nassp masters project 2016 university of the western cape

NASSP Masters Project 2016 University of the Western Cape

Dispersion measure variations in pulsarobservations with LOFAR

Supervisor: Maciej Serylak1,2 email: mserylak@gmail.comCo-supervisor: Aris Karastergiou3,4,1 email: aris@astro.ox.ac.uk1Department of Physics & Astronomy, University of the Western Cape2SKA South Africa3Oxford Astrophysics, University of Oxford4Department of Physics and Electronics, Rhodes University

Background

The interstellar medium (ISM) is the gaseous matter between the stars of a galaxy. As radio emission from pulsarspropagates through the ionized interstellar medium (ISM) it interacts with free electrons leading to observable prop-agation effects. One of these effects is dispersion. This effect is immediately obvious in frequency-resolved pulsesfrom radio pulsars: the pulses observed at lower radio frequencies arrive later at the telescope than their higher fre-quency counterparts (see Fig. 1). This delay is inversely proportional to the square of the observing frequency and theconstant of proportionality is called the Dispersion Measure (DM). By precise analysis of the DM and its temporalvariations one can get information about the ISM structure (see Fig. 1). The dispersive delay is much more pronouncedat the low observing frequencies of LOFAR - a radio telescope designed to operate at frequencies around 100 MHz.Low frequency observations allow to probe time-dependent changes in the ISM at very high precision and to improvemeasurements of contributions from higher-order dispersive terms, if these exist, thereby strongly constraining thegeneral ISM properties.

Figure 1: Left: Pulse dispersion. Dispersive delay seen in a pulsar observation done with LOFAR. Right: Dispersionmeasure variations for various radio telescopes (including LOFAR) with DM variation model plotted with the data.

Project Description

The project involves work with a large sample of pulsar observations taken with LOFAR radio telescope. The obser-vations are made with weekly cadence starting from 2013 and are still ongoing. The data reduction and analysis willbe made using readily available pulsar reduction tools (PSRCHIVE, TEMPO2). Prior knowledge of Linux operatingsystem is an advantage. The project will involve some programing in PYTHON and possibly in C. The work will bedone in the SKA Office in Pinelands and the necessary facilities will be provided.

Further Reading

Lorimer, D.R & Kramer, M. Handbook of Pulsar Astronomy, 2005, Cambridge University Press