Place: Nishina Hall, RIKEN Wako Campus<\/p>\n
Date: Feb. 27 (Tue) 13:30 – 15:00<\/p>\n
Speaker: Prof. Yi-Hua Lam\n(Institute of Modern Physics, Chinese Academy of Sciences)<\/p>\n
Title:\nSensitivity of the SAX J1808.4\u22123658 Photospheric Radius Expansion Bursts to\nThermonuclear Reaction-Rate Variations<\/p>\n
Abstract:\nMore than half of the discovered Type-I X-ray bursters generate photospheric radius expansion (PRE) bursts. Nevertheless, the PRE bursting mechanism is not adequately understood due to the intricate thermo-hydrodynamics, varying accretion rates and non-constant recurrence times throughout a series of consecutive type-I X-ray bursts (XRBs). A set of PRE-burst models matching with observations are highly desired within the community to understand the burst mechanism and evolution of thermo-hydrodynamics, and to unfold the information embedded in X-ray signals, especially the properties of the accreting neutron star of a low-mass X-ray binary, nucleosynthesis, and burst ash composition. To construct these PRE models, identifying and reducing the uncertainties of important thermonuclear reactions are our prime aims.\nHere we investigate the sensitivity of PRE-burst models for the SAX\nJ1808.4\u20133658 X-ray source on the uncertainties in (alpha, p), (alpha,\ngamma), (p, alpha), and (p, gamma) nuclear reaction rates. The fully\nself-consistent PRE-burst models consider the mutual influence between\nchanges in extreme astrophysical conditions and changes in nuclear\nenergy generation throughout the evolution of the sequential bursts.\nThese PRE-burst models are instantiated from the state-of-the-art\none-dimensional multi-zone thermo-hydrodynamic stellar evolution code,\nKEPLER. The impacts of all relevant reaction rates of proton-rich\nisotopes up to around mass 80 are individually studied by scaling up and\ndown the respective reaction rate for a factor of 10. We identify and\npresent a number of uncertain reaction rates that significantly\ninfluence the reproduction of observables (i.e., burst light curves,\nfluences, and recurrence times) and the prediction of burst ashes. The\nPRE-burst model is more sensitive to the change of reaction rates\ncompared to all previous sensitivity studies. Moreover, this is the\nfirst XRB sensitivity study based on direct comparison with\nobservations. In this talk, I will present the sensitivity-study\nresults, deepening our understanding of the nuclear processes that shape\nobservables of PRE bursts, and serving as a guidance for future nuclear\nastrophysics to reduce nuclear uncertainties in PRE models.<\/p>\n","protected":false},"excerpt":{"rendered":"
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