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We investigate the use of bright single pulses from the Crab pulsar to determine separately the dispersion measure (DM) for the Main Pulse and Interpulse components. We develop two approaches using cross-correlation functions (CCFs). The first method computes the CCF of the total intensity of each of the 64 frequency channels with a reference channel and converts the time lag of maximum correlation into a DM. The second method separately computes the CCF between every pair of channels for each individual bright pulse and extracts an average DM from the distribution of all channel-pair DMs. Both methods allow the determination of the DM with a relative uncertainty of better than 10⁻⁵and provide robust estimates for the uncertainty of the best-fit value. We find differences in DM between the Main Pulse, the Low Frequency Interpulse, and the High Frequency Interpulse using both methods in a frequency range from 4 to 6 GHz. Earlier observations of the High Frequency Interpulse carried out by Hankins et al. (2016) resulted in DM_HFIP–DM_MPof 0.010 ± 0.016 pc cm⁻³. Our results indicate a DM_HFIP–DM_MPof 0.0127 ± 0.0011 pc cm⁻³(with DM_compbeing the DM value of the respective emission component), confirming earlier results with an independent method. During our studies we also find a relation between the brightness of single pulses in the High Frequency Interpulse and their DM. We also discuss the application of the developed methods on the identification of substructures in the case of Fast Radio Bursts.

 

Abstract With the Expanded Long Wavelength Array (ELWA) and pulsar binning techniques, we searched for off-pulse emission from PSR B0950+08 at 76 MHz. Previous studies suggest that off-pulse emission can be due to pulsar wind nebulae (PWNe) in younger pulsars. Other studies, such as that done by Basu et al. (2012), propose that in older pulsars this emission extends to some radius that is on the order of the light cylinder radius, and is magnetospheric in origin. Through imaging analysis we conclude that this older pulsar with a spin-down age of 17 Myr has a surrounding PWN, which is unexpected since as a pulsar ages its PWN spectrum is thought to shift from being synchrotron to inverse-Compton-scattering dominated. At 76 MHz, the average flux density of the off-pulse emission is 0.59 ± 0.16 Jy. The off-pulse emission from B0950+08 is ∼ 110 ± 17 arcseconds (0.14 ± 0.02 pc) in size, extending well-beyond the light cylinder diameter and ruling out a magnetospheric origin. Using data from our observation and the surveys VLSSr, TGSS, NVSS, FIRST, and VLASS, we have found that the spectral index for B0950+08 is about −1.36 ± 0.20, while the PWN’s spectral index is steeper than −1.85 ± 0.45. 

Abstract In this work, we present polarization profiles for 23 millisecond pulsars observed at 820 and 1500 MHz with the Green Bank Telescope as part of the NANOGrav pulsar timing array. We calibrate the data using Mueller matrix solutions calculated from observations of PSRs B1929+10 and J1022+1001. We discuss the polarization profiles, which can be used to constrain pulsar emission geometry, and present both the first published radio polarization profiles for nine pulsars and the discovery of very low-intensity average profile components (“microcomponents”) in four pulsars. We obtain the Faraday rotation measures for each pulsar and use them to calculate the Galactic magnetic field parallel to the line of sight for different lines of sight through the interstellar medium. We fit for linear and sinusoidal trends in time in the dispersion measure and Galactic magnetic field and detect magnetic field variations with a period of 1 yr in some pulsars, but overall find that the variations in these parameters are more consistent with a stochastic origin. 

Abstract The Green Bank North Celestial Cap survey is a 350 MHz all-sky survey for pulsars and fast radio transients using the Robert C. Byrd Green Bank Telescope. To date, the survey has discovered over 190 pulsars, including 33 millisecond pulsars and 24 rotating radio transients. Several exotic pulsars have been discovered in the survey, including PSR J1759+5036, a binary pulsar with a 176 ms spin period in an orbit with a period of 2.04 days, an eccentricity of 0.3, and a projected semi-major axis of 6.8 light seconds. Using seven years of timing data, we are able to measure one post–Keplerian parameter, advance of periastron, which has allowed us to constrain the total system mass to 2.62 ± 0.03 M ⊙ . This constraint, along with the spin period and orbital parameters, suggests that this is a double neutron star system, although we cannot entirely rule out a pulsar-white dwarf binary. This pulsar is only detectable in roughly 45% of observations, most likely due to scintillation. However, additional observations are required to determine whether there may be other contributing effects. 

The International Pulsar Timing Array 2nd data release is the combination of data sets from worldwide collaborations. In this study, we search for continuous waves: gravitational wave signals produced by individual supermassive black hole binaries in the local universe. We consider binaries on circular orbits and neglect the evolution of orbital frequency over the observational span. We find no evidence for such signals and set sky averaged 95 per cent upper limits on their amplitude h95. The most sensitive frequency is 10 nHz with h95 = 9.1 × 10−15. We achieved the best upper limit to date at low and high frequencies of the PTA band thanks to improved effective cadence of observations. In our analysis, we have taken into account the recently discovered common red noise process, which has an impact at low frequencies. We also find that the peculiar noise features present in some pulsars data must be taken into account to reduce the false alarm. We show that using custom noise models is essential in searching for continuous gravitational wave signals and setting the upper limit.

 

The 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.