Observations of interstellar scattering of six pulsars using Polish LOFAR station PL611

Abstract

ABSTRACT We present the preliminary results of 4 yr of observations of the scattering of pulsar radiation in the interstellar medium using the Low Frequency Array (LOFAR) PL611 station located in Lazy near Krakow. In this work we show the initial results for six pulsars from our observing campaign. We used the HBA antennas of the station, with a central frequency of 154 MHz and a 72 MHz bandwidth and we were able to detect the frequency-dependent change in the pulse profiles. Splitting the bandwidth into a number of separate sub-bands we obtained independent scatter time estimates, which allowed for the estimation of the scattering frequency scaling slope for each individual observation. Our project has been accumulating data for more than 4 yr and as a result we are in a position to study the time variability of the scattering parameters over this period. We detected significant changes in the scatter time and its frequency scaling for at least two of pulsars. The average values of the frequency scaling index for the six pulsars selected for this work are below the range of values predicted by the simple thin screen model of interstellar scattering. This is in accordance with previous results shown for both higher dispersion measure pulsars observed in the past, as well as the more recent LOFAR observations and other projects similar in the observing frequency. We also discuss the advantages of using individual LOFAR stations (or similar instruments) for this kind of research.