Simultaneous Chandra and HST observations of the quiescent neutron-star low-mass X-ray binaries in 47 Tucanae
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| Autori principali: | , , , , , , , , |
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| Natura: | Preprint |
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2024
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| _version_ | 1866914768071163904 |
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| author | Berg, Maureen van den Sandoval, Liliana Rivera Heinke, Craig O. Cohn, Haldan N. Lugger, Phyllis M. Grindlay, Jonathan E. Edmonds, Peter D. Anderson, Jay Catuneanu, Andrei |
| author_facet | Berg, Maureen van den Sandoval, Liliana Rivera Heinke, Craig O. Cohn, Haldan N. Lugger, Phyllis M. Grindlay, Jonathan E. Edmonds, Peter D. Anderson, Jay Catuneanu, Andrei |
| contents | We present simultaneous Chandra X-ray Observatory and Hubble Space Telescope observations of three certain (X5, X7, W37) and two likely (X4, W17) quiescent neutron-star low-mass X-ray binaries (qLMXBs) in the globular cluster 47 Tuc. We study these systems in the X-ray, optical and near-ultraviolet (NUV) using the simultaneous data and additional non-contemporaneous HST data. We have discovered a blue and variable NUV counterpart to W17. We have not securely identified the eclipsing qLMXB W37 in the optical or NUV. Deeper high-resolution imaging is needed to further investigate the faint NUV excess near the centre of the W37 error circle. We suggest that a previously identified optical astrometric match to X7 is likely the true counterpart. The Halpha emission and the location of the counterpart in the colour-magnitude diagram, indicate that the secondary is probably a non-degenerate, H-rich star. This is consistent with previous results from fitting X7's X-ray spectrum. In X4, the simultaneous X-ray and optical behaviour supports the earlier suggestion that the X-ray variability is driven by changes in accretion rate. The X-ray eclipses in X5 coincide with minima in the optical/NUV light curves. Comparison of the 47 Tuc qLMXBs with the cataclysmic variables (CVs) in the cluster confirms that overall the qLMXBs have larger X-ray-to-optical flux ratios. Based on their optical/NUV colors, we conclude that the accretion disks in the qLMXBs are less prominent than in CVs. This makes the ratio of X-ray flux to excess blue optical flux a powerful discriminator between CVs and qLMXBs. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2404_15504 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Simultaneous Chandra and HST observations of the quiescent neutron-star low-mass X-ray binaries in 47 Tucanae Berg, Maureen van den Sandoval, Liliana Rivera Heinke, Craig O. Cohn, Haldan N. Lugger, Phyllis M. Grindlay, Jonathan E. Edmonds, Peter D. Anderson, Jay Catuneanu, Andrei High Energy Astrophysical Phenomena We present simultaneous Chandra X-ray Observatory and Hubble Space Telescope observations of three certain (X5, X7, W37) and two likely (X4, W17) quiescent neutron-star low-mass X-ray binaries (qLMXBs) in the globular cluster 47 Tuc. We study these systems in the X-ray, optical and near-ultraviolet (NUV) using the simultaneous data and additional non-contemporaneous HST data. We have discovered a blue and variable NUV counterpart to W17. We have not securely identified the eclipsing qLMXB W37 in the optical or NUV. Deeper high-resolution imaging is needed to further investigate the faint NUV excess near the centre of the W37 error circle. We suggest that a previously identified optical astrometric match to X7 is likely the true counterpart. The Halpha emission and the location of the counterpart in the colour-magnitude diagram, indicate that the secondary is probably a non-degenerate, H-rich star. This is consistent with previous results from fitting X7's X-ray spectrum. In X4, the simultaneous X-ray and optical behaviour supports the earlier suggestion that the X-ray variability is driven by changes in accretion rate. The X-ray eclipses in X5 coincide with minima in the optical/NUV light curves. Comparison of the 47 Tuc qLMXBs with the cataclysmic variables (CVs) in the cluster confirms that overall the qLMXBs have larger X-ray-to-optical flux ratios. Based on their optical/NUV colors, we conclude that the accretion disks in the qLMXBs are less prominent than in CVs. This makes the ratio of X-ray flux to excess blue optical flux a powerful discriminator between CVs and qLMXBs. |
| title | Simultaneous Chandra and HST observations of the quiescent neutron-star low-mass X-ray binaries in 47 Tucanae |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2404.15504 |