Single pulse emission from PSR B0809+74 at 150 MHz using Polish LOFAR station

We report the observations of single pulse emission from the pulsar B0809+74 at 150 MHz using the Polish LOFAR station, PL-611. The three major phenomena of subpulse drifting, nulling, and mode changing associated with single pulse variations are prominently seen in these observations. The pulsar has a single-component conal profile and the single pulses are primarily in the 'normal' drift mode with periodicity (P$_{3}$) 11.1 ± 0.5 P for 96 per cent of the observing duration, while the shorter duration 'slow-drift' mode has P$_{3}$ = 15.7 ± 1.2 P. We were able to measure the phase behaviour associated with drifting from the fluctuation spectral analysis that showed identical linear phase variations across the pulse window for both modes despite their different periodic behaviour. Earlier studies reported that the transitions from the normal state to the slow-drift mode were preceded by the presence of nulling with typical durations of 5 to 10 periods. Our observations however seem to suggest that the transition to nulling follows shortly after the pulsar switches to the slow-drift mode and not at the boundary between the modes, with one instance of complete absence of nulling between mode switching. In addition, we also detected a second type of short-duration nulls not associated with the mode changing that showed quasi-periodic behaviour with periodicity PN ∼ 44 ± 7. The variety of features revealed in the single pulse sequence makes PSR B0809+74 an ideal candidate to understand the physical processes in the Partially Screened Gap dominated by non-dipolar magnetic fields

Time variation in the low-frequency spectrum of Vela-like pulsar B1800-21

We report the flux measurement of the Vela-like pulsar B1800−21 at the low radio frequency regime over multiple epochs spanning several years. The spectrum shows a turnover around the GHz frequency range and represents a typical example of gigahertz-peaked spectrum (GPS) pulsar. Our observations revealed that the pulsar spectrum show a significant evolution during the observing period with the low-frequency part of the spectrum becoming steeper, with a higher turnover frequency, for a period of several years before reverting back to the initial shape during the latest measurements. The spectral change over times spanning several years requires dense structures, with free electron densities around 1000–20 000 cm−3 and physical dimensions ∼220 au, in the interstellar medium (ISM) traversing across the pulsar line of sight. We look into the possible sites of such structures in the ISM and likely mechanisms particularly the thermal free–free absorption as possible explanations for the change

Finding the Ionospheric Fluctuations Reflection in the Pulsar Signals’ Characteristics Observed with LOFAR

Pulsars’ signals reaching the atmosphere can be considered being stable under certain assumptions. In such a case the ionosphere remains the main factor distorting signal from the extraterrestrial sources, particularly if we observe them at long radio waves. In this article we present the results of the analysis of relative peak flux changes for two selected pulsars: PSR J0332+5434 (B0329+54) and PSR J1509+5531 (B1508+55), observed with the long radio wave sensor (The PL612 Low Frequency Array (LOFAR) station in Bałdy), together with the analysis of Rate of TEC (ROT) parameter changes measured with the Global Navigation Satellite Systems (GNSS) sensor (IGS LAMA station (IGS: International GSSN Service)). The main objective of the work is to find if the rapid plasma density (observed with the Rate of Total Electron Content (TEC)) has a counterpart in the pulsar observation characteristics. This focuses the attention on ionosphere influence during pulsar investigations at low radio frequencies. Additionally, what was the aim of this work, our results give reasons for using pulsar signals from LOFAR together with GNSS data as multi instrumental ionosphere state probes. Our results show a clear anti-correlation between the ROT and the pulsar profile’s peak flux trends

Pulsar observations using the POLFAR stations

In this paper we present the current status of the pulsar observations conduct by Polish LOFAR stations. In particular we show that the single LOFAR station can provide observations that are of sufficient quality to provide useful scientific data. These can help us to better understand some of the phenomena related to the pulsar emission and the influence of the interstellar matter. In this paper we focus on the mode switching phenomenon and a single pulses analysis conducted for pulsar B0329+54. We find that the same spectral features are visible in both emission modes, so we conclude that the polar cap emission mechanism is the same in separated modes