of the blue va...

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“…As expected, the optical ID for X5/W58 (Edmonds et al 2002b), a qLMXB, has a relatively high F X =F opt value of 47.8 ( Fig. 19; see also Heinke et al 2003).…”

Section: Qlmxb Searchsupporting

confidence: 72%

An Extensive Census ofHubble Space TelescopeCounterparts toChandraX‐Ray Sources in the Globular Cluster 47 Tucanae. II. Time Series and Analysis

Edmonds

Gilliland

Heinke

et al. 2003

ApJ

Self Cite

109

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“…Edmonds et al (2002b) therefore conclude that the star is smaller than its Roche lobe. We suggest an alternative possibility that the system hosts a 0.8 M ⊙ subgiant donor that has recently started to transfer matter to a 1.4 M ⊙ neutron star.…”

Section: Some Specific Systemsmentioning

confidence: 81%

Globular cluster X-ray sources

Verbunt

Lewin

2006

Compact Stellar X-Ray Sources

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Two new bright X-ray sources in globular clusters, and many less luminous ones in globular clusters and in old open clusters, have been discovered with ROSAT. Accurate positions obtained with ROSAT help identification with optical objects, which however is still very incomplete in globular clusters. One dim globular cluster source has been identified with a recycled radio pulsar; several others may be cataclysmic variables. The four brightest X-ray sources identified in the old open cluster M 67 are puzzling, as we do not understand why they emit X-rays. In comparison with the two old open clusters studied so far, globular clusters are remarkably underluminous in X-rays. FirstI am grateful to the organizers of this meeting for the opportunity to contribute to this celebration of the 65 th birthday of Joachim Trümper. During my years (1985)(1986)(1987)(1988)(1989) at the Max Planck Institut für extraterrestrische Physik, I have always felt very much at home, as if an 'honorary German', and I thank Joachim and my other colleagues for this. I was impressed with the width and depth of Joachim Trümper's interests, and thoroughly enjoyed my many discussions with him.The deadline for the first Announcement of Opportunity for observing with ROSAT was on a Sunday evening, at midnight (in checking the date, I find it was on my birthday!). Joachim Trümper was in his office that night, to sign proposals until just before the deadline, or almost, as 11 copies needed to be made for submission. Some of the proposals he signed that night contributed to the results discussed in this review.

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“…For X5, the measured 8.7 hr orbit (Heinke et al 2003) and the main-sequence-like optical counterpart (Edmonds et al 2002) imply that the donor star is not a compact He star or C-O white dwarf and hence is hydrogen rich. Therefore, the NS almost certainly has a pure hydrogen atmosphere.…”

Section: Chemical Composition Of the Atmospherementioning

confidence: 94%

Neutron Star Mass–radius Constraints of the Quiescent Low-Mass X-Ray Binaries X7 and X5 in the Globular Cluster 47 Tuc

Bogdanov

Heinke

Özel

et al. 2016

ApJ

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112

141

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We present Chandra/ACIS-S subarray observations of the quiescent neutron star (NS) low-mass X-ray binaries X7 and X5 in the globular cluster 47Tuc. The large reduction in photon pile-up compared to previous deep exposures enables a substantial improvement in the spectroscopic determination of the NS radius and mass of these NSs. Modeling the thermal emission from the NS surface with a non-magnetized hydrogen atmosphere and accounting for numerous sources of uncertainties, we obtain for the NS in X7 a radius of = -+ R 11.1 0.7 0.8 km for an assumed stellar mass of M=1.4 M e (68% confidence level). We argue, based on astrophysical grounds, that the presence of a He atmosphere is unlikely for this source. Due to the excision of data affected by eclipses and variable absorption, the quiescent low-mass X-ray binary X5 provides less stringent constraints, leading to a radius of = -+ R 9.6 1.1 0.9 km, assuming a hydrogen atmosphere and a mass of M=1.4 M e . When combined with all existing spectroscopic radius measurements from other quiescent low-mass X-ray binaries and Type I X-ray bursts, these measurements strongly favor radii in the 9.9-11.2 km range for a ∼1.5 M e NS and point to a dense matter equation of state that is somewhat softer than the nucleonic ones that are consistent with laboratory experiments at low densities.

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[ITAL]Hubble Space Telescope[/ITAL] Detection of a Quiescent Low-Mass X-Ray Binary Companion in 47 Tucanae

Cited by 27 publications

References 18 publications

An Extensive Census ofHubble Space TelescopeCounterparts toChandraX‐Ray Sources in the Globular Cluster 47 Tucanae. II. Time Series and Analysis

An Extensive Census ofHubble Space TelescopeCounterparts toChandraX‐Ray Sources in the Globular Cluster 47 Tucanae. II. Time Series and Analysis

Globular cluster X-ray sources

Neutron Star Mass–radius Constraints of the Quiescent Low-Mass X-Ray Binaries X7 and X5 in the Globular Cluster 47 Tuc

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