Showing papers by "Timothy T. Pennucci published in 2016"
University of British Columbia1, Columbia University2, California Institute of Technology3, McGill University4, Lafayette College5, National Radio Astronomy Observatory6, Goddard Space Flight Center7, Cornell University8, Hillsdale College9, Université de Montréal10, Vancouver Coastal Health11, West Virginia University12, University of Manchester13, University of New Mexico14, University of Wisconsin–Milwaukee15, Max Planck Society16
TL;DR: In this article, a wide range of binary pulsar masses and orbital inclination were derived from the NANOGrav nine-year data set, with values as low as {m}{m{p}{p}}}={1.41}{1.09}^{+0.10}
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 ${m}_{{\rm{p}}}={1.18}_{-0.09}^{+0.10}\,{M}_{\odot }$ for PSR J1918−0642 and as high as ${m}_{{\rm{p}}}={1.928}_{-0.017}^{+0.017}\,{M}_{\odot }$ 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 ${m}_{{\rm{p}}}={1.41}_{-0.18}^{+0.21}\,{M}_{\odot }$ (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 ${m}_{{\rm{p}}}={1.65}_{-0.02}^{+0.02}\,{M}_{\odot }$ (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.
450 citations
Bielefeld University1, Max Planck Society2, Australia Telescope National Facility3, California Institute of Technology4, National Radio Astronomy Observatory5, Chinese Academy of Sciences6, Goddard Space Flight Center7, Albert Einstein Institution8, ASTRON9, Curtin University10, Cornell University11, INAF12, Pennsylvania State University13, Notre Dame of Maryland University14, University of Orléans15, Centre national de la recherche scientifique16, Peking University17, Hillsdale College18, University of British Columbia19, University of Edinburgh20, West Virginia University21, Vancouver Coastal Health22, University of Amsterdam23, Columbia University24, Monash University25, University of Manchester26, Lafayette College27, Texas Tech University28, University of Virginia29, Paris Diderot University30, Swinburne University of Technology31, University of Birmingham32, University of Wisconsin–Milwaukee33, Oberlin College34, University of New Mexico35, Huazhong University of Science and Technology36, University of Western Australia37, Southwest University38
TL;DR: In this article, the first joint analysis of the data from the three regional pulsar timing arrays (IPTA) is presented, i.e. of the first IPTA data set, and the approach presently followed for its combination and suggest improvements for future PTA research.
Abstract: The highly stable spin of neutron stars can be exploited for a variety of (astro)physical investigations. In particular, arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. Three such 'pulsar timing arrays' (PTAs) have been set up around the world over the past decades and collectively form the 'International' PTA (IPTA). In this paper, we describe the first joint analysis of the data from the three regional PTAs, i.e. of the first IPTA data set. We describe the available PTA data, the approach presently followed for its combination and suggest improvements for future PTA research. Particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. We identify and describe in detail several factors that complicate IPTA research and provide recommendations for future pulsar timing efforts. The first IPTA data release presented here (and available on-line) is used to demonstrate the IPTA's potential of improving upon gravitational-wave limits
412 citations
University of British Columbia1, Columbia University2, California Institute of Technology3, McGill University4, Lafayette College5, National Radio Astronomy Observatory6, Goddard Space Flight Center7, Hillsdale College8, Cornell University9, Université de Montréal10, Vancouver Coastal Health11, West Virginia University12, University of Manchester13, University of New Mexico14, University of Wisconsin–Milwaukee15, Max Planck Society16
TL;DR: In this article, a wide range of binary pulsar masses and orbital inclination were derived from the NANOGrav nine-year data set, with values as low as 1.41^{+0.21}-0.09}
Abstract: We analyze 24 binary radio pulsars in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) nine-year data set. We make fourteen significant measurements of 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 $m_{\rm p} = 1.18^{+0.10}_{-0.09}\text{M}_{\odot}$ for PSR J1918$-$0642 and as high as $m_{\rm p} = 1.928^{+0.017}_{-0.017}\text{M}_{\odot}$ 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 $m_{\rm p} = 1.41^{+0.21}_{-0.18}\text{M}_{\odot}$ (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 $m_{\rm p} = 1.65^{+0.02}_{-0.02}\text{M}_{\odot}$ (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.
329 citations
Goddard Space Flight Center1, Cornell University2, National Radio Astronomy Observatory3, Pennsylvania State University4, Franklin & Marshall College5, Montana State University6, University of British Columbia7, Hillsdale College8, California Institute of Technology9, McGill University10, West Virginia University11, Vancouver Coastal Health12, University of Texas at Brownsville13, Columbia University14, Max Planck Society15, Lafayette College16, University of Virginia17, University of Amsterdam18, University of Manchester19, University of Birmingham20, University of Wisconsin–Milwaukee21, Oberlin College22, University of New Mexico23, Huazhong University of Science and Technology24
TL;DR: In this paper, the authors compute upper limits on the nanohertz-frequency isotropic stochastic gravitational wave background (GWB) using the 9-year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration.
Abstract: We compute upper limits on the nanohertz-frequency isotropic stochastic gravitational wave background (GWB) using the 9 year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration. Well-tested Bayesian techniques are used to set upper limits on the dimensionless strain amplitude (at a frequency of 1 yr^(−1) for a GWB from supermassive black hole binaries of A_(gw) < 1.5 x 10^(-15). We also parameterize the GWB spectrum with a broken power-law model by placing priors on the strain amplitude derived from simulations of Sesana and McWilliams et al. Using Bayesian model selection we find that the data favor a broken power law to a pure power law with odds ratios of 2.2 and 22 to one for the Sesana and McWilliams prior models, respectively. Using the broken power-law analysis we construct posterior distributions on environmental factors that drive the binary to the GW-driven regime including the stellar mass density for stellar-scattering, mass accretion rate for circumbinary disk interaction, and orbital eccentricity for eccentric binaries, marking the first time that the shape of the GWB spectrum has been used to make astrophysical inferences. Returning to a power-law model, we place stringent limits on the energy density of relic GWs, Ω_(gw)(f)h^2 < 4.2 x 10^(-10). Our limit on the cosmic string GWB, Ω_(gw)(f)h^2 < 2.2 x 10^(-10), translates to a conservative limit on the cosmic string tension with Gµ < 3.3 x 10^(-8), a factor of four better than the joint Planck and high-l cosmic microwave background data from other experiments.
307 citations
Australia Telescope National Facility1, Curtin University2, University of California, San Diego3, Bielefeld University4, Max Planck Society5, California Institute of Technology6, Goddard Space Flight Center7, ASTRON8, Albert Einstein Institution9, INAF10, National Radio Astronomy Observatory11, Cornell University12, University of Orléans13, Centre national de la recherche scientifique14, Peking University15, Hillsdale College16, McGill University17, University of British Columbia18, University of Edinburgh19, Vancouver Coastal Health20, University of Amsterdam21, Columbia University22, University of Manchester23, Monash University24, West Virginia University25, Lafayette College26, University of Virginia27, Paris Diderot University28, Swinburne University of Technology29, University of Birmingham30, University of Wisconsin–Milwaukee31, Oberlin College32, University of New Mexico33, Chinese Academy of Sciences34, Huazhong University of Science and Technology35, Southwest University36, University of Western Australia37
TL;DR: In this paper, the authors analyse the stochastic properties of the 49 pulsars that comprise the first International Pulsar Timing Array (IPTA) data release and use Bayesian methodology, performing model selection to determine the optimal description of the signal present in each pulsar.
Abstract: We analyse the stochastic properties of the 49 pulsars that comprise the first International Pulsar Timing Array (IPTA) data release. We use Bayesian methodology, performing model selection to determine the optimal description of the stochastic signals present in each pulsar. In addition to spin-noise and dispersion-measure (DM) variations, these models can include timing noise unique to a single observing system, or frequency band. We show the improved radio-frequency coverage and presence of overlapping data from different observing systems in the IPTA data set enables us to separate both system and band-dependent effects with much greater efficacy than in the individual PTA data sets. For example, we show that PSR J1643−1224 has, in addition to DM variations, significant band-dependent noise that is coherent between PTAs which we interpret as coming from time-variable scattering or refraction in the ionised interstellar medium. Failing to model these different contributions appropriately can dramatically alter the astrophysical interpretation of the stochastic signals observed in the residuals. In some cases, the spectral exponent of the spin noise signal can vary from 1.6 to 4 depending upon the model, which has direct implications for the long-term sensitivity of the pulsar to a stochastic gravitational-wave (GW) background. By using a more appropriate model, however, we can greatly improve a pulsar's sensitivity to GWs. For example, including system and band-dependent signals in the PSR J0437−4715 data set improves the upper limit on a fiducial GW background by ∼ 60% compared to a model that includes DM variations and spin-noise only.
105 citations
TL;DR: In this paper, the authors analyze dispersion measure (DM) variations of 37 millisecond pulsars in the 9-year NANOGrav data release and constrain the sources of these variations.
Abstract: We analyze dispersion measure (DM) variations of 37 millisecond pulsars in the 9-year NANOGrav data release and constrain the sources of these variations. Variations are significant for nearly all pulsars, with characteristic timescales comparable to or even shorter than the average spacing between observations. Five pulsars have periodic annual variations, 14 pulsars have monotonically increasing or decreasing trends, and 13 pulsars show both effects. Several pulsars show correlations between DM excesses and lines of sight that pass close to the Sun. Mapping of the DM variations as a function of the pulsar trajectory can identify localized ISM features and, in one case, an upper limit to the size of the dispersing region of 13.2 AU. Finally, five pulsars show very nearly quadratic structure functions, which could be indicative of an underlying Kolmogorov medium. Four pulsars show roughly Kolmogorov structure functions and another four show structure functions less steep than Kolmogorov. One pulsar has too large an uncertainty to allow comparisons. We discuss explanations for apparent departures from a Kolmogorov-like spectrum, and show that the presence of other trends in the data is the most likely cause.
77 citations
University of Manchester1, West Virginia University2, Columbia University3, Cornell University4, Oberlin College5, Hillsdale College6, California Institute of Technology7, Goddard Space Flight Center8, University of British Columbia9, National Radio Astronomy Observatory10, Université de Montréal11, Vancouver Coastal Health12, Lafayette College13, University of Virginia14, University of New Mexico15, Max Planck Society16
TL;DR: In this paper, the authors extracted scintillation parameters for pulsars observed by the NANOGrav radio pulsar timing program and derived interstellar scattering-based transverse velocities assuming a scattering screen halfway between the pulsar and earth.
Abstract: We extract interstellar scintillation parameters for pulsars observed by the NANOGrav radio pulsar timing program. Dynamic spectra for the observing epochs of each pulsar were used to obtain estimates of scintillation timescales, scintillation bandwidths, and the corresponding scattering delays using a stretching algorithm to account for frequency-dependent scaling. We were able to measure scintillation bandwidths for 28 pulsars at 1500 MHz and 15 pulsars at 820 MHz. We examine scaling behavior for 17 pulsars and find indices ranging from $-0.7$ to $-3.6$. We were also able to measure scintillation timescales for six pulsars at 1500 MHz and seven pulsars at 820 MHz. There is fair agreement between our scattering delay measurements and electron-density model predictions for most pulsars, with some significant outliers likely resulting from frequency channel resolution limits outside of this range. We derive interstellar scattering-based transverse velocities assuming a scattering screen halfway between the pulsar and earth. We also calculate the location of the scattering screens assuming proper motion and interstellar scattering-derived transverse velocities are equal. We find no correlations between variations in scattering delay and either variations in dispersion measure or flux density. For most pulsars for which scattering delays were measurable, we find that time of arrival uncertainties for a given epoch are larger than our scattering delay measurements, indicating that variable scattering delays are currently subdominant in our overall noise budget but are important for achieving precisions of tens of ns or less.
68 citations
Cornell University1, West Virginia University2, Goddard Space Flight Center3, University of British Columbia4, National Radio Astronomy Observatory5, Hillsdale College6, California Institute of Technology7, University of East Anglia8, Université de Montréal9, Vancouver Coastal Health10, Columbia University11, University of Manchester12, Lafayette College13, Curtin University14, Australia Telescope National Facility15, University of Wisconsin–Milwaukee16, University of New Mexico17, Max Planck Society18
TL;DR: In this paper, the authors identify noise in timing residuals that exceeds that predicted for arrival time estimation for MSPs observed by the North American Nanohertz Observatory for Gravitational Waves.
Abstract: Gravitational wave (GW) astronomy using a pulsar timing array requires high-quality millisecond pulsars (MSPs), correctable interstellar propagation delays, and high-precision measurements of pulse times of arrival. Here we identify noise in timing residuals that exceeds that predicted for arrival time estimation for MSPs observed by the North American Nanohertz Observatory for Gravitational Waves. We characterize the excess noise using variance and structure function analyses. We find that 26 out of 37 pulsars show inconsistencies with a white-noise-only model based on the short timescale analysis of each pulsar, and we demonstrate that the excess noise has a red power spectrum for 15 pulsars. We also decompose the excess noise into chromatic (radio-frequency-dependent) and achromatic components. Associating the achromatic red-noise component with spin noise and including additional power-spectrum-based estimates from the literature, we estimate a scaling law in terms of spin parameters (frequency and frequency derivative) and data-span length and compare it to the scaling law of Shannon & Cordes. We briefly discuss our results in terms of detection of GWs at nanohertz frequencies.
66 citations
University of Virginia1, Lafayette College2, University of British Columbia3, Goddard Space Flight Center4, National Radio Astronomy Observatory5, Hillsdale College6, Cornell University7, California Institute of Technology8, Université de Montréal9, Vancouver Coastal Health10, Columbia University11, West Virginia University12, University of Manchester13, University of New Mexico14, Max Planck Society15
TL;DR: In this article, the authors measured the positions, proper motions, and parallaxes for 37 millisecond pulsars and compared these measurements to distances predicted by the NE2001 interstellar electron density model and found them to be in general agreement.
Abstract: Using the nine-year radio-pulsar timing data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), collected at Arecibo Observatory and the Green Bank Telescope, we have measured the positions, proper motions, and parallaxes for 37 millisecond pulsars. We report twelve significant parallax measurements and distance measurements, and eighteen lower limits on distance. We compare these measurements to distances predicted by the NE2001 interstellar electron density model and find them to be in general agreement. We use measured orbital-decay rates and spin-down rates to confirm two of the parallax distances and to place distance upper limits on other sources; these distance limits agree with the parallax distances with one exception, PSRJ1024–0719, which we discuss at length. Using the proper motions of the 37 NANOGrav pulsars in combination with other published measurements, we calculate the velocity dispersion of the millisecond pulsar population in Galactocentric coordinates. We find the radial, azimuthal, and perpendicular dispersions to be 46, 40, and 24 km s 1 - , respectively, in a model that allows for high-velocity outliers; or 81, 58, and 62 km s 1 - for the full population. These velocity dispersions are far smaller than those of the canonical pulsar population, and are similar to older Galactic disk populations. This suggests that millisecond pulsar velocities are largely attributable to their being an old population rather than being artifacts of their birth and evolution as neutron star binary systems. The components of these velocity dispersions follow similar proportions to other Galactic populations, suggesting that our results are not biased by selection effects.
64 citations
Cornell University1, Goddard Space Flight Center2, University of British Columbia3, National Radio Astronomy Observatory4, Hillsdale College5, California Institute of Technology6, McGill University7, Vancouver Coastal Health8, Columbia University9, West Virginia University10, University of Manchester11, Lafayette College12, University of Virginia13, University of Wisconsin–Milwaukee14, University of New Mexico15, Max Planck Society16
TL;DR: In this article, the authors assess contributions to the total variance from two additional effects: amplitude and phase jitter intrinsic to single pulses and changes in the interstellar impulse response from scattering.
Abstract: The use of pulsars as astrophysical clocks for gravitational wave (GW) experiments demands the highest possible timing precision. Pulse times of arrival (TOAs) are limited by stochastic processes that occur in the pulsar itself, along the line of sight through the interstellar medium, and in the measurement process. On timescales of seconds to hours, the TOA variance exceeds that from template-fitting errors due to additive noise. We assess contributions to the total variance from two additional effects: amplitude and phase jitter intrinsic to single pulses and changes in the interstellar impulse response from scattering. The three effects have different dependencies on time, frequency, and pulse signal-to-noise ratio. We use data on 37 pulsars from the North American Nanohertz Observatory for GWs to assess the individual contributions to the overall intraday noise budget for each pulsar. We detect jitter in 22 pulsars and estimate the average value of rms jitter in our pulsars to be $\sim 1\%$ of pulse phase. We examine how jitter evolves as a function of frequency and find evidence for evolution. Finally, we compare our measurements with previous noise parameter estimates and discuss methods to improve GW detection pipelines.
63 citations
University of Wisconsin–Milwaukee1, California Institute of Technology2, Lafayette College3, University of Erlangen-Nuremberg4, Goddard Space Flight Center5, Süleyman Demirel University6, West Virginia University7, University of British Columbia8, National Radio Astronomy Observatory9, Hillsdale College10, McGill University11, Columbia University12, Cornell University13, University of Virginia14, United States Naval Research Laboratory15, University of New Mexico16, Max Planck Society17
TL;DR: In this paper, the authors present updated radio timing observations along with new and archival optical data which show that PSR J1024-0719 is most likely in a long-period (2-20 kyr) binary system with a low-mass (≈0.4 M⊙), low-metallicity (z ≈ -0.9 dex) main-sequence star.
Abstract: PSR J1024–0719 is a millisecond pulsar that was long thought to be isolated. However, puzzling results concerning its velocity, distance, and low rotational period derivative have led to a reexamination of its properties. We present updated radio timing observations along with new and archival optical data which show that PSR J1024–0719 is most likely in a long-period (2–20 kyr) binary system with a low-mass (≈0.4 M⊙), low-metallicity (z ≈ -0.9 dex) main-sequence star. Such a system can explain most of the anomalous properties of this pulsar. We suggest that this system formed through a dynamical exchange in a globular cluster that ejected it into a halo orbit, which is consistent with the low observed metallicity for the stellar companion. Further astrometric and radio timing observations such as measurement of the third period derivative could strongly constrain the range of orbital parameters.
Cornell University1, West Virginia University2, Goddard Space Flight Center3, University of British Columbia4, National Radio Astronomy Observatory5, Hillsdale College6, California Institute of Technology7, University of East Anglia8, Université de Montréal9, Vancouver Coastal Health10, Columbia University11, University of Manchester12, Lafayette College13, Australia Telescope National Facility14, Curtin University15, University of Wisconsin–Milwaukee16, University of New Mexico17, Max Planck Society18
TL;DR: In this paper, the authors identify noise in timing residuals that exceeds that predicted for arrival time estimation for millisecond pulsars observed by the North American Nanohertz Observatory for Gravitational Waves.
Abstract: Gravitational wave astronomy using a pulsar timing array requires high-quality millisecond pulsars, correctable interstellar propagation delays, and high-precision measurements of pulse times of arrival. Here we identify noise in timing residuals that exceeds that predicted for arrival time estimation for millisecond pulsars observed by the North American Nanohertz Observatory for Gravitational Waves. We characterize the excess noise using variance and structure function analyses. We find that 26 out of 37 pulsars show inconsistencies with a white-noise-only model based on the short timescale analysis of each pulsar and we demonstrate that the excess noise has a red power spectrum for 15 pulsars. We also decompose the excess noise into chromatic (radio-frequency-dependent) and achromatic components. Associating the achromatic red-noise component with spin noise and including additional power-spectrum-based estimates from the literature, we estimate a scaling law in terms of spin parameters (frequency and frequency derivative) and data-span length and compare it to the scaling law of Shannon \& Cordes (2010). We briefly discuss our results in terms of detection of gravitational waves at nanohertz frequencies.
University of Wisconsin–Milwaukee1, California Institute of Technology2, Lafayette College3, University of Erlangen-Nuremberg4, Goddard Space Flight Center5, Süleyman Demirel University6, West Virginia University7, University of British Columbia8, National Radio Astronomy Observatory9, Hillsdale College10, McGill University11, Columbia University12, Cornell University13, University of Virginia14, United States Naval Research Laboratory15, University of New Mexico16, Max Planck Society17
TL;DR: In this article, the authors present updated radio timing observations along with new and archival optical data that show PSR J1024$-$0719 is most likely in a long period (2$-$20 kyr) binary system with a low-mass ($\approx 0.4\,M_\odot$) low-metallicity ($Z \approx -0.9\,$ dex) main sequence star.
Abstract: PSR J1024$-$0719 is a millisecond pulsar that was long thought to be isolated. However, puzzling results concerning its velocity, distance, and low rotational period derivative have led to reexamination of its properties. We present updated radio timing observations along with new and archival optical data that show PSR J1024$-$0719 is most likely in a long period (2$-$20 kyr) binary system with a low-mass ($\approx 0.4\,M_\odot$) low-metallicity ($Z \approx -0.9\,$ dex) main sequence star. Such a system can explain most of the anomalous properties of this pulsar. We suggest that this system formed through a dynamical exchange in a globular cluster that ejected it into a halo orbit, consistent with the low observed metallicity for the stellar companion. Further astrometric and radio timing observations such as measurement of the third period derivative could strongly constrain the range of orbital parameters.
University of Manchester1, West Virginia University2, Columbia University3, Cornell University4, Oberlin College5, Hillsdale College6, California Institute of Technology7, Goddard Space Flight Center8, University of British Columbia9, National Radio Astronomy Observatory10, Université de Montréal11, Vancouver Coastal Health12, Lafayette College13, University of Virginia14, University of New Mexico15, Max Planck Society16
TL;DR: In this paper, the authors report on an effort to extract and monitor interstellar scintillation parameters in regular timing observations collected for the NANOGrav pulsar timing array, and find estimated scattering delay values that vary with time by up to an order of magnitude.
Abstract: We report on an effort to extract and monitor interstellar scintillation parameters in regular timing observations collected for the NANOGrav 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 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 only a negligible part of their noise budget.