Pulsar scintillation studies with LOFAR. I. The census

Context. Interstellar scintillation (ISS) of pulsar emission can be used both as a probe of the ionised interstellar medium (IISM) and cause corruptions in pulsar timing experiments. Of particular interest are so-called scintillation arcs which can be used to measure time-variable interstellar scattering delays directly, potentially allowing high-precision improvements to timing precision. Aims. The primary aim of this study is to carry out the first sizeable and self-consistent census of diffractive pulsar scintillation and scintillation-arc detectability at low frequencies, as a primer for larger-scale IISM studies and pulsar-timing related propagation studies with the LOw-Frequency ARray (LOFAR) High Band Antennae (HBA). Results. In this initial set of 31 sources, 15 allow full determination of the scintillation properties; nine of these show detectable scintillation arcs at 120-180 MHz. Eight of the observed sources show unresolved scintillation; and the final eight don't display diffractive scintillation. Some correlation between scintillation detectability and pulsar brightness and dispersion measure is apparent, although no clear cut-off values can be determined. Our measurements across a large fractional bandwidth allow a meaningful test of the frequency scaling of scintillation parameters, uncorrupted by influences from refractive scintillation variations. Conclusions. Our results indicate the powerful advantage and great potential of ISS studies at low frequencies and the complex dependence of scintillation detectability on parameters like pulsar brightness and interstellar dispersion. This work provides the first installment of a larger-scale census and longer-term monitoring of interstellar scintillation effects at low frequencies.