Novel search techniques to detect pulsar black hole binaries in radio observations

Vishnu Balakrishnan
Max-Planck-Institut für Radioastronomie

Pulsars are rapidly rotating highly magnetised neutron stars that emit beams of electromagnetic radiation from their magnetic poles. These compact objects are unique as they are one of the densest forms of matter known in the Universe. Discovering pulsars are a gateway to new and exciting science as they have a wide range of scientific applications from studies of strong-field tests of gravity, neutron star physics and cosmology being a few examples. While all pulsars have their own applications, the bulk of my talk will concentrate on the techniques involved in finding new relativistic binary pulsars particularly the yet to be detected pulsar black-hole binary (PSR-BH) which can be used to test General Relativity and alternate theories of gravity in the quasi-stationary strong-field regime. As I will describe, in my thesis work I improved on our detection sensitivity towards PSR-BH binaries by a factor of 2-2.5 that was achieved purely by changing the search algorithm. I will present the results of my comprehensive search for recycled and unrecycled PSR-BH binaries in circular orbits in the High Time Resolution Universe South Low Latitude Survey (HTRU-S lowlat) using the template-bank algorithm. I will give details about the 20 new pulsars that were found from my searches including a new millisecond pulsar J1743−24 which is a rare intermediate spin-period pulsar in a 70.7-day orbit around a light companion star. Using our non-detections of PSR-BH binaries, I will also present limits on short orbital period PSR-BH binaries near the Galactic-Plane (|b| < 3.5 deg). I will also describe a novel Machine-learning (ML) pulsar candidate classifier using Semi-Supervised Generative Adversarial Networks (SGAN) which achieved better classification performance than the standard supervised algorithms commonly used in the literature using majority unlabelled datasets. Additionally, I will also present the results of the first fully coherent GPU-based radio pulsar search pipeline that can search across all five Keplerian parameters. We compare results from my pipeline to standard time and frequency domain acceleration and jerk search pipelines currently used in the literature. I will discuss its computational feasibility and the binary parameter spaces that have opened up that were previously not accessible. [Referees: Prof. Dr. Michael Kramer, Prof. Dr. Norbert Langer, Prof. Dr. Simon Stellmer, Prof. Dr. Volkmar Gieselmann]