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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| Online Access: | https://arxiv.org/abs/2601.11784 |
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| author | Wang, Y. L. Zelati, F. Coti Parent, E. Marino, A. Rea, N. Dhillon, V. S. Blanco-Pozo, J. Ribas, I. Littlefair, S. P. Yang, Z. H. Zhang, G. B. Guillot, S. Ni, K. R. Wu, J. H. Patruno, A. Cavecchi, Y. Illiano, G. Papitto, A. Ambrosino, F. Liu, B. F. Cheng, H. Q. Feng, H. Hu, J. W. Jin, C. C. Sun, H. Tao, L. Xu, Y. J. Yang, H. N. Yuan, W. Zhao, Q. C. |
| author_facet | Wang, Y. L. Zelati, F. Coti Parent, E. Marino, A. Rea, N. Dhillon, V. S. Blanco-Pozo, J. Ribas, I. Littlefair, S. P. Yang, Z. H. Zhang, G. B. Guillot, S. Ni, K. R. Wu, J. H. Patruno, A. Cavecchi, Y. Illiano, G. Papitto, A. Ambrosino, F. Liu, B. F. Cheng, H. Q. Feng, H. Hu, J. W. Jin, C. C. Sun, H. Tao, L. Xu, Y. J. Yang, H. N. Yuan, W. Zhao, Q. C. |
| contents | EP J171159.4-333253 is a new neutron-star low-mass X-ray binary discovered in outburst by the Einstein Probe (EP) on 2025 June 23, exhibiting clocked type-I X-ray bursts, eclipses and dips. In this paper, we report on the results of the X-ray spectral and timing analyses for EP J171159.4-333253 using data collected by EP and NuSTAR during the first 21 days of the outburst. The X-ray burst recurrence time can be characterized over a subset of nine bursts spanning 1.6 days around the NuSTAR observation, and the result is $t_{\rm rec}=8196 \pm 177\,$s with indications of a possible decreasing trend. From the X-ray eclipse events, the binary orbital period and the eclipse duration are estimated to be $P_{\rm orb}=6.48301 \pm 0.00003\,$hr and $D_{\star,X} = 1245.5^{+6.9}_{-6.5}\,$s, respectively. These enable an estimate of the mass and radius of the companion star and the binary inclination, which are $M_2\approx0.6-0.8\,M_\odot$, $R_2\approx0.7-0.8\,R_\odot$ and $i\approx73-75^\circ$, respectively. We also report on joint ULTRACAM and EP observations on 2025 July 21--22, detecting the source optical counterpart and covering an eclipse in both X-ray and optical bands. The optical eclipse is wavelength-dependent and broader than in X-rays, indicating that part of the optical emission arises from an extended region in the accretion flow. Despite a moderate variation in the source flux, the properties of the persistent X-ray emission are typical of a hard spectral state. We further evaluated the ratio of the accretion energy to the thermonuclear energy to be 120--130, implying helium bursts with the accreted hydrogen being depleted in-between bursts. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_11784 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Einstein Probe discovery of EP J171159.4-333253: an eclipsing neutron star low-mass X-ray binary with clocked bursts Wang, Y. L. Zelati, F. Coti Parent, E. Marino, A. Rea, N. Dhillon, V. S. Blanco-Pozo, J. Ribas, I. Littlefair, S. P. Yang, Z. H. Zhang, G. B. Guillot, S. Ni, K. R. Wu, J. H. Patruno, A. Cavecchi, Y. Illiano, G. Papitto, A. Ambrosino, F. Liu, B. F. Cheng, H. Q. Feng, H. Hu, J. W. Jin, C. C. Sun, H. Tao, L. Xu, Y. J. Yang, H. N. Yuan, W. Zhao, Q. C. High Energy Astrophysical Phenomena EP J171159.4-333253 is a new neutron-star low-mass X-ray binary discovered in outburst by the Einstein Probe (EP) on 2025 June 23, exhibiting clocked type-I X-ray bursts, eclipses and dips. In this paper, we report on the results of the X-ray spectral and timing analyses for EP J171159.4-333253 using data collected by EP and NuSTAR during the first 21 days of the outburst. The X-ray burst recurrence time can be characterized over a subset of nine bursts spanning 1.6 days around the NuSTAR observation, and the result is $t_{\rm rec}=8196 \pm 177\,$s with indications of a possible decreasing trend. From the X-ray eclipse events, the binary orbital period and the eclipse duration are estimated to be $P_{\rm orb}=6.48301 \pm 0.00003\,$hr and $D_{\star,X} = 1245.5^{+6.9}_{-6.5}\,$s, respectively. These enable an estimate of the mass and radius of the companion star and the binary inclination, which are $M_2\approx0.6-0.8\,M_\odot$, $R_2\approx0.7-0.8\,R_\odot$ and $i\approx73-75^\circ$, respectively. We also report on joint ULTRACAM and EP observations on 2025 July 21--22, detecting the source optical counterpart and covering an eclipse in both X-ray and optical bands. The optical eclipse is wavelength-dependent and broader than in X-rays, indicating that part of the optical emission arises from an extended region in the accretion flow. Despite a moderate variation in the source flux, the properties of the persistent X-ray emission are typical of a hard spectral state. We further evaluated the ratio of the accretion energy to the thermonuclear energy to be 120--130, implying helium bursts with the accreted hydrogen being depleted in-between bursts. |
| title | Einstein Probe discovery of EP J171159.4-333253: an eclipsing neutron star low-mass X-ray binary with clocked bursts |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2601.11784 |