Transients, Pulsars and High-Energy Astrophysics

Machine Learning and Citizen Science in search of Radio Transients.
Rob Fender and Chris Lintott

The ability to find unusual objects in large datasets is a critical skill across much of modern astrophysics. This project will develop techniques to search for transient sources in data from the SKA precursor, MeerKAT, which will carry out by far the largest GHz-frequency radio transient search. MeerKAT is already finding transients, and the expected rate appears to be high, providing plenty of opportunity for interesting astrophysics. In classifying what MeerKAT finds, we will also draw on data from the optical telescope MeerLICHT which carries out simultaneous observations. It combines Oxford's expertise in radio astronomy, particularly transients, with our leadership of the Zooniverse citizen science project. In combining classifications from hundreds of thousands of volunteers with modern machine learning, particularly Bayesian convolutional neural networks, the aim is to develop a reliable classifier that produces a stream of interesting follow-up opportunities.

A successful student would be supervised by Rob Fender, who leads the MeerKAT transient search, and Chris Lintott, who is the Principal Investigator for Zooniverse.

Further reading:

ThunderKAT: https://arxiv.org/abs/1711.04132
Zooniverse transient searches: https://arxiv.org/abs/1707.05223
Combining Bayesian machine learning and citizen science: https://arxiv.org/abs/1905.07424

Understanding the population of radio pulsars.
Aris Karastergiou

Using pulsars for experiments in fundamental physics relies more and more on our understanding of the objects themselves. What are their orientations in space? What is the origin of their radio emission and how does it relate to the rotating star? Modern surveys with the MeerKAT telescope in South Africa will provide the data for measurements of radio emission also at multiple epochs, providing an additional axis to separate those effects that are intrinsic to the star from those related to propagation of the radiation through the intervening media. The student will work within an international collaboration (www.meertime.org) to explore the characteristics of a large population of pulsars, monitored through the so-called Thousand Pulsar Array. Results from this project directly feed into our understanding of the cold and dense nuclear matter in neutron star interiors, the plasma physics processes the occur in pulsar magnetospheres, the properties of the ionized and magnetized interstellar medium, the birth and evolution of neutron stars, and interpretation of the neutron star population in the context of modern results in gravitational wave astrophysics.

Pulsar evolution through Radio- X-ray correlations.
Aris Karastergiou & Bettina Posselt

This project will use high quality data from Radio and X-ray observatories to explore how Pulsars evolve. Existing observations of X-Ray - Radio correlations reveal connections between the emission processes, but this work has so far been limited to a very small number of sources. Extending observations of such correlations to Pulsars of different age, and perhaps more importantly, different spin-down energy (Edot), this project aims to address questions regarding the orientation, structure, and physical properties of pulsar magnetospheres, and the underlying magnetic field. How do these properties evolve with Pulsar age? Radio data will mostly come from the MeerKAT Thousand Pulsar Array survey, which has the potential to reveal a new population of "interesting" pulsars that can also be studied through XMM-Newton or NICER data in X-rays. The student will undertake original research attempting to straddle the gap between Radio and X-ray Pulsar science, with the support of local experts and international collaborators.

Discovery of new microquasars.
Katherine Blundell

The proposed project will make use of the Many Commensal Cameras (MC2) data streams from the worldwide Global Jet Watch observatories that are making sensitive, successive observations of the signatures of precessing jets exhibited by microquasars in our Galaxy. Promising candidates will be followed-up and investigated via spectroscopy to discern dynamical confirmation of precessing jets moving at relativistic speeds.
Unique data streams for this student project are assured, from the five Global Jet Watch observatories around the planet (PI K Blundell; www.GlobalJetWatch.net).

Very high-energy gamma ray astrophysics.
Garret Cotter

Very high-energy (VHE) gamma-ray astrophysics is an exciting field spanning fundamental physics and extreme astrophysical processes. We detect the Cherenkov light emitted when VHE gamma rays from space hit the top of the Earth’s atmosphere, using optical telescopes on the ground fitted with high-speed detectors similar to those used by the Large Hadron Collider. Our science goals include
• Understanding the origin of cosmic rays and their role in the Universe.
• Understanding the natures and variety of particle acceleration around black holes.
• Searching for the ultimate nature of matter and physics beyond the Standard Model.
The Oxford group works on the High Energy Stereoscopic System (H.E.S.S.) in Namibia, which is at present the world’s largest gamma-ray observatory, and on the development of international Cherenkov Telescope Array (CTA; http://www.cta-observatory.org/, artist’s conception above). This will be the first global observatory for VHE gamma-ray astronomy, and will be sensitive to photon energies up to 1015 eV.
There are openings for both experimental and theoretical work. We are developing software and data analysis techniques for CTA’s small-sized unit telescopes. These will have 2k pixel detectors and front-end amplifiers which feed into custom high-speed electronics. This gives a system that can image at a rate of a billion frames per second. We are also leading the efforts on machine learning techniques for the large volumes of data that will be generated when CTA becomes operational.
On the theoretical/observational side of the programme, recently we have developed new theoretical models for the broad-spectrum emission from steady-state jets that let us use the gamma-ray observations and those at other wavelengths to investigate the physical properties of the jet and the black hole at its base. We now propose to extend these models to look in particular at the entrainment of heavy particles as the jets propagate through their host galaxy, and the resulting possibility of hadronic particle processes within the jets. We will investigate how CTA may be used to determine the physical conditions that lead to flaring and the presence, and extent, of emission from hadronic processes.
We will offer the possibility of joint supervision with the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg, and all students will have the opportunity to gain experience on observing shifts at the H.E.S.S. site (below).

For more information please contact Professor Garret Cotter (garret.cotter@physics.ox.ac.uk)

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Relativistic Astrophysics with the world’s most powerful radio telescope.
Rob Fender, Ian Heywood (Oxford), and
Michael Kramer (Max Planck Institute for Radio Astronomy, Bonn)

The most extreme phenomena in the Universe since the Big Bang are associated with explosive, transient astrophysical phenomena. The underlying physics of these events ranges from the release of gravitational potential energy as matter falls into black holes, to the explosive merger of two neutron stars and their associated electromagnetic and gravitational wave burst.

Radio emission from such events results from the spiralling of shock-accelerated, relativistic electrons around magnetic field lines, via the synchrotron process. The shock acceleration of the particles and compression and enhancement of the magnetic field result in turn from the supersonic outflow of matter from these transients, usually in the form of highly relativistic, collimated ‘jets’. Although having very large energy content, this sychrotron emission is usually unobservably faint at higher frequencies. Observations with radio telescopes are therefore the only way to study the kinetic output from such transient events, and have revealed it to be a fundamental and powerful channel for the dissipation of the released energy. A prime recent example is the relativistic jet, observed at radio wavelengths, from the neutron star merger and gravitational wave burst event GW170817, in which our team are heavily involved.

MeerKAT is the most powerful radio telescope in the southern hemisphere, and both Oxford and Bonn co-lead projects to study transients with the array over the next five years (via the ThunderKAT and TRAPUM projects). In addition, during this project the telescope will be upgraded with new high-frequency receivers, and expanded to a greater sensitivity and angular resolution, via direct investment from the Max Planck institute in Bonn. The successful applicant will be one of the first users of this extended MeerKAT, helping to commission it and using its ungraded sensitivity to study the kinetic feedback from astrophysical transients in unprecedented detail. Major discoveries await!

This project is jointly funded by Oxford Astrophysics and Max Planck Institute in Bonn, and will make use of the extended MeerKAT radio telescope array in South Africa. As a result, the student will spend at least one year of their studies based in Bonn, working in the relativistic astrophysics group there, and will be expected to make multiple visits to South Africa. In addition, there will be frequent additional travel to collaboration meetings and conferences.

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Relativistic Astrophysics and Machine Learning with the world’s most powerful radio telescope.
Rob Fender, Ian Heywood and Peter Braam (Oxford)
Michael Kramer (Max Planck Institute for Radio Astronomy, Bonn)

The most extreme phenomena in the Universe since the Big Bang are associated with explosive, transient astrophysical phenomena. The underlying physics of these events ranges from the release of gravitational potential energy as matter falls into black holes, to the explosive merger of two neutron stars and their associated electromagnetic and gravitational wave burst.

Radio emission from such events results from the spiralling of shock-accelerated, relativistic electrons around magnetic field lines, via the synchrotron process. The shock acceleration of the particles and compression and enhancement of the magnetic field result in turn from the supersonic outflow of matter from these transients, usually in the form of highly relativistic, collimated ‘jets’. Although having very large energy content, this synchrotron emission is usually unobservably faint at higher frequencies. Observations with radio telescopes are therefore the only way to study the kinetic output from such transient events, and have revealed it to be a fundamental and powerful channel for the dissipation of the released energy. A prime recent example is the relativistic jet, observed at radio wavelengths, from the neutron star merger and gravitational wave burst (LIGO) event GW170817, in which our team are heavily involved.

MeerKAT is the most powerful radio telescope in the southern hemisphere, and both Oxford and Bonn co-lead projects to study transients with the array over the next five years (via the ThunderKAT and TRAPUM projects). In addition, during this project the telescope will be upgraded with new high-frequency receivers, and expanded to a greater sensitivity and angular resolution, via direct investment from the Max Planck institute in Bonn. The successful applicant will be one of the first users of this extended MeerKAT, helping to commission it and using its upgraded sensitivity to study the radio universe in unprecedented detail. We are furthermore working at the cutting edge of software development for radio astronomy, and are looking to Machine Learning to dramatically improve our scientific analysis of the data. Major discoveries await!

Two projects are potentially available:

The first project involves the successful applicant working both at Oxford Astrophysics and the Max Planck Institute in Bonn, and will make use of the extended MeerKAT radio telescope array in South Africa. As a result, the student will spend at least one year of their studies based in Bonn, working in the relativistic astrophysics group there, and will be expected to make multiple visits to South Africa. In addition, there will be frequent additional travel to collaboration meetings and conferences.

The second project will investigate the application of Machine Learning techniques to the problems of imaging radio astronomical data, and also to the detection and classification of radio transients found in images. The new computational techniques developed will be applied to the data from the extended MeerKAT array, providing the student with early access to the world's most sensitive radio astronomical data. This may lead to a breakthrough in the way that interferometric imaging is processed, while in parallel leading to a guaranteed yield of exciting radio transient discoveries.