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X-Ray Burst Oscillations: From Flame Spreading to the Cooling WakeType I X-ray bursts are thermonuclear flashes observed from the surfaces of accreting neutron stars (NSs) in low mass X-ray binaries. Oscillations have been observed during the rise and/or decay of some of these X-ray bursts. Those seen during the rise can be well explained by a spreading hot spot model, but large amplitude oscillations in the decay phase remain mysterious because of the absence of a clear-cut source of asymmetry. To date there have not been any quantitative studies that consistently track the oscillation amplitude both during the rise and decay (cooling tail) of bursts. Here we compute the light curves and amplitudes of oscillations in X-ray burst models that realistically account for both flame spreading and subsequent cooling. We present results for several such "cooling wake" models, a "canonical" cooling model where each patch on the NS surface heats and cools identically, or with a latitude-dependent cooling timescale set by the local effective gravity, and an "asymmetric" model where parts of the star cool at significantly different rates. We show that while the canonical cooling models can generate oscillations in the tails of bursts, they cannot easily produce the highest observed modulation amplitudes. Alternatively, a simple phenomenological model with asymmetric cooling can achieve higher amplitudes consistent with the observations.
Document ID
20170002436
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Mahmoodifar, Simin
(Universities Space Research Association Greenbelt, MD, United States)
Strohmayer, Tod
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
March 23, 2017
Publication Date
February 10, 2016
Publication Information
Publication: The Astrophysical Journal
Publisher: The American Astronomical Society
Volume: 818
Issue: 1
ISSN: 0004-637X
e-ISSN: 1538-4357
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN40120
Funding Number(s)
CONTRACT_GRANT: 14-ADAP14-0198
Distribution Limits
Public
Copyright
Other
Keywords
ISM: individual objects (G32.8-0.1
Kes 78) aEuro" ISM: supernova remnants aEuro" stars: individual (2XMM J185114.3

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