PhD colloquium, location: Auditorium 0.01, MPIfR
Jiwoong Jang
Pulsars and Gravitational Waves
Pulsars are magnetized rotating neutron stars that formed from the collapsed core of a massive star following a supernova. A misalignment between the beam emission axis (magnetic axis) and rotation axis causes them to appear as a pulsating radio source. The emitted signals from pulsars undergo delays due to their position, motion, relativistic effects and the effects of the interstellar medium. By analyzing and modelling the arrival times of pulses by accounting for every rotation of the pulsar, those physical parameters can be measured. This technique is called pulsar timing. Pulsar timing measurements provide various applications to fundamental physics and astronomy. In this PhD defense, I will present pulsar timing analysis for a single pulsar, PSR J1439−5501, as well as the first evidence for the gravitational wave background.
PSR J1439−5501 is a binary system, consisting of a pulsar and an unusually massive white dwarf companion (1.0–1.3 M☉). Measuring masses and other physical characteristics of such unique systems provide hints for binary star evolution. A relativistic phenomenon, Shapiro delay, in PSR J1439−5501 allows us to measure masses but had not yet been observed. I detected a signature of Shapiro delay via timing analysis and investigated it to measure pulsar mass and companion mass. I analyzed pulsar scintillation, which occurs due to interference between photons emitted from the pulsar travelling along different paths through the interstellar medium, to measure distance to the pulsar. Using simulation and the result of timing and scintillation, I discuss the future study of PSR J1439−5501.
Cosmological phenomena such as super massive black hole binaries (SMBHBs) formed during galaxy mergers are expected to cause low-frequency gravitational waves (GWs). An array of pulsars, called pulsar timing array (PTA), can be used as a detector of such GWs, and this will enable us to understand the galaxy evolution. I led the data production of 25 pulsars, which were used to search for nano-hertz GWs. Using those data, we found the first evidence of the GWs, potentially caused by SMBHBs. Our spectral analysis of GWs also showed deviation between our observation and model, which will enable us to measure the dynamics of SMBHBs as well as their formation and evolution.