The Pulsar Machine II (PuMa-II) is the new flexible pulsar processing back-end system at the Westerbork Synthesis Radio Telescope (WSRT), specifically designed to take advantage of the upgraded WSRT. ...The instrument is based on a computer cluster running the Linux operating system, with minimal custom hardware. A maximum of 160 MHz analog bandwidth sampled as8 × 20 MHz
8
×
20
MHz
subbands with 8-bit resolution can be recorded on disks attached to separate computer nodes. Processing of the data is done in the additional 32 nodes allowing near real time coherent dedispersion for most pulsars observed at the WSRT. This has doubled the bandwidth for pulsar observations in general, and has enabled the use of coherent dedispersion over a bandwidth 8 times larger than was previously possible at the WSRT. PuMa-II is one of the widest bandwidth coherent dedispersion machines currently in use and has a maximum time resolution of 50 ns. The system is now routinely used for high-precision pulsar timing studies, polarization studies, single pulse work, and a variety of other observational work.
Pulsars in the Galactic centre promise to enable unparalleled tests of gravity theories and black hole physics and to serve as probes of the stellar formation history and evolution and the ...interstellar medium in the complex central region of the Milky Way. The community has surveyed the innermost region of the galaxy for decades without detecting a population of pulsars, which is puzzling. A strong scattering of the pulsed signals in this particular direction has been argued to be a potential reason for the non-detections. Scattering has a strong inverse dependence on observing frequency, therefore an effective way to alleviate its effect is to use higher frequencies in a survey for pulsars in the Galactic centre, in particular, close to the supermassive black hole Sagittarius A*. We present the first pulsar survey at short millimetre wavelengths, using several frequency bands between 84 and 156 GHz (λ = 3.5–1.92 mm), targeted to the Galactic centre. The observations were made with the Institut de Radioastronomie Millimétrique 30m Telescope in 28 epochs between 2016 December and 2018 May. This survey is the first that is essentially unaffected by scattering and therefore unbiased in population coverage, including fast-spinning pulsars that might be out of reach of lower-frequency Galactic centre surveys. We discovered no new pulsars and relate this result mainly to the decreased flux density of pulsars at high frequencies, combined with our current sensitivity. However, we demonstrate that surveys at these extremely high radio frequencies are capable of discovering new pulsars, analyse their sensitivity limits with respect to a simulated Galactic centre pulsar population, and discuss the main challenges and possible improvements for similar surveys in the future.
Revisiting profile instability of PSR J1022+1001 Padmanabh, Prajwal V; Barr, Ewan D; Champion, David J ...
Monthly notices of the Royal Astronomical Society,
01/2021, Letnik:
500, Številka:
1
Journal Article
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ABSTRACT
Millisecond pulsars in timing arrays can act as probes for gravitational wave detection and improving the Solar system ephemerides among several other applications. However, the stability of ...the integrated pulse profiles can limit the precision of the ephemeris parameters and in turn the applications derived from it. It is thus crucial for the pulsars in the array to have stable integrated pulse profiles. Here we present evidence for long-term profile instability in PSR J1022+1001 which is currently included in the European and Parkes pulsar timing arrays. We apply a new evaluation method to an expanded data set ranging from the Effelsberg Pulsar Observing System backend used in the 1990s to that of data from the current PSRIX backend at the Effelsberg Radio Telescope. We show that this intrinsic variability in the pulse shape persists over time-scales of years. We investigate if systematic instrumental effects like polarization calibration or signal propagation effects in the interstellar medium causes the observed profile instability. We find that the total variation cannot be fully accounted for by instrumental and propagation effects. This suggests additional intrinsic effects as the origin for the variation. We finally discuss several factors that could lead to the observed behaviour and comment on the consequent implications.
We present new limits on an isotropic stochastic gravitational-wave background (GWB) using a six pulsar data set spanning 18 yr of observations from the 2015 European Pulsar Timing Array data ...release. Performing a Bayesian analysis, we fit simultaneously for the intrinsic noise parameters for each pulsar, along with common correlated signals including clock, and Solar system ephemeris errors, obtaining a robust 95 per cent upper limit on the dimensionless strain amplitude A of the background of A < 3.0 × 10−15 at a reference frequency of 1 yr−1 and a spectral index of 13/3, corresponding to a background from inspiralling supermassive black hole binaries, constraining the GW energy density to Ωgw(f)h
2 < 1.1 × 10−9 at 2.8 nHz. We also present limits on the correlated power spectrum at a series of discrete frequencies, and show that our sensitivity to a fiducial isotropic GWB is highest at a frequency of ∼5 × 10−9 Hz. Finally, we discuss the implications of our analysis for the astrophysics of supermassive black hole binaries, and present 95 per cent upper limits on the string tension, Gμ/c
2, characterizing a background produced by a cosmic string network for a set of possible scenarios, and for a stochastic relic GWB. For a Nambu–Goto field theory cosmic string network, we set a limit Gμ/c
2 < 1.3 × 10−7, identical to that set by the Planck Collaboration, when combining Planck and high-ℓ cosmic microwave background data from other experiments. For a stochastic relic background, we set a limit of
$\Omega ^\mathrm{relic}_\mathrm{gw}(f)h^2<1.2 \times 10^{-9}$
, a factor of 9 improvement over the most stringent limits previously set by a pulsar timing array.
Simultaneous observations at four different frequencies, 313, 607, 1380, and 4850 MHz, for three pulsars, PSRs B0031-07, B0809+74, and B2319+60, are reported in this paper. Identified null and burst ...pulses are highly concurrent across more than a decade of frequency. A small fraction of non-concurrent pulses (< or =, slant3%) is observed, most of which occur at the transition instances. We report, with very high significance for the first time, the full broadband nature of the nulling phenomenon in these three pulsars. These results suggest that nulling invokes changes on the global magnetospheric scale.
ABSTRACT
We report on multifrequency radio observations of the new magnetar Swift J1818.0−1607, following it for more than one month with high cadence. The observations commenced less than 35 h after ...its registered first outburst. We obtained timing, polarization, and spectral information. Swift J1818.0−1607 has an unusually steep spectrum for a radio emitting magnetar and also has a relatively narrow and simple pulse profile. The position angle swing of the polarization is flat over the pulse profile, possibly suggesting that our line of sight grazes the edge of the emission beam. This may also explain the steep spectrum. The spin evolution shows large variation in the spin-down rate, associated with four distinct timing events over the course of our observations. Those events may be related to the appearance and disappearance of a second pulse component. The first timing event coincides with our actual observations, while we did not detect significant changes in the emission properties that could reveal further magnetospheric changes. Characteristic ages inferred from the timing measurements over the course of months vary by nearly an order of magnitude. A longer-term spin-down measurement over approximately 100 d suggests a characteristic age of about 500 yr, larger than previously reported. Though Swift J1818.0−1607 could still be one of the youngest neutron stars (and magnetars) detected so far, we caution using the characteristic age as a true-age indicator given the caveats behind its calculation.
We have searched for continuous gravitational wave (CGW) signals produced by individually resolvable, circular supermassive black hole binaries (SMBHBs) in the latest European Pulsar Timing Array ...(EPTA) data set, which consists of ultraprecise timing data on 41-ms pulsars. We develop frequentist and Bayesian detection algorithms to search both for monochromatic and frequency-evolving systems. None of the adopted algorithms show evidence for the presence of such a CGW signal, indicating that the data are best described by pulsar and radiometer noise only. Depending on the adopted detection algorithm, the 95 per cent upper limit on the sky-averaged strain amplitude lies in the range ... This limit varies by a factor of five, depending on the assumed source position and the most constraining limit is achieved towards the positions of the most sensitive pulsars in the timing array. The most robust upper limit - obtained via a full Bayesian analysis searching simultaneously over the signal and pulsar noise on the subset of ours six best pulsars -- is ... These limits, the most stringent to date at f < 10...nHz, exclude the presence of sub-centiparsec binaries with chirp mass ... out to a distance of about 25 Mpc, and with ... out to a distance of about 1Gpc (...). We show that state-of-the-art SMBHB population models predict <1 per cent probability of detecting a CGW with the current EPTA data set, consistent with the reported non-detection. We stress, however, that PTA limits on individual CGW have improved by almost an order of magnitude in the last five years. The continuing advances in pulsar timing data acquisition and analysis techniques will allow for strong astrophysical constraints on the population of nearby SMBHBs in the coming years. (ProQuest: ... denotes formulae/symbols omitted.)
Context.
Interstellar scintillation analysis of pulsars allows us to probe the small-scale distribution and inhomogeneities of the ionized interstellar medium. From the frequency scale of ...scintillation, one can estimate the geometric time delays from multipath propagation, a source of (typically) unmodeled, correlated noise in pulsar timing. Interstellar scintillation analysis of well-timed pulsars is useful to quantify the effects of time delays and may lead to improved timing precision, enhancing the probability of detecting gravitational waves.
Aims.
Our priority is to present the data set and the basic measurements of scintillation parameters of pulsars, employing long-term scintillation observations carried out from 2011 January to 2020 August by the European Pulsar Timing Array radio telescopes in the 21-cm and 11-cm bands. Additionally, we aim to identify future possible lines of study using this long-term scintillation data set.
Methods.
The autocorrelation function of dynamic spectra has been used to estimate the scintillation bandwidth
v
d
and scintillation timescale
τ
d
.
Results.
We present the long-term time series of
v
d
and
τ
d
for 13 pulsars. Sanity checks and comparisons indicate that the scintillation parameters of our work and previously published works are mostly consistent. For two pulsars, PSRs J1857+0943 and J1939+2134, we were able to obtain measurements of the
v
d
at both bands, which allowed us to derive the time series of frequency scaling indices with a mean and a standard deviation of 2.82 ± 1.95 and 3.18 ± 0.60, respectively. We found some interesting features which will be studied in more detail in subsequent papers in this series: (i) in the time series of PSR J1939+2134, where
v
d
and
τ
d
sharply decrease associated with a sharp increase in the dispersion measure; (ii) PSR J0613-0200 and PSR J0636+5126 show a strong annual variation in the time series of the
τ
d
; and (iii) PSR J1939+2134 shows a weak anticorrelation between the scintillation timescale and the dispersion in Westerbork Synthesis Radio Telescope data.
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