ABSTRACT We analyze 24 binary radio pulsars in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) nine-year data set. We make 14 significant measurements of the Shapiro ...delay, including new detections in four pulsar-binary systems (PSRs J0613−0200, J2017+0603, J2302+4442, and J2317+1439), and derive estimates of the binary-component masses and orbital inclination for these MSP-binary systems. We find a wide range of binary pulsar masses, with values as low as for PSR J1918−0642 and as high as for PSR J1614−2230 (both 68.3% credibility). We make an improved measurement of the Shapiro timing delay in the PSR J1918−0642 and J2043+1711 systems, measuring the pulsar mass in the latter system to be (68.3% credibility) for the first time. We measure secular variations of one or more orbital elements in many systems, and use these measurements to further constrain our estimates of the pulsar and companion masses whenever possible. In particular, we used the observed Shapiro delay and periastron advance due to relativistic gravity in the PSR J1903+0327 system to derive a pulsar mass of (68.3% credibility). We discuss the implications that our mass measurements have on the overall neutron-star mass distribution, and on the "mass/orbital-period" correlation due to extended mass transfer.
We present a Chandra Director's Discretionary Time observation of PSR J1119-6127 and its compact X-ray pulsar wind nebula (PWN) obtained on 2016 October 27, three months after the Fermi and Swift ...detection of millisecond bursts in hard X-rays, accompanied by a 160 times increase in flux. This magnetar-like activity, the first observed from a rotation-powered radio pulsar, provides an important probe of the physical processes that differentiate radio pulsars from magnetars. The post-burst X-ray spectrum of the pulsar can be described by a single power-law model with a photon index of 2.0 0.2 and an unabsorbed flux of 10−12 erg cm−2 s−1 in the 0.5-7.0 keV energy range. At the time of Chandra observations, the pulsar was still brighter by a factor of ∼22 in comparison with its quiescence. The X-ray images reveal a nebula brighter than in the pre-burst Chandra observations (from 2002 and 2004), with an unabsorbed flux of 10−13 erg cm−2 s−1. This implies a current X-ray efficiency of at a distance of 8.4 kpc. In addition, a faint torus-like structure is visible along the southeast-northwest direction and a jet-like feature perpendicular to the torus toward the southwest. The PWN is best fitted by an absorbed power-law with a photon index of 2.2 0.5 (post-burst). While the pulsar can still be energetically powered by rotation, the observed changes in PSR J1119-6127 and its PWN following the magnetar-like bursts point to an additional source of energy powered by its high magnetic field.
Many physically motivated extensions to general relativity (GR) predict substantial deviations in the properties of spacetime surrounding massive neutron stars. We report the measurement of a 2.01 ± ...0.04 solar mass (M⊙) pulsar in a 2.46-hour orbit with a 0.172 ± 0.003 M⊙ white dwarf. The high pulsar mass and the compact orbit make this system a sensitive laboratory of a previously untested strong-field gravity regime. Thus far, the observed orbital decay agrees with GR, supporting its validity even for the extreme conditions present in the system. The resulting constraints on deviations support the use of GR-based templates for ground-based gravitational wave detectors. Additionally, the system strengthens recent constraints on the properties of dense matter and provides insight to binary stellar astrophysics and pulsar recycling.
Abstract
Context.
By providing information about the location of scattering material along the line of sight (LoS) to pulsars, scintillation arcs are a powerful tool for exploring the distribution of ...ionized material in the interstellar medium (ISM). Here, we present observations that probe the ionized ISM on scales of ∼0.001–30 au.
Aims.
We have surveyed pulsars for scintillation arcs in a relatively unbiased sample with DM < 100 pc cm
−3
. We present multifrequency observations of 22 low to moderate DM pulsars. Many of the 54 observations were also observed at another frequency within a few days.
Methods.
For all observations, we present dynamic spectra, autocorrelation functions, and secondary spectra. We analyze these data products to obtain scintillation bandwidths, pulse broadening times, and arc curvatures.
Results.
We detect definite or probable scintillation arcs in 19 of the 22 pulsars and 34 of the 54 observations, showing that scintillation arcs are a prevalent phenomenon. The arcs are better defined in low DM pulsars. We show that well-defined arcs do not directly imply anisotropy of scattering. Only the presence of reverse arclets and a deep valley along the delay axis, which occurs in about 20% of the pulsars in the sample, indicates substantial anisotropy of scattering.
Conclusions.
The survey demonstrates substantial patchiness of the ionized ISM on both astronomical-unit-size scales transverse to the LoS and on ∼100 pc scales along it. We see little evidence for distributed scattering along most lines of sight in the survey.
The Double Pulsar (PSR J0737−3039) is the only neutron star–neutron star (NS–NS) binary in which both NSs have been detectable as radio pulsars. The Double Pulsar has been assumed to dominate the ...Galactic NS–NS binary merger rate
${\cal R}_{\rm g}$
among all known systems, solely based on the properties of the first-born, recycled pulsar (PSR J0737−3039A, or A) with an assumption for the beaming correction factor of 6. In this work, we carefully correct observational biases for the second-born, non-recycled pulsar (PSR J0737−0737B, or B) and estimate the contribution from the Double Pulsar on
${\cal R}_{\rm g}$
using constraints available from both A and B. Observational constraints from the B pulsar favour a small beaming correction factor for A (∼2), which is consistent with a bipolar model. Considering known NS–NS binaries with the best observational constraints, including both A and B, we obtain
${\cal R}_{\rm g}=21_{-14}^{+28}$
Myr−1 at 95 per cent confidence from our reference model. We expect the detection rate of gravitational waves from NS–NS inspirals for the advanced ground-based gravitational-wave detectors is to be
$8^{+10}_{-5}$
yr−1 at 95 per cent confidence. Within several years, gravitational-wave detections relevant to NS–NS inspirals will provide us useful information to improve pulsar population models.
Abstract
We use the upgraded Giant Metrewave Radio Telescope (uGMRT) to measure scintillation arc properties in six bright canonical pulsars with simultaneous dual-frequency coverage. These ...observations, at frequencies from 300 to 750 MHz, allowed for detailed analysis of arc evolution across frequency and epoch. We perform more robust determinations of frequency dependence for arc curvature, scintillation bandwidth, and scintillation timescale, and comparison between arc curvature and pseudo-curvature than allowed by single-frequency-band-per-epoch measurements, which we find to agree with theory and previous literature. We find a strong correlation between arc asymmetry and arc curvature, which we have replicated using simulations, and attribute to a bias in the Hough transform approach to scintillation arc analysis. Possible evidence for an approximately week-long timescale over which a given scattering screen dominates signal propagation was found by tracking visible scintillation arcs in each epoch in PSR J1136+1551. The inclusion of a 155-minute observation allowed us to resolve the scale of scintillation variations on short timescales, which we find to be directly tied to the amount of interstellar medium sampled over the observation. Some of our pulsars showed either consistent or emerging asymmetries in arc curvature, indicating instances of refraction across their lines of sight. Significant features in various pulsars, such as multiple scintillation arcs in PSR J1136+1551 and flat arclets in PSR J1509+5531, that have been found in previous works, were also detected. The simultaneous multiple-band observing capability of the upgraded GMRT shows excellent promise for future pulsar scintillation work.
Abstract
Although neutron star–black hole binaries have been identified through mergers detected in gravitational waves, a pulsar–black hole binary has yet to be detected. While short-period binaries ...are detectable due to a clear signal in the pulsar’s timing residuals, effects from a long-period binary could be masked by other timing effects, allowing them to go undetected. In particular, a long-period binary measured over a small subset of its orbital period could manifest via time derivatives of the spin frequency incompatible with isolated pulsar properties. We assess the possibility of pulsars having unknown companions in long-period binaries and put constraints on the range of binary properties that may remain undetected in current data, but that may be detectable with further observations. We find that for 35% of canonical pulsars with published higher-order derivatives, the precision of measurements is not enough to confidently reject binarity (period ≳2 kyr), and that a black hole binary companion could not be ruled out for a sample of pulsars without published constraints if the period is >1 kyr. While we find no convincing cases in the literature, we put more stringent limits on orbital period and longitude of periastron for the few pulsars with published higher-order frequency derivatives (
n
≥ 3). We discuss the detectability of candidates and find that a sample pulsar in a 100 yr orbit could be detectable within 5–10 yr.
Abstract
We report on the 2020 reactivation of the energetic high magnetic field pulsar PSR J1846–0258 and its pulsar wind nebula (PWN) after 14 yr of quiescence with new Chandra and Green Bank ...Telescope observations. The emission of short-duration bursts from J1846–0258 was accompanied by an enhancement of X-ray persistent flux and significant spectral softening, similar to those observed during its first bursting episode in 2006. The 2020 pulsar spectrum is described by a power-law model with a photon index Γ = 1.7 ± 0.3 in comparison to a Γ = 1.2 ± 0.1 before outburst, and shows evidence of an emerging thermal component with blackbody temperature
kT
= 0.7 ± 0.1 keV. The 0.5–10 keV unabsorbed flux increased from
× 10
−12
erg cm
−2
s
−1
in quiescence to
× 10
−11
erg cm
−2
s
−1
following the outburst. We did not detect any radio pulsations from the pulsar at 2 GHz, and we place an upper limit of 7.1
μ
Jy and 55 mJy for the coherent pulsed emission and single pulses, respectively. The 2020 PWN spectrum, characterized by a photon index of 1.92 ± 0.04 and X-ray luminosity of (1.2 ± 0.1) × 10
35
erg s
−1
at a distance of 5.8 kpc, is consistent with those observed before the outburst. An analysis of regions closer to the pulsar shows small-scale time variabilities and brightness changes over the 20 yr period from 2000 to 2020, while the photon indices did not change. We conclude that the outburst in PSR J1846–0258 is a combination of crustal and magnetospheric effects, with no significant burst-induced variability in its PWN based on the current observations.
ABSTRACT We report on an effort to extract and monitor interstellar scintillation parameters in regular timing observations collected for the North American Nanohertz Observatory for Gravitational ...Waves pulsar timing array. Scattering delays are measured by creating dynamic spectra for each pulsar and observing epoch of wide-band observations centered near 1500 MHz and carried out at the Green Bank Telescope and the Arecibo Observatory. The ∼800 MHz wide frequency bands imply dramatic changes in scintillation bandwidth across the bandpass, and a stretching routine has been included to account for this scaling. For most of the 10 pulsars for which the scaling has been measured, the bandwidths scale with frequency less steeply than expected for a Kolmogorov medium. We find estimated scattering delay values that vary with time by up to an order of magnitude. The mean measured scattering delays are similar to previously published values and are slightly higher than predicted by interstellar medium models. We investigate the possibility of increasing the timing precision by mitigating timing errors introduced by the scattering delays. For most of the pulsars, the uncertainty in the time of arrival of a single timing point is much larger than the maximum variation of the scattering delay, suggesting that diffractive scintillation remains as only a negligible part of their noise budget.
PDF
