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Title: Thermal emission from magnetised neutron stars
Author: Gonzalez-Caniulef, Denis
ISNI:       0000 0004 7970 6187
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2019
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X-ray dim isolated neutron stars and magnetars are neutron stars with strong magnetic fields, B 1013 1015 G. Under these magnetic fields, the properties of the matter and the vacuum are expected to change dramatically. As such, these sources are (unique) natural laboratories for studying fundamental physics in the strong magnetic field regime. In this thesis, I study the polarised thermal emission from both X-ray dim isolated neutron stars and magnetars. First, I developed a ray tracing code that allows me to compute the polarisation properties of X-ray dim isolated neutron stars by considering different surface emission models and by accounting for QED vacuum birefringence effects. I show that combined optical and X-ray polarimetric observations can allow us to infer the state of the matter at the surface of X-ray dim isolated neutron stars. Then, these models are confronted with the optical VLT polarimetric observation of RX J1856.5-3754, the nearest and brightest X-ray dim isolated neutron star. I found that the observed polarisation fraction, 16 5%, can be explained if vacuum birefringence is present, the first ever evidence for this QED effect. In order to confirm this measurement by future missions of Xray polarimetry, I model the polarisation properties of magnetars, active sources with outburst activity in which the X-ray flux decay is explained in the context of an untwisting magnetosphere. I show that if both vacuum birefringence and an untwisting magnetosphere are present, then during the X-ray flux decay of the source, the polarisation angle can change up to 23 (for an untwisting of DF = 0:5 rad). Finally, I model the atmosphere of magnetars heated by a particle bombardment. I compute the thermal emission in the case of a grey atmosphere and discuss the potential spectrum of the source and polarisation signal.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available