48 research outputs found
The Search For Pulsar Wind Nebulae in the Very High Energy Gamma-ray Regime
No full textThe aim of this Thesis is to study the development of pulsar wind nebulae in the TeV regime and in doing so uncover more sources which have as yet not been observed at these wavelengths. It is found that the extent of pulsar wind nebula in the TeV gamma-ray increases with its age while no developmental relationship is seen concerning
the luminosity or spectral index of the nebulae when observed in the TeV gamma-ray regime due to uncertainties in the measurements available.
TeV gamma-ray upper limits are calculated for several nebulae observed in the X-ray regime allowing the strength of their magnetic fields to be constrained but only one new source, which was previously confused with its companion, was discovered, the Eel Nebula.
Predictions of the fluxes of many of the sources for which upper limits are derived in this work have been calculated from observations of their emission in X-rays and some of these sources should be uncovered with the next generation CTA instrument
Comparing recent PTA results on the nanohertz stochastic gravitational wave background - full noise and GWB parameter comparison plots
No full text<p>A full collection of plots comparing the noise properties of individual pulsars and gravitational wave background parameters discussed in the companion paper <em>Comparing recent PTA results on the nanohertz stochastic gravitational wave background</em> (IPTA 2024).</p>
<p><code>Section4_GWB_comparison.zip</code> supplements and expands section 4.1, "Comparing the published GWB measurements," of IPTA (2024). It contains parameter difference distributions for GWB model parameters. There are four different models included. The HD correlated powerlaw (PL) model make up the basis for Figure 2. Additionally, there are three comparisons not included in IPTA (2024). First, comparisons the common uncorrelated red noise (CURN) PL model are included. Finally, comparisons of two free spectral (FS) models (HD and CURN) are included. These comparisons fit the HD and CURN FS posteriors using the <code>ceffyl</code> software package, and then compare the parameters of the resulting powerlaw fits.</p>
<p><code>Section5_Noise_comparison.zip</code> supplements section 5, "Comparing Pulsar Noice Properties," of IPTA (2024). It contains plots for 27 pulsars timed by more than one PTA collaboration, including the plots for PSR J1012+5307, which are presented in Figure 7. The plots include noise parameter posteriors, time domain GP realizations, TOA residuals, and TOA radio frequency.</p>
European Pulsar Timing Array
No full textThe European Pulsar Timing Array is a collaboration that has recently been formed between the five major radio observatories in Europe: Jodrell Bank, Effelsberg, Westerbork, Nançay and Sardinia. Together we work towards detecting gravitational waves. We combine the individual strengths of all the different observatories to obtain improved results. We give a short introduction on the partners, goals and instrumentation of this collaboration. Besides gravitational wave detection, the EPTA collaboration is sharing data to optimize timing on, for example, millisecond binary pulsars. We present some recent results of combining datasets of the four telescopes now in use for the EPTA
The European Pulsar Timing Array: current efforts and a LEAP toward the future
No full textInternational audienceThe European Pulsar Timing Array (EPTA) is a multi-institutional, multi-telescope collaboration, with the goal of using high-precision pulsar timing to directly detect gravitational waves. In this article we discuss the EPTA member telescopes, current achieved timing precision, and near-future goals. We also report a preliminary upper limit to the amplitude of a gravitational wave background. We also discuss the Large European Array for Pulsars, in which the five major European telescopes involved in pulsar timing will be combined to provide a coherent array that will give similar sensitivity to the Arecibo radio telescope, and larger sky coverage
IPTA DR2 - GWB analysis MCMC output
No full textIPTA DR2 common red noise, MCMC output
These files are the primary output from a Markov chain Monte Carlo (MCMC) sampling process. They are samples from the posterior probability distribution for a particular model described in the companion paper.
Each zipped tarball contains four files. The "chain" file has several tab-separated columns, each of which corresponds to a model parameter, except the last four which are metadata. The parameter names (including metadata) are listed in the companion "params" file. The frequencies used in the common red noise models are listed in the "crn_frequencies" file. Additional information is provided in a README file.
Each row of the chain file is one sample from the model posterior. The first samples at the beginning of the MCMC are the "burn-in" phase, before the chain has converged to the posterior. We recommend discarding the first ~25% of samples before using them to make inferences
The International Pulsar Timing Array second data release : search for an isotropic gravitational wave background
No full textWe searched for an isotropic stochastic gravitational wave background in the second data release of the International Pulsar Timing Array, a global collaboration synthesizing decadal-length pulsar-timing campaigns in North America, Europe, and Australia. In our reference search for a power-law strain spectrum of the form hc = A(f/1, yr-α, we found strong evidence for a spectrally similar low-frequency stochastic process of amplitude A = 3.8+6.3-2.5 × 10-15 and spectral index α =-0.5 ± 0.5, where the uncertainties represent 95 per cent credible regions, using information from the auto- A nd cross-correlation terms between the pulsars in the array. For a spectral index of α =-2/3, as expected from a population of inspiralling supermassive black hole binaries, the recovered amplitude is A = 2.8+1.2-0.8 × 10-15. None the less, no significant evidence of the Hellings-Downs correlations that would indicate a gravitational-wave origin was found. We also analysed the constituent data from the individual pulsar timing arrays in a consistent way, and clearly demonstrate that the combined international data set is more sensitive. Furthermore, we demonstrate that this combined data set produces comparable constraints to recent single-array data sets which have more data than the constituent parts of the combination. Future international data releases will deliver increased sensitivity to gravitational wave radiation, and significantly increase the detection probability
The International Pulsar Timing Array second data release: Search for an isotropic gravitational wave background
No full textWe searched for an isotropic stochastic gravitational wave background in the second data release of the International Pulsar Timing Array, a global collaboration synthesizing decadal-length pulsar-timing campaigns in North America, Europe, and Australia. In our reference search for a power law strain spectrum of the form hc = A(ƒ/1yr−1)α, we found strong evidence for a spectrally-similar low-frequency stochastic process of amplitude A = 3.8+6.3-2.5×10−15 and spectral index α = −0.5±0.5, where the uncertainties represent 95% credible regions, using information from the auto- and cross-correlation terms between the pulsars in the array. For a spectral index of α = −2/3, as expected from a population of inspiralling supermassive black hole binaries, the recovered amplitude is A = 2.8 +1.2−0.8 × 10−15. Nonetheless, no significant evidence of the Hellings-Downs correlations that would indicate a gravitational-wave origin was found. We also analyzed the constituent data from the individual pulsar timing arrays in a consistent way, and clearly demonstrate that the combined international data set is more sensitive. Furthermore, we demonstrate that this combined data set produces comparable constraints to recent single-array data sets which have more data than the constituent parts of the combination. Future international data releases will deliver increased sensitivity to gravitational wave radiation, and significantly increase the detection probability.<br/
The Indian Pulsar Timing Array: First data release
No full textWe present the pulse arrival times and high-precision dispersion measure estimates for 14 millisecond pulsars observed simultaneously in the 300-500 MHz and 1260-1460 MHz frequency bands using the upgraded Giant Metrewave Radio Telescope. The data spans over a baseline of 3.5 years (2018-2021), and is the first official data release made available by the Indian Pulsar Timing Array collaboration. This data release presents a unique opportunity for investigating the interstellar medium effects at low radio frequencies and their impact on the timing precision of pulsar timing array experiments. In addition to the dispersion measure time series and pulse arrival times obtained using both narrowband and wideband timing techniques, we also present the dispersion measure structure function analysis for selected pulsars. Our ongoing investigations regarding the frequency dependence of dispersion measures have been discussed. Based on the preliminary analysis for five millisecond pulsars, we do not find any conclusive evidence of chromaticity in dispersion measures. Data from regular simultaneous two-frequency observations are presented for the first time in this work. This distinctive feature leads us to the highest precision dispersion measure estimates obtained so far for a subset of our sample. Simultaneous multi-band upgraded Giant Metrewave Radio Telescope observations in 300-500 MHz and 1260-1460 MHz are crucial for high-precision dispersion measure estimation and for the prospect of expanding the overall frequency coverage upon the combination of data from the various Pulsar Timing Array consortia in the near future. Parts of the data presented in this work are expected to be incorporated into the upcoming third data release of the International Pulsar Timing Array
Astrophysics Milestones for Pulsar Timing Array Gravitational-wave Detection
No full textInternational audienceThe NANOGrav Collaboration reported strong Bayesian evidence for a common-spectrum stochastic process in its 12.5 yr pulsar timing array data set, with median characteristic strain amplitude at periods of a year of . However, evidence for the quadrupolar Hellings & Downs interpulsar correlations, which are characteristic of gravitational-wave signals, was not yet significant. We emulate and extend the NANOGrav data set, injecting a wide range of stochastic gravitational-wave background (GWB) signals that encompass a variety of amplitudes and spectral shapes, and quantify three key milestones. (I) Given the amplitude measured in the 12.5 yr analysis and assuming this signal is a GWB, we expect to accumulate robust evidence of an interpulsar-correlated GWB signal with 15–17 yr of data, i.e., an additional 2–5 yr from the 12.5 yr data set. (II) At the initial detection, we expect a fractional uncertainty of 40% on the power-law strain spectrum slope, which is sufficient to distinguish a GWB of supermassive black hole binary origin from some models predicting more exotic origins. (III) Similarly, the measured GWB amplitude will have an uncertainty of 44% upon initial detection, allowing us to arbitrate between some population models of supermassive black hole binaries. In addition, power-law models are distinguishable from those having low-frequency spectral turnovers once 20 yr of data are reached. Even though our study is based on the NANOGrav data, we also derive relations that allow for a generalization to other pulsar timing array data sets. Most notably, by combining the data of individual arrays into the International Pulsar Timing Array, all of these milestones can be reached significantly earlier
Comparing Recent Pulsar Timing Array Results on the Nanohertz Stochastic Gravitational-wave Background
No full textThe Australian, Chinese, European, Indian, and North American pulsar timing array (PTA) collaborations recently reported, at varying levels, evidence for the presence of a nanohertz gravitational-wave background (GWB). Given that each PTA made different choices in modeling their data, we perform a comparison of the GWB and individual pulsar noise parameters across the results reported from the PTAs that constitute the International Pulsar Timing Array (IPTA). We show that despite making different modeling choices, there is no significant difference in the GWB parameters that are measured by the different PTAs, agreeing within 1σ. The pulsar noise parameters are also consistent between different PTAs for the majority of the pulsars included in these analyses. We bridge the differences in modeling choices by adopting a standardized noise model for all pulsars and PTAs, finding that under this model there is a reduction in the tension in the pulsar noise parameters. As part of this reanalysis, we “extended” each PTA’s data set by adding extra pulsars that were not timed by that PTA. Under these extensions, we find better constraints on the GWB amplitude and a higher signal-to-noise ratio for the Hellings-Downs correlations. These extensions serve as a prelude to the benefits offered by a full combination of data across all pulsars in the IPTA, i.e., the IPTA’s Data Release 3, which will involve not just adding in additional pulsars but also including data from all three PTAs where any given pulsar is timed by more than a single PTA
