MSc Projects 2004
Pulsars provide the nearest thing to a physicist's dream come true. Being the end-point of stellar evolution, they are densest bodies next to black holes and give us an insight into the most extreme physical conditions of matter density, pressure and magnetic field observable by man. They also provide the most precise clocks known to humankind for undertaking unique experiments of gravitation and general relativity. Furthermore, they can be used as probes of the distribution of ionised material and magnetic field in the Galaxy with a precision which nothing else can. We use the telescopes at Jodrell Bank, Parkes (Australia) and Arecibo (Puerto Rico) in this work and frequently travel to the foreign instruments to make observations. The pulsar group at Jodrell Bank are arguably the most productive in the world in this area and have discovered more than three-quarters of the known population of these elusive and fascinating objects.
There are several main active areas of research in the general area of pulsar astronomy which would support projects which would be ideal for students, starting in September 2004. We outline four of these below. Portions of a further three projects listed on the PhD page may also be suitable for MSc students. Links to these projects can be found at the bottom of this page.
Modelling the Binary Pulsar Population in our Galaxy
Understanding how pulsars are born, evolve and ultimately end their lives is a fascinating subject which utilises a number of areas of astrophysics: stellar structure and evolution, orbital mechanics and binary evolution, neutron star kinematics, accretion physics etc. Since over half of all normal stars are in binary systems, the evolution of binary stars plays a key role in understanding the different types of pulsars we observe. A simplified version of the various channels of binary pulsar evolution is shown in the cartoon below.
The aim of this project is to develop a Monte Carlo simulation to follow in detail the above evolutionary paths and predict the various fractions of pulsar populations that we observe. The basis for this work will, initially be the comprehensive framework described in this paper and the first task will be to reproduce the results of this work. With this simulation in hand, the student will be able to explore the various impacts that initial conditions have on the resulting simulated populations. The second part of the project will be to extend this model to take account of known observational selection effects which bias the underlying sample in order to make testable predictions on the number of binary systems we observe. A student, preferably competent in C programming, is sought to take up this project which will serve as an excellent introduction to Monte Carlo simulations, population modelling and statistical/numerical techniques. For further information, please contact Dunc Lorimer (drl@jb.man.ac.uk)
Searching for long-period pulsars with the GMRT
Of the roughly 1600 pulsars discovered to date, only 30 have periods longer than 3 seconds, with the slowest spinning pulsar having a period of 8.5 seconds. For many years, it was believed that all of these long-period pulsars were old pulsars who were slowing down and reaching the end of their radio lifetimes. Recently, however, we have discovered a new class of radio pulsars which have long periods but appear to be very young, with ultra-high magnetic fields. These pulsars have very similar spin parameters to the luminous high-energy sources known as anomalous X-ray pulsars and soft gamma-ray repeaters, often referred to collectively as "magnetars".
Finding more long-period pulsars is important for several reasons. While the first radio pulsar was discovered roughly 35 years ago, our knowledge of how pulsars emit radio waves is still woefully inadequate. A more complete sample of older, slow pulsars is important for determining when the pulsar radio emission "turns off" and for understanding the origin of the pulsar radio emission itself. Phenomenon such as subpulse drifting and nulling, which are often seen in long-periods pulsars, offer vital clues to the pulsar emission mechanism. Finding more high magnetic field radio pulsars is crucial for understanding the conditions under which a young neutron star manifests itself as a radio pulsar or magnetar and, again, for constraining the pulsar radio emission mechanism itself. Our recent discoveries of radio pulsars with high magnetic fields has already forced theorists to rethink their accepted theories for pulsar radio emission; finding more of these objects may constrain the allowed emission mechanisms even further.
Why are there so few long-period pulsars currently known? This is due, at least in part, to selection effects inherent in almost all previous pulsar surveys. Many of these surveys employed high-pass filtering, increasing robustness to radio interference but decreasing sensitivity to long-period signals. In many previous searches, software cutoffs to signals above 3-5 seconds have also been employed. Furthermore, long-period pulsars tend to have narrower emission beams, making it less likely that one will intersect our line of sight.
Our recent
discovery
of a radio pulsar with magnetar-like
spin-properties blurs the distinction between radio pulsars and
magnetars and shows that there seems to be no compelling argument why
magnetars cannot be radio emitters. Therefore, in order to better
understand the pulsar emission mechanism, the radiation process in
magnetars and the relationship between canonical radio pulsars and
magnetars, we have performed a sensitive search for periodic and
a-periodic radio emission from magnetars using the Parkes radio
telescope in Australia. We used a special radio receiver at the
telescope combined with some dedicated hardware, which allowed us to
do a unique search for radio emission of these objects. As we might
expect the radio emission to be a-periodic or bursty, we chose this
set-up in order to be able to distinguish real signals such as these
from radio frequency interference.
The student would analyse the observed data which have the potential to
shed light on the possible physical and/or evolutionary relationship
between radio pulsars, radio-quiet pulsars and magnetars.
For further information, please
contact Michael Kramer (mkramer@jb.man.ac.uk)
While individual pulses emitted by radio pulsars are often very
different from one another, the computation of the average pulse shape
based on a few hundred pulses or so, results in a very stable pulse
profile. This is due to the fact that this profile is mostly
determined by geometry, i.e. the orientation of the pulsar's spin and
magnetic axes relative to Earth. It is the stability of the pulsar
profile that allows us to use pulsars as accurate cosmic clocks.
However, if the geometry were changing, then would expect changes in
the pulsar profile, which would also be visible in the timing of the
pulsar as a clock (see figure).
A reason for a change in geometry could be a free precession of the pulsar.
However, free precession is not expected in pulsar as they have a
liquid super-fluid core. Nevertheless, we discovered in Jodrell Bank a
pulsar which seem to do exactly that - freely precessing in space
causing a periodic change in the pulse profile. Hence, it is important
to find out as to whether this pulsar is unique, or whether the phenomenon
can also be observed in other pulsars as well. Jodrell Bank's timing
program is the most extensive in the world and offers exactly the
kind of data necessary to perform such a study. The student working
on this project would study the available data to indentify possible
profile changes that could be attributed to free precession.
For further information, please
contact Michael Kramer (mkramer@jb.man.ac.uk) or Andrew Lyne (agl@jb.man.ac.uk)
This project is described in full
here.
Part of this project could be tackled as a self-contained MSc thesis.
Please contact Andrew Lyne (agl@jb.man.ac.uk) or Maura McLaughlin
(mclaughl@jb.man.ac.uk) for details.
This project is described in full
here.
Part of this project could be tackled as a self-contained MSc thesis.
Please contact Michael Kramer
(mkramer@jb.man.ac.uk) or Maura McLaughlin
(mclaughl@jb.man.ac.uk) for details.
A search for radio emission from Magnetars
Multi-wavelength studies of a massive binary pulsar
Probing the Interstellar Medium using Pulsars