**Autors:** Tasheva, R. P., Stefanov, I. Z.
**Title:** Estimation of the mass and the spin of the neutron star 4U 1728-34 using triples of x-ray quasi-periodic oscillations
**Keywords:** neutrons stars, X-ray quasiperiodic oscillations, pulsars**Abstract:** X-ray quasi-periodic oscillations (QPOs) were reported for 19 different observations of the atoll source 4U 1728-34. Three of them reveal triplets of QPOs: a lower and a upper kHz QPOs and a low-frequency QPO. Even though they are discernible only after averaging we assume them to be simultaneous. We apply a separate model (formula) for each of the three frequencies of the observed QPOs and compose a system which contains three algebraic equations for the three unknown parameters - the mass and the specific angular momentum of the central neutron star, and the radius of the orbit of origin of the given triplet of QPOs, which allows us to find the numerical values of the later. Error propagation formulas are applied for the obtaining of interval estimates of the parameters of the star. This is done through implicit function differentiation. The calculations are repeated with several different models for the kHz QPOs.
**References**
**Issue**
| 48th International Conference on Applications of Mathematics in Engineering and Economics, AMEE 2022, Sofia 7 – 13 June 2022, Code 195286, vol. 2939, issue 1, pp. 090003, 2023, United States, American Institute of Physics Inc., ISSN 0094243X, ISBN 978-073544763-9, https://doi.org/10.1063/5.0178741 |
Copyright American Institute of Physics Inc. |