Dimensions of instruction and assessment were manipulated within a tertiary prevention to examine their effects on word and text reading development. In this article case studies of two children who ...demonstrated significant and sustained lack of adequate response to treatment are profiled. Results indicated that reducing group size, using formative assessment, and implementing mastery learning criteria produced positive trends on indicators of oral reading fluency. Students' reading outcomes provide evidence of the importance of timely data-based instructional adjustments.
In this work, we present follow-up observations of two known repeating fast radio bursts (FRBs) and seven non-repeating FRBs with complex morphology discovered with CHIME/FRB. These observations were ...conducted with the Arecibo Observatory 327 MHz receiver. We detected no additional bursts from these sources, nor did CHIME/FRB detect any additional bursts from these sources during our follow-up program. Based on these non-detections, we provide constraints on the repetition rate, for all nine sources. We calculate repetition rates above 1 Jy using both a Poisson distribution of repetition and the Weibull distribution of repetition presented by Oppermann et al. (2018). For both distributions, we find repetition upper limits of the order \(\lambda = 10^{-2} - 10^{-1} \text{hr}^{-1}\) for all sources. These rates are much lower than those recently published for notable repeating FRBs like FRB 20121102A and FRB 20201124A, suggesting the possibility of a low-repetition sub-population.
Pulsar timing array experiments have recently uncovered evidence for a nanohertz gravitational wave background by precisely timing an ensemble of millisecond pulsars. The next significant milestones ...for these experiments include characterizing the detected background with greater precision, identifying its source(s), and detecting continuous gravitational waves from individual supermassive black hole binaries. To achieve these objectives, generating accurate and precise times of arrival of pulses from pulsar observations is crucial. Incorrect polarization calibration of the observed pulsar profiles may introduce errors in the measured times of arrival. Further, previous studies (e.g., van Straten 2013; Manchester et al. 2013) have demonstrated that robust polarization calibration of pulsar profiles can reduce noise in the pulsar timing data and improve timing solutions. In this paper, we investigate and compare the impact of different polarization calibration methods on pulsar timing precision using three distinct calibration techniques: the Ideal Feed Assumption (IFA), Measurement Equation Modeling (MEM), and Measurement Equation Template Matching (METM). Three NANOGrav pulsars-PSRs J1643\(-\)1224, J1744\(-\)1134, and J1909\(-\)3744-observed with the 800 MHz and 1.5 GHz receivers at the Green Bank Telescope (GBT) are utilized for our analysis. Our findings reveal that all three calibration methods enhance timing precision compared to scenarios where no polarization calibration is performed. Additionally, among the three calibration methods, the IFA approach generally provides the best results for timing analysis of pulsars observed with the GBT receiver system. We attribute the comparatively poorer performance of the MEM and METM methods to potential instabilities in the reference noise diode coupled to the receiver and temporal variations in the profile of the reference pulsar, respectively.
The Canadian Hydrogen Mapping Experiment (CHIME) is a radio telescope located in British Columbia, Canada. The large FOV allows CHIME/FRB to be an exceptional pulsar and Rotating Radio Transient ...(RRAT) finding machine, despite saving only the metadata of incoming Galactic events. We have developed a pipeline to search for pulsar/RRAT candidates using DBSCAN, a clustering algorithm. Follow-up observations are then scheduled with the more sensitive CHIME/Pulsar instrument capable of near-daily high time resolution spectra observations. We have developed the CHIME/Pulsar Single Pulse Pipeline to automate the processing of CHIME/Pulsar search-mode data. We report the discovery of 21 new Galactic sources, with 14 RRATs, 6 isolated long-period pulsars and 1 binary system. Owing to CHIME/Pulsar's observations we have obtained timing solutions for 8 of the 14 RRATs along with all the regular pulsars and the binary system. Notably we report that the binary system is in a long orbit of 412 days with a minimum companion mass of 0.1303 solar masses and no evidence of an optical companion within 10" of the pulsar position. This highlights that working synergistically with CHIME/FRB's large survey volume CHIME/Pulsar can obtain arc second localisations for low burst rate RRATs though pulsar timing. We find that the properties of our newly discovered RRATs are consistent with those of the presently known population. They tend to have lower burst rates than those found in previous surveys, which is likely due to survey bias rather than the underlying population.
Based on the rate of change of its orbital period, PSR J2043+1711 has a
substantial peculiar acceleration of 3.5 $\pm$ 0.8 mm/s/yr, which deviates from
the acceleration predicted by equilibrium Milky ...Way models at a $4\sigma$
level. The magnitude of the peculiar acceleration is too large to be explained
by disequilibrium effects of the Milky Way interacting with orbiting dwarf
galaxies ($\sim$1 mm/s/yr), and too small to be caused by period variations due
to the pulsar being a redback. We identify and examine two plausible causes for
the anomalous acceleration: a stellar flyby, and a long-period orbital
companion. We identify a main-sequence star in \textit{Gaia} DR3 and Pan-STARRS
DR2 with the correct mass, distance, and on-sky position to potentially explain
the observed peculiar acceleration. However, the star and the pulsar system
have substantially different proper motions, indicating that they are not
gravitationally bound. However, it is possible that this is an unrelated star
that just happens to be located near J2043+1711 along our line of sight (chance
probability of 1.6\%). Therefore, we also constrain possible orbital parameters
for a circumbinary companion in a hierarchical triple system with J2043+1711;
the changes in the spindown rate of the pulsar are consistent with an outer
object that has an orbital period of 80 kyr, a companion mass of 0.3 $M_\odot$
(indicative of a white dwarf or low-mass star), and a semi-major axis of 2000
AU. Continued timing and/or future faint optical observations of J2043+1711 may
eventually allow us to differentiate between these scenarios.
Pulsar timing arrays (PTAs) are designed to detect low-frequency
gravitational waves (GWs). GWs induce achromatic signals in PTA data, meaning
that the timing delays do not depend on radio-frequency. ...However, pulse arrival
times are also affected by radio-frequency dependent "chromatic" noise from
sources such as dispersion measure (DM) and scattering delay variations.
Furthermore, the characterization of GW signals may be influenced by the choice
of chromatic noise model for each pulsar. To better understand this effect, we
assess if and how different chromatic noise models affect achromatic noise
properties in each pulsar. The models we compare include existing DM models
used by NANOGrav and noise models used for the European PTA Data Release 2
(EPTA DR2). We perform this comparison using a subsample of six pulsars from
the NANOGrav 15 yr data set, selecting the same six pulsars as from the EPTA
DR2 six-pulsar dataset. We find that the choice of chromatic noise model
noticeably affects the achromatic noise properties of several pulsars. This is
most dramatic for PSR J1713+0747, where the amplitude of its achromatic red
noise lowers from $\log_{10}A_{\text{RN}} = -14.1^{+0.1}_{-0.1}$ to
$-14.7^{+0.3}_{-0.5}$, and the spectral index broadens from $\gamma_{\text{RN}}
= 2.6^{+0.5}_{-0.4}$ to $\gamma_{\text{RN}} = 3.5^{+1.2}_{-0.9}$. We also
compare each pulsar's noise properties with those inferred from the EPTA DR2,
using the same models. From the discrepancies, we identify potential areas
where the noise models could be improved. These results highlight the potential
for custom chromatic noise models to improve PTA sensitivity to GWs.
The millisecond pulsar J1713+0747 underwent a sudden and significant pulse shape change between April 16 and 17, 2021 (MJDs 59320 and 59321). Subsequently, the pulse shape gradually recovered over ...the course of several months. We report the results of continued multi-frequency radio observations of the pulsar made using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the 100-meter Green Bank Telescope (GBT) in a three-year period encompassing the shape change event, between February 2020 and February 2023. As of February 2023, the pulse shape had returned to a state similar to that seen before the event, but with measurable changes remaining. The amplitude of the shape change and the accompanying TOA residuals display a strong non-monotonic dependence on radio frequency, demonstrating that the event is neither a glitch (the effects of which should be independent of radio frequency, \(\nu\)) nor a change in dispersion measure (DM) alone (which would produce a delay proportional to \(\nu^{-2}\)). However, it does bear some resemblance to the two previous "chromatic timing events" observed in J1713+0747 (Demorest et al. 2013; Lam et al. 2016), as well as to a similar event observed in PSR J1643-1224 in 2015 (Shannon et al. 2016).
Noise characterization for pulsar-timing applications accounts for interstellar dispersion by assuming a known frequency-dependence of the delay it introduces in the times of arrival (TOAs). However, ...calculations of this delay suffer from mis-estimations due to other chromatic effects in the observations. The precision in modeling dispersion is dependent on the observed bandwidth. In this work, we calculate the offsets in infinite-frequency TOAs due to mis-estimations in the modeling of dispersion when using varying bandwidths at the Green Bank Telescope. We use a set of broadband observations of PSR J1643-1224, a pulsar with an excess of chromatic noise in its timing residuals. We artificially restricted these observations to a narrowband frequency range, then used both data sets to calculate residuals with a timing model that does not include short-scale dispersion variations. By fitting the resulting residuals to a dispersion model, and comparing the ensuing fitted parameters, we quantify the dispersion mis-estimations. Moreover, by calculating the autocovariance function of the parameters we obtained a characteristic timescale over which the dispersion mis-estimations are correlated. For PSR J1643-1224, which has one of the highest dispersion measures (DM) in the NANOGrav pulsar timing array, we find that the infinite-frequency TOAs suffer from a systematic offset of ~22 microseconds due to DM mis-estimations, with correlations over ~1 month. For lower-DM pulsars, the offset is ~7 microseconds. This error quantification can be used to provide more robust noise modeling in NANOGrav's data, thereby increasing sensitivity and improving parameter estimation in gravitational wave searches.
The cosmic merger history of supermassive black hole binaries (SMBHBs) is expected to produce a low-frequency gravitational wave background (GWB). Here we investigate how signs of the discrete nature ...of this GWB can manifest in pulsar timing arrays through excursions from, and breaks in, the expected \(f_{\mathrm{GW}}^{-2/3}\) power-law of the GWB strain spectrum. To do this, we create a semi-analytic SMBHB population model, fit to NANOGrav's 15 yr GWB amplitude, and with 1,000 realizations we study the populations' characteristic strain and residual spectra. Comparing our models to the NANOGrav 15 yr spectrum, we find two interesting excursions from the power-law. The first, at \(2 \; \mathrm{nHz}\), is below our GWB realizations with \(p\)-value significance \(p = 0.05\) to \(0.06\) (\(\approx 1.8 \sigma - 1.9 \sigma\)). The second, at \(16 \; \mathrm{nHz}\), is above our GWB realizations with \(p = 0.04\) to \(0.15\) (\(\approx 1.4 \sigma - 2.1 \sigma\)). We explore the properties of a loud SMBHB which could cause such an excursion. Our simulations also show that the expected number of SMBHBs decreases by three orders of magnitude, from \(\sim 10^6\) to \(\sim 10^3\), between \(2\; \mathrm{nHz}\) and \(20 \; \mathrm{nHz}\). This causes a break in the strain spectrum as the stochasticity of the background breaks down at \(26^{+28}_{-19} \; \mathrm{nHz}\), consistent with predictions pre-dating GWB measurements. The diminished GWB signal from SMBHBs at frequencies above the \(26\)~nHz break opens a window for PTAs to detect continuous GWs from individual SMBHBs or GWs from the early universe.
Of the more than \(3{,}000\) radio pulsars currently known, only \({\sim}300\) are in binary systems, and only five of these consist of young pulsars with massive non-degenerate companions. We ...present the discovery and initial timing, accomplished using the Canadian Hydrogen Intensity Mapping Experiment telescope (CHIME), of the sixth such binary pulsar, PSR J2108+4516, a \(0.577\)-s radio pulsar in a 269-day orbit of eccentricity 0.09 with a companion of minimum mass \(11\) M\(_{\odot}\). Notably, the pulsar undergoes periods of substantial eclipse, disappearing from the CHIME \(400{-}800\) MHz observing band for a large fraction of its orbit, and displays significant dispersion measure and scattering variations throughout its orbit, pointing to the possibility of a circumstellar disk or very dense stellar wind associated with the companion star. Subarcsecond resolution imaging with the Karl G. Jansky Very Large Array unambiguously demonstrates that the companion is a bright, \(V \simeq 11\) OBe star, EM* UHA 138, located at a distance of \(3.26(14)\) kpc. Archival optical observations of \companion{} approximately suggest a companion mass ranging from \(17.5\) M\(_{\odot} < M_{\rm c} < 23\) M\(_{\odot}\), in turn constraining the orbital inclination angle to \(50.3^{\circ} \lesssim i \lesssim 58.3^{\circ}\). With further multi-wavelength followup, PSR J2108+4516 promises to serve as another rare laboratory for the exploration of companion winds, circumstellar disks, and short-term evolution through extended-body orbital dynamics.
