PhD Dissertation - Onur Benli

PhD Dissertation - Onur Benli

INVESTIGATION OF YOUNG NEUTRON STAR POPULATIONS

WITH FALLBACK DISK MODEL

 

 

Onur Benli
Physics
, PhD Dissertation, 2016

 

Thesis Jury

Assoc. Prof. Dr. Ünal Ertan(Thesis Advisor)

Prof. Dr. Mehmet Ali Alpar

Asst. Prof. Dr. Murat Kaya

Prof. Dr. Kazım Yavuz Ekşi

Assoc. Prof. Dr. Hakan Erkut

 

 

Date & Time: 24th, 2016 –  13:40 PM

Place: FENS L067

Keywords : Neutron Stars - Pulsars – Magnetars – Fallback Disks – X-rays - Accretion

 

Abstract

 

Young isolated neutron stars manifest themselves as members of different populations, namely anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs), dim isolated neutron stars (XDINs), rotating radio transients, central compact objects (CCOs) and the so-called “high-magnetic-field'” radio pulsars (HBRPs). In this thesis, we have investigated the long-term evolution, short-term X-ray enhancement/outburst, optical and infra-red disk emission properties and the radio properties of members of different young neutron star populations in the frame of the fallback disk model. (i) We have first investigated the X-ray enhancement and the long-term evolution of the recently discovered second “low-B magnetar” Swift J1822.3--1606. The model could produce the observed long-term source properties (period, period derivative, X-ray luminosity) simultaneously. During a soft gamma burst episode, the inner disk matter is pushed back to larger radii, forming a density gradient at the inner disk. Subsequent relaxation of the inner disk could account for the observed X-ray enhancement light curve of Swift J1822.3--1606. (ii) We could accounted for the long-term evolution and the X-ray outburst light curve of a typical AXP/SGR source, SGR 0501+4516, with the similar technique applied to Swift J1822.3--1606. We have further shown that the optical/infrared data of SGR 0501+4516 are in good agreement with the emission from an irradiated fallback disk. In two separate works, we have applied the fallback disk model to (iii) six XDIN and (iv) twelve AXP/SGR sources with relatively well constrained X-ray luminosity and rotational properties. We have found that the individual source properties (period, period derivative, X-ray luminosity) of AXP/SGRs and XDINs could be obtained with similar basic disk parameters. Our results showed that the XDINs have gone through an accretion epoch in the past, while most of the AXP/SGRs are evolving in the accretion phase at present.