MSc. Thesis Defense: Ali Arda Gençali

MSc. Thesis Defense: Ali Arda Gençali




Ali Arda Gençali
Physics, MSc. Thesis, 2018


Thesis Jury

Assoc. Prof. Ünal Ertan (Thesis Advisor),

Prof. Ali Alpar, Prof. Kazım Yavuz Ekşi



Date & Time: June 27th, 2018 –  12:30 PM

Place: FENS G032

Keywords : Neutron Stars, Accretion, Accretion Discs - Pulsars, RRATs, J1819-1458








A series of detailed work on the long-term evolutions of young neutron star populations, namely anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs), dim isolated neutron stars (XDINs), ``high-magnetic-field'' radio pulsars (HBRPs), and central compact objects (CCOs) showed that the X-ray luminosities, L_X, and the rotational properties of these systems can be reached by the neutron stars evolving with fallback discs and conventional dipole fields. Remarkably different individual source properties of these populations are reproduced in the same model as a result of the differences in their initial conditions, magnetic moment, initial rotational period, and the disc properties. In this thesis, we have analyzed the properties of the rotating radio transients (RRATs) in the same model. We have investigate the long-term evolution of J1819-1458, which is the only RRAT detected in X-rays. The period, period derivative and X-ray luminosity of J1819-1458 can be reproduced simultaneously with a magnetic dipole field strength B_0  ~ 5×〖10〗^11 G on the pole of the neutron star, which is much smaller than the field strength inferred from the dipole-torque formula. Reasonable model curves are obtained with disc masses in the range of 0.75 - 3.76 M_⨀, producing the source properties, in the accretion phase at ages ~2×〖10〗^5 yr. Our results are not sensitive to the initial period. We find that J1819-1458 is close to and below the radio pulsar death line with this B_0 and the measured period. The numerical simulations indicate that J1819-1458 is evolving toward the properties of XDINs, which implies that there is a close evolutionary connection between RRATs and XDINs. For 29 RRATs with measured period derivatives and unknown X-ray luminosities, we have estimated the minimum B_0 values in the fallback disc model. These lower limits on the field strengths are sufficiently low such that the actual dipole fields of RRATs could fill the B_0 gap between XDINs and CCOs in this model. Finally, we discuss the possible evolutionary links between RRATs and the other young neutron star populations.