Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session L3: The Physics of X-Ray Bursts |
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Sponsoring Units: DNP DAP Chair: Ed Brown, Michigan State University Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), St. Louis E |
Sunday, April 13, 2008 1:30PM - 2:06PM |
L3.00001: The complex and puzzling phenomenology of thermonuclear X-ray bursts Invited Speaker: Thirty years of observations of thermonuclear (type-I) bursts from accreting neutron stars have revealed a surprisingly rich spectrum of behavior. A few sources which have been studied intensively offer confirmed examples of the three classes of ignition predicted theoretically, and these systems serve as crucial test-cases for numerical models. However, the behavior of the majority of systems cannot be fully reconciled with theoretical predictions, suggesting there is additional physics at work. Some types of burst behavior are not amenable to study via observations of individual sources, typically because they occur rarely and/or unpredictably. A more promising approach lies in combining data from multiple sources. To date, many thousands of bursts have been detected by various instruments, and new observations are continually adding to the available data. I will describe the results from one such study, involving all the public observations to date made by the {\it Rossi X-ray Timing Explorer}\/ ({\it RXTE}), totalling 1185 bursts from 48 sources. The capabilities of the Proportional Counter Array onboard RXTE enable detailed studies of photospheric radius-expansion, weak bursts (including short recurrence time bursts) and burst oscillations. The two most prolific bursters in the sample exhibit distinctly different bursting properties, suggesting different accreted compositions in the accreted fuel, and highlighting the diversity in burst behaviour which must be considered when combining burst samples. Large burst samples can also be used to measure the global variation of burst properties as a fucntion of accretion rate, to compare with theoretica models. I will also describe a successor project, the Multi-Instrument Burst ARchive (MINBAR), which aims to collate all bursts observed by modern instruments to enable comprehensive future studies of rare events and broad-scale behavior. [Preview Abstract] |
Sunday, April 13, 2008 2:06PM - 2:42PM |
L3.00002: Models of X-ray Bursts Invited Speaker: Type I X-ray bursts are thermonuclear explosions that occur on the surfaces of neutron stars that accrete matter from their binary companions. Since their discovery over 30 years ago, observers have detected thousands of X-ray bursts, while theorists have developed X-ray burst models with ever-increasing complexity and sophistication. While there is now some accord between theory and observations, a few severe discrepancies remain. Chief among them is the range of accretion rates within which thermonuclear burning triggers X-ray bursts. In this talk, I will review our current understanding of the physics of the thermal instability that triggers X-ray bursts, with an emphasis on the pertinent nuclear reactions. In particular, I will discuss the roles that both the hot CNO cycles and their breakout reactions $^{15}$O($\alpha$,$\gamma$)$^{19}$Ne and $^{18}$Ne($\alpha$,$p$)$^{21}$Na play in the stability of thermonuclear burning and the rising phase of X-ray bursts. [Preview Abstract] |
Sunday, April 13, 2008 2:42PM - 3:18PM |
L3.00003: Progress in nuclear physics experiments for the study of X-ray bursts Invited Speaker: Neutron stars in close binary star systems often accrete matter from their companion star. Thermonuclear ignition of the accreted material in the atmosphere of the neutron star leads to a thermonuclear explosion which is observed as an X-ray burst occurring periodically between hours and days depending on the accretion rate. However, the underlying nuclear processes that power the X-ray bursts are often difficult to measure in accelerator-based laboratories. In this talk, I will discuss recent experimental progress in nuclear physics for the input of X-ray bursts model simulations. In particular, I will present new experiments on the measurements of nuclear breakout reactions from the hot CNO cycle that are critical to the ignition conditions of X-ray bursts. Recent measurements of reaction rates along the rp- and $\alpha$p- process path that determine the X-ray burst light curves will also be discussed. Astrophysical implications of the experimental results will be explored within the context of X-ray burst models. [Preview Abstract] |
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