Parkes Radio Telescope Research Articles

Expanded Capability of the Breakthrough Listen Parkes Data Recorder for Observations with the UWL Receiver

Abstract The ultra-wideband low (UWL) receiver is a new feed for the Parkes telescope, which covers the combined bandwidth of four previously installed receivers. In order to use the UWL for technosignature observations, several updates and upgrades were made on the Breakthrough Listen Parkes Data Recorder (BLPDR). This Research Note summarizes BLPDR hardware upgrades and new capacity for technosignature observations with the UWL receiver.

Giant molecular cloud formation at the interface of colliding supershells in the large magellanic cloud

ABSTRACT We investigate the H i envelope of the young, massive GMCs in the star-forming regions N48 and N49, which are located within the high column density H i ridge between two kpc-scale supergiant shells, LMC 4 and LMC 5. New long-baseline H i 21 cm line observations with the Australia Telescope Compact Array (ATCA) were combined with archival shorter baseline data and single dish data from the Parkes telescope, for a final synthesized beam size of 24.75 arcsec by 20.48 arcsec, which corresponds to a spatial resolution of ∼6 pc in the LMC. It is newly revealed that the H i gas is highly filamentary and that the molecular clumps are distributed along filamentary H i features. In total 39 filamentary features are identified and their typical width is ∼21 (8–49) [pc]. We propose a scenario in which the GMCs were formed via gravitational instabilities in atomic gas which was initially accumulated by the two shells and then further compressed by their collision. This suggests that GMC formation involves the filamentary nature of the atomic medium.

Effects of periodicity in observation scheduling on parameter estimation of pulsar glitches

ABSTRACT In certain pulsar timing experiments, where observations are scheduled approximately periodically (e.g. daily), timing models with significantly different frequencies (including but not limited to glitch models with different frequency increments) return near-equivalent timing residuals. The average scheduling aperiodicity divided by the phase error due to time-of-arrival uncertainties is a useful indicator when the degeneracy is important. Synthetic data are used to explore the effect of this degeneracy systematically. It is found that phase-coherent tempo2 or temponest-based approaches are biased sometimes towards reporting small glitch sizes regardless of the true glitch size. Local estimates of the spin frequency alleviate this bias. A hidden Markov model is free from bias towards small glitches and announces explicitly the existence of multiple glitch solutions but sometimes fails to recover the correct glitch size. Two glitches in the UTMOST public data release are reassessed, one in PSR J1709−4429 at MJD 58178 and the other in PSR J1452−6036 at MJD 58600. The estimated fractional frequency jump in PSR J1709−4429 is revised upward from Δf/f = (54.6 ± 1.0) × 10−9 to (2432.2 ± 0.1) × 10−9 with the aid of additional data from the Parkes radio telescope. We find that the available UTMOST data for PSR J1452−6036 are consistent with Δf/f = 270 × 10−9 + N/(fT) with N = 0, 1, and 2, where $T \approx 1\, \text{sidereal day}$ is the observation scheduling period. Data from the Parkes radio telescope can be included, and the N = 0 case is selected unambiguously with a combined data set.

A polarization census of bright pulsars using the ultrawideband receiver on the Parkes radio telescope

ABSTRACT We present high signal-to-noise ratio, full polarization pulse profiles for 40 bright, ‘slowly’ rotating (non-recycled) pulsars using the new ultrawideband low-frequency (UWL; 704–4032 MHz) receiver on the Parkes radio telescope. We obtain updated and accurate interstellar medium parameters towards these pulsars (dispersion measures and Faraday rotation measures), and reveal Faraday dispersion towards PSR J1721–3532 caused by interstellar scattering. We find general trends in the pulse profiles including decreasing fractional linear polarization and increasing degree of circular polarization with increasing frequency, consistent with previous studies, while also revealing new features and frequency evolution. This demonstrates results that can be obtained using UWL monitoring observations of slow pulsars, which are valuable for improving our understanding of pulsar emission and the intervening interstellar medium. The calibrated data products are publicly available.

Constraints on wide-band radiative changes after a glitch in PSR J1452–6036

ABSTRACT We present high-sensitivity, wide-band observations (704–4032 MHz) of the young to middle-aged radio pulsar J1452–6036, taken at multiple epochs before and, serendipitously, shortly after a glitch occurred on 2019 April 27. We obtained the data using the new ultra-wide-bandwidth low-frequency (UWL) receiver at the Parkes radio telescope, and we used Markov chain Monte Carlo techniques to estimate the glitch parameters robustly. The data from our third observing session began 3 h after the best-fitting glitch epoch, which we constrained to within ∼4 min. The glitch was of intermediate size, with a fractional change in spin frequency of 270.52(3) × 10−9. We measured no significant change in spin-down rate and found no evidence for rapidly decaying glitch components. We systematically investigated whether the glitch affected any radiative parameters of the pulsar and found that its spectral index, spectral shape, polarization fractions, and rotation measure stayed constant within the uncertainties across the glitch epoch. However, its pulse-averaged flux density increased significantly by about 10 per cent in the post-glitch epoch and decayed slightly before our fourth observation a day later. We show that the increase was unlikely caused by calibration issues. While we cannot exclude that it was due to refractive interstellar scintillation, it is hard to reconcile with refractive effects. The chance coincidence probability of the flux density increase and the glitch event is low. Finally, we present the evolution of the pulsar’s pulse profile across the band. The morphology of its polarimetric pulse profile stayed unaffected to a precision of better than 2 per cent.

An HI intensity mapping survey with a Phased Array Feed

We report results from a neutral hydrogen (H i) intensity mapping survey conducted with a Phased Array Feed (PAF) on the Parkes telescope. The survey was designed to cover ∼ 380 deg2 over the redshift range 0.3 < z < 1 (a volume of ∼ 1.5 Gpc3) in four fields covered by the WiggleZ Dark Energy Survey. The results presented here target a narrow redshift range of 0.73 < z < 0.78 where the effect of radio frequency interference (RFI) was less problematic. The data reduction and simulation pipeline was described, with an emphasis on flagging of RFI and correction for signal loss in the data reduction process, particularly due to the foreground subtraction methodology. A cross-correlation signal was detected between the H i intensity maps and the WiggleZ redshift data, with a mean amplitude of ⟨ΔT b δ opt⟩ = 1.32 ± 0.42 mK (statistical errors only). A future Parkes cryogenic PAF is expected to detect the cross-correlation signal with higher accuracy than previously possible and allow measurement of the cosmic H i density at redshifts up to unity.

The physics of fast radio bursts

In 2007, a very bright radio pulse was identified in the archival data of the Parkes Telescope in Australia, marking the beginning of a new research branch in astrophysics. In 2013, this kind of millisecond bursts with extremely high brightness temperature takes a unified name, fast radio burst (FRB). Over the first few years, FRBs seemed very mysterious because the sample of known events was limited. With the improvement of instruments over the last five years, hundreds of new FRBs have been discovered. The field is now undergoing a revolution and understanding of FRB has rapidly increased as new observational data increasingly accumulates. In this review, we will summarize the basic physics of FRBs and discuss the current research progress in this area. We have tried to cover a wide range of FRB topics, including the observational property, propagation effect, population study, radiation mechanism, source model, and application in cosmology. A framework based on the latest observational facts is now under construction. In the near future, this exciting field is expected to make significant breakthroughs.

A Multiwavelength Survey of Wolf–Rayet Nebulae in the Large Magellanic Cloud

Abstract Surveys of Wolf–Rayet (WR) stars in the Large Magellanic Cloud (LMC) have yielded a fairly complete catalog of 154 known stars. We have conducted a comprehensive, multiwavelength study of the interstellar/circumstellar environments of WR stars, using the Magellanic Cloud Emission Line Survey images in the Hα, [O iii], and [S ii] lines; Spitzer Space Telescope 8 and 24 μm images; Blanco 4 m Telescope Hα CCD images; and Australian Telescope Compact Array + Parkes Telescope H i data cube of the LMC. We have also examined whether the WR stars are in OB associations, classified the H ii environments of WR stars, and used this information to qualitatively assess the WR stars’ evolutionary stages. The 30 Dor giant H ii region has active star formation and hosts young massive clusters, thus we have made statistical analyses for 30 Dor and the rest of the LMC both separately and altogether. Due to the presence of massive young clusters, the WR population in 30 Dor is quite different from that from elsewhere in the LMC. We find small bubbles (&lt;50 pc diameter) around ∼12% of WR stars in the LMC, most of which are WN stars and not in OB associations. The scarcity of small WR bubbles is discussed. Spectroscopic analyses of abundances are needed to determine whether the small WR bubbles contain interstellar medium or circumstellar medium. Implications of the statistics of interstellar environments and OB associations around WR stars are discussed. Multiwavelength images of each LMC WR star are presented.

Two years of pulsar observations with the ultra-wide-band receiver on the Parkes radio telescope

ABSTRACT The major programme for observing young, non-recycled pulsars with the Parkes telescope has transitioned from a narrow-band system to an ultra-wide-band system capable of observing between 704 and 4032 MHz. We report here on the initial 2 yr of observations with this receiver. Results include dispersion measure (DM) and Faraday rotation measure (RM) variability with time, determined with higher precision than hitherto, flux density measurements and the discovery of several nulling and mode changing pulsars. PSR J1703−4851 is shown to be one of a small subclass of pulsars that has a weak and a strong mode which alternate rapidly in time. PSR J1114−6100 has the fourth highest |RM| of any known pulsar despite its location far from the Galactic Centre. PSR J1825−1446 shows variations in both DM and RM likely due to its motion behind a foreground supernova remnant.

Constraining the fast radio burst properties using the joint distributions of dispersion measure and fluence of the events detected at Parkes, ASKAP, CHIME, and UTMOST

ABSTRACT The Parkes, ASKAP, CHIME, and UTMOST telescopes, which have all detected fast radio bursts (FRBs), each works at a different frequency and has a different detection criteria. Using simulations, we have combined the constraints from all four telescopes to identify an allowed range of model parameters $(\alpha , \overline{E}_{33})$ for the FRB source population. Here, α is the spectral index and $\overline{E}_{33}$ is the mean FRB energy in units of $10^{33} \, {\rm J}$ across a 2128–2848 MHz band in the FRB rest frame. We have considered several different FRB energy distributions, and also different scenarios for the scattering pulse broadening, the event rate density variation with z and the host dispersion measure (DM). We find that in all cases, the common allowed region includes the range −3.9 ≤ α ≤ −1.3 and $0.42\le \overline{E}_{33}\le 1$. In all case, large values α &amp;gt; 4 and $\overline{E}_{33} \gt 60$ are ruled out. Considering the allowed $(\alpha , \overline{E}_{33})$ parameter range, we predict that CHIME is unlikely to detect an FRB with extragalactic dispersion measure (DMEx) exceeding $3700\, {\rm pc\, cm}^{-3}$. A substantially larger DMEx in the large FRB sample anticipated from CHIME would falsify the assumptions of the present analysis. Our analysis is expected to yield tighter parameter constraints with the advent of more FRB data.

Searching for gravitational-wave bursts from cosmic string cusps with the Parkes Pulsar Timing Array

ABSTRACT Cosmic strings are potential gravitational-wave (GW) sources that can be probed by pulsar timing arrays (PTAs). In this work we develop a detection algorithm for a GW burst from a cusp on a cosmic string, and apply it to Parkes PTA data. We find four events with a false alarm probability less than 1 per cent. However further investigation shows that all of these are likely to be spurious. As there are no convincing detections we place upper limits on the GW amplitude for different event durations. From these bounds we place limits on the cosmic string tension of Gμ ∼ 10−5, and highlight that this bound is independent from those obtained using other techniques. We discuss the physical implications of our results and the prospect of probing cosmic strings in the era of Square Kilometre Array.

Radio pulsations from the γ-ray millisecond pulsar PSR J2039–5617

ABSTRACT The predicted nature of the candidate redback pulsar 3FGL J2039.6–5618 was recently confirmed by the discovery of γ-ray millisecond pulsations (Clark et al., hereafter Paper I), which identify this γ-ray source as PSR J2039–5617. We observed this object with the Parkes radio telescope in 2016 and 2019. We detect radio pulsations at 1.4 and 3.1 GHz, at the 2.6 ms period discovered in γ-rays, and also at 0.7 GHz in one 2015 archival observation. In all bands, the radio pulse profile is characterized by a single relatively broad peak which leads the main γ-ray peak. At 1.4 GHz, we found clear evidence of eclipses of the radio signal for about half of the orbit, a characteristic phenomenon in redback systems, which we associate with the presence of intra-binary gas. From the dispersion measure of 24.57 ± 0.03 pc cm−3, we derive a pulsar distance of 0.9 ± 0.2 or 1.7 ± 0.7 kpc, depending on the assumed Galactic electron density model. The modelling of the radio and γ-ray light curves leads to an independent determination of the orbital inclination, and to a determination of the pulsar mass, qualitatively consistent to the results in Paper I.

Identifying and mitigating noise sources in precision pulsar timing data sets

ABSTRACT Pulsar timing array projects measure the pulse arrival times of millisecond pulsars for the primary purpose of detecting nanohertz-frequency gravitational waves. The measurements include contributions from a number of astrophysical and instrumental processes, which can either be deterministic or stochastic. It is necessary to develop robust statistical and physical models for these noise processes because incorrect models diminish sensitivity and may cause a spurious gravitational wave detection. Here we characterize noise processes for the 26 pulsars in the second data release of the Parkes Pulsar Timing Array using Bayesian inference. In addition to well-studied noise sources found previously in pulsar timing array data sets such as achromatic timing noise and dispersion measure variations, we identify new noise sources including time-correlated chromatic noise that we attribute to variations in pulse scattering. We also identify ‘exponential dip’ events in four pulsars, which we attribute to magnetospheric effects as evidenced by pulse profile shape changes observed for three of the pulsars. This includes an event in PSR J1713+0747, which had previously been attributed to interstellar propagation. We present noise models to be used in searches for gravitational waves. We outline a robust methodology to evaluate the performance of noise models and identify unknown signals in the data. The detection of variations in pulse profiles highlights the need to develop efficient profile domain timing methods.

The neutral hydrogen distribution in large-scale haloes from 21-cm intensity maps

ABSTRACT We detect the neutral hydrogen (H i) radial brightness temperature profile in large-scale haloes by stacking 48 430 galaxies selected from the 2dFGRS catalogue on to a set of 21-cm intensity maps obtained with the Parkes radio telescope, spanning a total area of ∼1300 deg2 on the sky and covering the redshift range 0.06 ≲ z ≲ 0.10. Maps are obtained by removing both 10 and 20 foreground modes in the principal component analysis. We perform the stack at the map level and extract the profile from a circularly symmetrized version of the halo emission. We detect the H i halo emission with the significance 12.5σ for the 10-mode and 13.5σ for the 20-mode removed maps at the profile peak. We jointly fit for the observed halo mass Mv and the normalization $c_{0,\rm H\, \small{I}}$ for the H i concentration parameter against the reconstructed profiles, using functional forms for the H i halo abundance proposed in the literature. We find $\log _{10}{(M_{\rm v}/\text{M}_{\odot })}= 16.1^{+0.1}_{-0.2}$, $c_{0,\rm H\, \small{I}}=3.5^{+0.7}_{-1.0}$ for the 10-mode and $\log _{10}{(M_{\rm v}/\text{M}_{\odot })}= 16.5^{+0.1}_{-0.2}$, $c_{0,\rm H\, \small{I}}=5.3^{+1.1}_{-1.7}$ for the 20-mode removed maps. These estimates show the detection of the integrated contribution from multiple galaxies located inside very massive haloes. We also consider subsamples of 13 979 central and 34 361 satellite 2dF galaxies separately, and obtain marginal differences suggesting satellite galaxies are H i-richer. This work shows for the first time the feasibility of testing theoretical models for the H i halo content directly on profiles extracted from 21-cm maps and opens future possibilities for exploiting upcoming H i intensity-mapping data.

Search for ultralight scalar dark matter with NANOGrav pulsar timing arrays

An ultralight scalar field is a candidate for the dark matter. The ultralight scalar dark matter with mass around 10−23 eV induces oscillations of the pulse arrival time in the sensitive frequency range of the pulsar timing arrays. We search for the ultralight scalar dark matter using the North American Nanohertz Observatory for Gravitational Waves 11-year Data Set. We give the 95% confidence upper limit for the signal induced by the ultralight scalar dark matter. In comparison with the published Bayesian upper limits on the amplitude of the ultralight scalar dark matter obtained by Bayesian analysis using the Parkes Pulsar Timing Array 12-year data set (Porayko et al. 2018), we find three times stronger upper limit in the frequency range from 10−8.34 to 10−8.19 Hz which corresponds to the mass range from 9.45×10−24 to 1.34×10−23 eV. In terms of the energy density of the dark matter, we find that the energy density near the Earth is less than 7 GeV/cm3 in the range from 10−8.55 to 10−8.01 Hz (from 5.83×10−24 to 2.02×10−23 eV). The strongest upper limit on the energy density is given by 2 GeV/cm3 at a frequency 10−8.28 Hz (corresponding to a mass 1.09×10−23 eV). We find that the signal of the ultralight scalar dark matter is strongly covariant with the solar system ephemeris effect. Also, we reveal that the model of the solar system ephemeris effect prefers parameters which are contrary to the expectation that noise will be reduced on all pulsars.

The SUrvey for pulsars and extragalactic radio bursts V: recent discoveries and full timing solutions

ABSTRACT The SUrvey for Pulsars and Extragalactic Radio Bursts ran from 2014 April to 2019 August, covering a large fraction of the Southern hemisphere at mid- to high-galactic latitudes and consisting of 9-min pointings taken with the 20-cm multibeam receiver on the Parkes Radio Telescope. Data up to 2017 September 21 have been searched using standard Fourier techniques, single-pulse searches, and Fast Folding Algorithm searches. We present 19 new discoveries, bringing the total to 27 discoveries in the programme, and we report the results of follow-up timing observations at Parkes for 26 of these pulsars, including the millisecond pulsar PSR J1421−4409; the faint, highly modulated, slow pulsar PSR J1646−1910; and the nulling pulsar PSR J1337−4441. We present new timing solutions for 23 pulsars, and we report flux densities, modulation indices, and polarization properties.

Pulsar polarimetry with the Parkes ultra-wideband receiver

ABSTRACT Pulsar radio emission and its polarization are observed to evolve with frequency. This frequency dependence is key to the emission mechanism and the structure of the radio beam. With the new ultra-wideband receiver (UWL) on the Parkes radio telescope we are able, for the first time, to observe how pulsar profiles evolve over a broad continuous bandwidth of 700–4000 MHz. We describe here a technique for processing broad-band polarimetric observations to establish a meaningful alignment and visualize the data across the band. We apply this to observations of PSRs J1056–6258 and J1359–6038, chosen due to previously unresolved questions about the frequency evolution of their emission. Application of our technique reveals that it is possible to align the polarization position angle (PA) across a broad frequency range when constrained to applying only corrections for dispersion and Faraday rotation to do so. However, this does not correspond to aligned intensity profiles for these two sources. We find that it is possible to convert these misalignments into emission height range estimates that are consistent with published and simulated values, suggesting that they can be attributed to relativistic effects in the magnetosphere. We discuss this work in the context of the radio beam structure and prepare the ground for a wider study of pulsar emission using broad-band polarimetric data.

Spectropolarimetric Properties of Swift J1818.0–1607: A 1.4 s Radio Magnetar

Abstract The soft-gamma repeater Swift J1818.0−1607 is only the fifth magnetar found to exhibit pulsed radio emission. Using the Ultra-Wideband Low receiver system of the Parkes radio telescope, we conducted a 3 hr observation of Swift J1818.0−1607. Folding the data at a rotation period of P = 1.363 s, we obtained wideband polarization profiles and flux density measurements covering radio frequencies between 704 and 4032 MHz. After measuring, and then correcting for the pulsar’s rotation measure of 1442.0 ± 0.2 rad m−2, we find the radio profile is between 80% and 100% linearly polarized across the wide observing band, with a small amount of depolarization at low frequencies that we ascribe to scatter broadening. We also measure a steep spectral index of across our large frequency range, a significant deviation from the flat or inverted spectra often associated with radio-loud magnetars. The steep spectrum and temporal rise in flux density bears some resemblance to the behavior of the magnetar-like, rotation-powered pulsar PSR J1119−6127. This leads us to speculate that Swift J1818.0−1607 may represent an additional link between rotation-powered pulsars and magnetars.

An in-depth investigation of 11 pulsars discovered by FAST

ABSTRACT We present timing solutions and analyses of 11 pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These pulsars were discovered using an ultrawide bandwidth receiver in drift-scan observations made during the commissioning phase of FAST, and were then confirmed and timed using the 64-m Parkes Radio Telescope. Each pulsar has been observed over a span of at least one year. Highlighted discoveries include PSR J0344−0901, which displays mode-changing behaviour and may belong to the class of so-called swooshing pulsars (alongside PSRs B0919+06 and B1859+07); PSR J0803−0942, whose emission is almost completely linearly polarized; and PSRs J1900−0134 and J1945+1211, whose well-defined polarization angle curves place stringent constraints on their emission geometry. We further discuss the detectability of these pulsars by earlier surveys, and highlight lessons learned from our work in carrying out confirmation and monitoring observations of pulsars discovered by a highly sensitive telescope, many of which may be applicable to next-generation pulsar surveys. This paper marks one of the first major releases of FAST-discovered pulsars, and paves the way for future discoveries anticipated from the Commensal Radio Astronomy FAST Survey.

Is GRB 110715A the Progenitor of FRB 171209?

Abstract The physical origin of fast radio bursts (FRBs) is unknown. Young magnetars born from gamma-ray bursts (GRBs) have been suggested as a possible central engine of FRBs. We test such a hypothesis by systematically searching for GRB–FRB spatial associations from 110 FRBs and 1440 GRBs. We find that one FRB event discovered by the Parkes telescope, FRB 171209, is spatially coincident with a historical long-duration GRB 110715A at z = 0.82. The afterglow of GRB 110715A is consistent with being powered by a millisecond magnetar. The extragalactic dispersion measure of FRB 171209 is in excess of that contributed by the intergalactic medium, which can be interpreted as being contributed by a young supernova remnant associated with the GRB. Overall, the significance of the association is (2.28–2.55)σ. If the association is indeed physical, our result suggests that the magnetars associated with long GRBs can be the progenitors of at least some FRBs.