Quelltext der Seite 610 Pulsar observations with the Low Frequency Array

This lab course aims to teach the basics of radio astronomical data processing and its scientific uses using pulsar observations at 150\,MHz with the Low Frequency Array (LOFAR). You will learn how to select targets and plan observations with one of the most modern radio telescopes, as well as handle radio astronomical data to inspect properties of pulsars and the Milky Way.

From an observational standpoint, a pulsar is defined as a radio source that emits repeating sequences of regularly spaced pulses with periods of several milliseconds to seconds over a broad frequency range in the radio regime. Observations and theoretical models over the last decades have shown that the origin is a rotating neutron star. The pulsed characteristics of the emission originate from a displacement of the magnetic axes from the rotational axes of the neutron star generating a lighthouse effect. Neutron stars are known to have very strong magnetic fields with field strength in the range of 10^8-10^14 G. They are thought to form in core-collapse supernovae. The fraction of active pulsars is less than 1%. Albeit pulsars are interesting in themselves due to their extreme physical conditions, they can additionally be used as probes for the medium on the line-of-sight (LOS) to the observer.

Observations of a pulsar not only allow an investigation of the object itself, but also of the intervening medium. The interstellar medium (ISM) causes a dispersion (or delay) of the radio waves as a function of frequency. The radiation (of the pulses) at different frequencies thus take a different amount of time to traverse from the pulsar to the observer. This effect depends on the integrated electron density along the LOS. In cases where polarized emission is detectable from the pulsar an investigation of the intervening magnetic fields is also possible through the Faraday effect. This describes the frequency dependent rotation of the polarization vector in the presence of a magnetic field and charged particles. Utilizing both effects the observations taken during the lab, allow the determination of the integrated electron density and the average LOS component of the magnetic field of the Milky Way.

This lab course is divided into two parts separated by at least two weeks. The first part encompasses the selection and scheduling of observations while the second part consists of the reduction and analysis of the data taken. The data will be analysed to inspect the properties of the observed pulsars, their dispersion and rotation measures and finally determine from these values the average magnetic field strength of the Milky Way on the line-of-sight.