A Study of Long Thermonuclear X-Ray Bursts From Neutron Stars

Khaled Alizai

    Research output: Book/ReportPh.D. thesis

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    Thermonuclear X-ray bursts are flares that occur on the surface of neu-tron stars in binary star systems. The typical duration of these events is 10 − 100 s, and they rival the brightest cosmic objects in the X-ray sky in intensity. In the last couple of decades two new classes of rare and extreme energetic X-ray bursts have emerged, intermdiate-duration X-ray bursts and superbursts. Intermediate-duration bursts have durations of 5 min up to several tens of minutes. They have generally been thought to be an ignition of a thick helium layer on the surface of neutron stars. Even more energetic are the superbursts. Their duration and energy re-lease is up to 1000 times higher than for the common bursts. Superbursts are thought to be caused by the ignition of a deep layer of carbon. These long-duration bursts are ideal candidates for probing the interior and the surrounding environment of neutron stars.

    The purpose of this thesis is to provide a systematically re-analyzed sample of all known long-duration bursts observed to date using state of the art analysis methods, explore the impact of long-duration X-ray bursts on their environment, and utilize the burst sample to probe the interior of neutron stars. We present two catalogues; the first contains 14 intermediate-duration bursts observed with the INTEGRAL satellite, while the second is a catalogue of 84 (all) long-duration bursts observed to date from 40 X-ray sources.

    Furthermore, we test the impact of these bursts on the immediate en-vironment of the sources by varying the persistent flux from the source during a burst and conclude that this can only be detected in the peak of a small population of long bursts from instruments with relatively high spectral resolution and high statistical quality (e.g. RXTE/PCA). We show that the distribution of long-duration bursts both as a function of the total radiated energy and the persistent flux of the sources is in agreement with those reported in previous studies. However, we list 18 bursts with total radiated energies between those of the common bursts and those of intermediate-duration bursts.

    Lastly, we discuss two ongoing projects that aim to utilize the long burst catalogue. First, we present preliminary results of two bolometric light curves from the long bursts catalogue to cooling models. This model provides a way of constraining the ignition depth, yb, and the energy release per unit mass, E18, independently of the recurrence time measurements. Second, we motivate the science case for the marginally long bursts mentioned above by presenting a thorough analysis of an X-ray burst from 4U 1722−30 not previously published.
    Original languageEnglish
    Place of PublicationKgs. Lyngby
    PublisherTechnical University of Denmark
    Number of pages133
    Publication statusPublished - 2021


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