Investigating astrophysical plasmas with pulsars using LOFAR and other telescopes

Pulsars are rapidly-rotating, highly-magnetised neutron stars that produce radio emission in their magnetospheres, which is detected as pulses on Earth. The focus of this thesis is observing pulsars as the means to study the properties of astrophysical plasmas that span many orders of magnitude in magnetic field strength (B) and scale. Chapter 1 provides an introduction to pulsars, their use as as probes of astrophysical plasmas, and our current knowledge of the Galactic magnetic field. Chapter 2 presents the numerous magnetospheric (B ~ 1012 G) emission characteristics of a mode-changing pulsar, PSR B0823+26, the mechanism behind which is not yet well understood. Using Low Frequency Array (LOFAR) observations, I report on the discovery that PSR B0823+26 has a weak and sporadically-emitting 'quiet' mode that is over 100 times weaker than that of the more regularly-emitting 'bright' mode. The transition between emission modes is concurrent across the range of frequencies observed and occurs within one rotational period (0.531 seconds). In Chapter 3 I review the practical methods for determining Faraday rotation measures (RMs) towards polarised sources, and collect the literature RMs measured towards pulsars and extragalactic (EG) sources, for the purpose of studying the Galactic magnetic field (GMF, B ~ μG). Chapter 4 describes the effect of the ionosphere on radio observations of astronomical sources. Observations of pulsars using LOFAR demonstrate the high accuracy of a code used to calculate the amount of ionospheric Faraday rotation towards a specific line-of-sight using publicly available, GPS-derived total electron content maps and the geomagnetic reference field (B ~ 0.5 G). I show that this technique can confidently determine some of the highest-precision ionosphere-corrected RMs towards pulsars ever achieved, towards more accurately measuring and monitoring the GMF. Chapter 5 presents new, or increased-accuracy, ionosphere-corrected RMs towards pulsars using polarisation observations with three different central radio frequencies. The RMs towards pulsars and EGs collected in Chapters 3 and 5 are used to reconstruct a map of the large-scale GMF using wavelet analysis, for which the additional RM data were beneficial. However, to more accurately reconstruct the three-dimensional GMF, more RMs and independent pulsar distances are required, especially towards the Galactic halo. Chapter 6 summarises this thesis and provides prospects for future related work

Multi-Wavelength Properties of the 2021 Periastron Passage of PSR B1259-63

PSR B1259-63 is a gamma-ray binary system hosting a radio pulsar orbiting around a O9.5Ve star, LS 2883, with a period of similar to 3.4 years. The interaction of the pulsar wind with the LS 2883 outflow leads to unpulsed broadband emission in the radio, X-ray, GeV, and TeV domains. One of the most unusual features of the system is an outburst of GeV energies around the periastron, during which the energy release substantially exceeds the spin down luminosity under the assumption of the isotropic emission. In this paper, we present the first results of a recent multi-wavelength campaign (radio, optical, and X-ray bands) accompanied by the analysis of publicly available GeV Fermi/LAT data. The campaign covered a period of more than 100 days around the 2021 periastron and revealed substantial differences from previously observed passages. We report a major delay of the GeV flare, weaker X-ray flux during the peaks, which are typically attributed to the times when the pulsar crosses the disk, and the appearance of a third X-ray peak never observed before. We argue that these features are consistent with the emission cone model proposed by us previously, in the case of a sparser and clumpier disk of the Be star

An ultra-wide bandwidth (704 to 4 032 MHz) receiver for the Parkes radio telescope

We describe an ultra-wide-bandwidth, low-frequency receiver recently installed on the Parkes radio telescope. The receiver system provides continuous frequency coverage from 704 to 4032 MHz. For much of the band ( ${∼}60$ ), the system temperature is approximately 22 K and the receiver system remains in a linear regime even in the presence of strong mobile phone transmissions. We discuss the scientific and technical aspects of the new receiver, including its astronomical objectives, as well as the feed, receiver, digitiser, and signal processor design. We describe the pipeline routines that form the archive-ready data products and how those data files can be accessed from the archives. The system performance is quantified, including the system noise and linearity, beam shape, antenna efficiency, polarisation calibration, and timing stability

Using low-frequency pulsar observations to study the 3-D structure of the Galactic magnetic field

© 2018 International Astronomical Union. The Galactic magnetic field (GMF) plays a role in many astrophysical processes and is a significant foreground to cosmological signals, such as the Epoch of Reionization (EoR), but is not yet well understood. Dispersion and Faraday rotation measurements (DMs and RMs, respectively) towards a large number of pulsars provide an efficient method to probe the three-dimensional structure of the GMF. Low-frequency polarisation observations with large fractional bandwidth can be used to measure precise DMs and RMs. This is demonstrated by a catalogue of RMs (corrected for ionospheric Faraday rotation) from the Low Frequency Array (LOFAR), with a growing complementary catalogue in the southern hemisphere from the Murchison Widefield Array (MWA). These data further our knowledge of the three-dimensional GMF, particularly towards the Galactic halo. Recently constructed or upgraded pathfinder and precursor telescopes, such as LOFAR and the MWA, have reinvigorated low-frequency science and represent progress towards the construction of the Square Kilometre Array (SKA), which will make significant advancements in studies of astrophysical magnetic fields in the future. A key science driver for the SKA-Low is to study the EoR, for which pulsar and polarisation data can provide valuable insights in terms of Galactic foreground conditions

A Census of Southern Pulsars at 185 MHz

The Murchison Widefield Array, and its recently developed Voltage Capture System, facilitates extending the low-frequency range of pulsar observations at high-time and -frequency resolution in the Southern Hemisphere, providing further information about pulsars and the ISM. We present the results of an initial time-resolved census of known pulsars using the Murchison Widefield Array. To significantly reduce the processing load, we incoherently sum the detected powers from the 128 Murchison Widefield Array tiles, which yields ~10% of the attainable sensitivity of the coherent sum. This preserves the large field-of-view (~450 deg 2 at 185 MHz), allowing multiple pulsars to be observed simultaneously. We developed a WIde-field Pulsar Pipeline that processes the data from each observation and automatically folds every known pulsar located within the beam. We have detected 50 pulsars to date, 6 of which are millisecond pulsars. This is consistent with our expectation, given the telescope sensitivity and the sky coverage of the processed data (~17 000 deg 2 ). For 10 pulsars, we present the lowest frequency detections published. For a subset of the pulsars, we present multi-frequency pulse profiles by combining our data with published profiles from other telescopes. Since the Murchison Widefield Array is a low-frequency precursor to the Square Kilometre Array, we use our census results to forecast that a survey using the low-frequency component of the Square Kilometre Array Phase 1 can potentially detect around 9 400 pulsars

Multi-Wavelength Properties of the 2021 Periastron Passage of PSR B1259-63

PSR B1259-63 is a gamma-ray binary system hosting a radio pulsar orbiting around a O9.5Ve star, LS 2883, with a period of ∼3.4 years. The interaction of the pulsar wind with the LS 2883 outflow leads to unpulsed broadband emission in the radio, X-ray, GeV, and TeV domains. One of the most unusual features of the system is an outburst of GeV energies around the periastron, during which the energy release substantially exceeds the spin down luminosity under the assumption of the isotropic emission. In this paper, we present the first results of a recent multi-wavelength campaign (radio, optical, and X-ray bands) accompanied by the analysis of publicly available GeV Fermi/LAT data. The campaign covered a period of more than 100 days around the 2021 periastron and revealed substantial differences from previously observed passages. We report a major delay of the GeV flare, weaker X-ray flux during the peaks, which are typically attributed to the times when the pulsar crosses the disk, and the appearance of a third X-ray peak never observed before. We argue that these features are consistent with the emission cone model proposed by us previously, in the case of a sparser and clumpier disk of the Be star

Hunting for Radio Emission from the Intermittent Pulsar J1107-5907 at Low Frequencies

Rare intermittent pulsars pose some of the most challenging questions surrounding the pulsar emission mechanism, but typically have relatively minimal low-frequency (?300 MHz) coverage. We present the first low-frequency detection of the intermittent pulsar J1107-5907 with the Murchison Widefield Array (MWA) at 154 MHz and the simultaneous detection from the recently upgraded Molonglo Observatory Synthesis Telescope (UTMOST) at 835 MHz, as part of an ongoing observing campaign. During a 30 minute simultaneous observation, we detected the pulsar in its bright emission state for approximately 15 minutes, where 86 and 283 pulses were detected above a signal-to-noise threshold of 6 with the MWA and UTMOST, respectively. Of the detected pulses, 51 had counterparts at both frequencies and exhibited steep spectral indices for both the bright main pulse component and the precursor component. We find that the bright state pulse energy distribution is best parameterized by a log-normal distribution at both frequencies, contrary to previous results that suggested a power law distribution. Further low-frequency observations are required in order to explore in detail aspects such as pulse-to-pulse variability and intensity modulations, as well as to better constrain the signal propagation effects due to the interstellar medium and intermittency characteristics at these frequencies. The spectral index, extended profile emission covering a large fraction of pulse longitude, and the broadband intermittency of PSR J1107-5907 suggest that future low-frequency pulsar searches - for instance, those planned with SKA-Low - will be in an excellent position to find and investigate new pulsars of this type

The economic balance of dealing with the concept of Kočičí vrch-Ležáky stone quarry in relation to variant plans of extraction and deposition

Import 30/07/2007Prezenční542 - Institut hornického inženýrství a bezpečnost