Award Date

5-1-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Committee Member

Bing Zhang

Second Committee Member

Rebecca Martin

Third Committee Member

Zhaohuan Zhu

Fourth Committee Member

Pengtao Sun

Number of Pages

131

Abstract

Binary neutron star (BNS) mergers are supposed to be the sources of a variety of astrophysical transients, including both gravitational wave (GW) and electromagnetic (EM) signals. The types and properties of the post-merger central product contain crucial information for many unsolved physical problems. Since the current GW detectors are not sensitive enough in kHz, only GWs from the inspiral phase can be detected, so that one cannot directly study the central products from GWs. EM signals can serve as probes to infer the type and properties of the central product. When a long-lived neutron star (NS) is formed after the merger instead of a promptly formed black hole (BH), extra energy can be injected to the merger ejecta and power a engine-fed kilonova which is brighter than the typical kilonovae powered by radioactive decay of the neutron-rich ejecta. X-ray internal plateau (a near flat plateau followed by a steep decay) is another type of EM counterpart of BNS mergers. It might come from the newly born magnetar from the merger and the sharp decay could be naturally explained as the collapse the magnetar. In theory, the collapse of the magnetar can also trigger a non-repeating fast radio burst (FRB). If these EM signatures were detected, we would claim that the central product is a long-lived NS. In GW170817, there is no obvious evidence to diagnose whether a long-lived NS was formed or not. In Chapter 2, we generally discuss the constraints one may pose on the maximum mass of a non-spinning neutron star, M_{TOV}, based on the observations and some EoS-independent universal relations of rapidly-spinning neutron stars. In Chapter 3, we study the X-ray transient XRT210423, which has the feature of X-ray internal plateau. We test the compliance of the data with this model and find that they are generally consistent. Then we use the observed duration and flux of the X-ray signal as well as upper limits of optical emission to pose constraints on the parameters of the underlying putative magnetar. In Chapter 4, we study the dynamical evolution of the engine-fed kilonova (mergernova) ejecta in detail. We perform a semi-analytical study of the problem by adopting a modified mechanical blastwave model that invokes interaction between a Poynting-flux-dominated flow and a non- magnetized massive ejecta. Shortly after the engine is turned on, a pair of shocks would be excited. We find that contrary to the previous assumption, efficient heating only happens before the forward shock breaks out of the ejecta with a heating efficiency Et ~ (0.006 - 0.3). In Chapter 5, we use Monte Carlo simulations to study whether there are genuine non-repeating FRBs. We predict that future continuous monitoring of FRBs with CHIME or similar wide-field radio telescopes would obtain a peak fraction of the repeaters less than 0.04. The detection of a smaller peak value (< 0.04) in the near future would disfavor the ansatz that “all FRB sources repeat”.

Keywords

fast radio transients; gamma-ray bursts; gravitational waves; MHD; neutron star mergers; X-ray transient sources

Disciplines

Astrophysics and Astronomy

File Format

pdf

File Size

3200 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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