| Description |
Intense X-ray bursts (type-I bursts), originated from runaway thermonuclear processes, are observed from the surfaces of many accreting neutron star Low Mass X-ray Binary (LMXB) systems and they provide an important tool to constrain the neutron star equation of state. I am going to talk about the various properties of such bursts observed in a few LMXBs and how they can be used to infer about the "hot spot" formation and evolution. The 2010 outburst of the transient LMXB IGR J17480–2446 exhibited a series of X-ray bursts as well as millihertz (mHz) quasi-periodic oscillations (QPOs) near the outburst peak. The quite diverse burst properties compared to typical type-I bursts suggested them to be the type-II bursts originating from accretion disc instability. We show that the bursts are indeed of thermonuclear origin and thus confirm the quasi-stable burning model for mHz QPOs. The properties of the smoothly varying periodic bursts are highly dependent on the source spectral states and their variation over a large $\dot{M}$ range reveals evolution of burning processes/ fuels at different accretion rate regimes. 12 such bursts were observed in the RXTE PCA FOV during the 2011 outburst of another similar transient pulsar IGR J17498−2921. We confirm the presence of burst oscillations from this source and from spectroscopy of these bursts infer that the variability in luminosity of the bursts probably indicates to a confined burning scenario. Finally I will talk about how the burst oscillation timing properties can be used provide insight on the flame spreading i.e., whether and how the burning remains constrained and the effects of various physical factors like Coriolis force etc. on the burning front propagation.
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