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Magnetic field values derived from pulsar Faraday RMs superposed on an Aitoff plot of the Galaxy. The color bar at the bottom shows the value of 〈B ∥ 〉 in unit of microGauss. Results from this work are combined with those of Gentile et al. (2018) to get a complete picture of the values around the sky. Note: the plot of Gentile et al. (2018) is incorrect in terms of the sign of the Galactic longitude of the pulsars (which is corrected here).
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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 t...
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... magnetic field value listed is the average over all epochs and both frequencies for each pulsar. Figure 3 shows the value of the magnetic field of pulsars around the sky using the values from this work combined with those of Gentile et al. (2018). The results are consistent with those of Sobey et al. (2019), which uses pulsars and extragalactic sources in the Northern Sky to map the Faraday RMs, and hence the magnetic field of the Galaxy. ...
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We report on the interstellar scintillation from pulsar J2048−1616 for the first time at 732, 1369, and 3100 MHz observed with the Parkes 64 m radio telescope. Dynamic spectra are obtained and diffractive parameters are derived from two-dimensional autocorrelation analyses. The frequency dependencies of the observed diffractive scintillation timesc...
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... Furthermore, Gentile et al. (2018) performed METM polarization calibration on a subset of NANOGrav data observed with the Arecibo Telescope to obtain some of the most sensitive polarimetric MSP profiles. This was repeated for a subset of Green Bank Telescope (GBT) pulsar data in Wahl et al. (2022) where they used MEM calibration method for the polarization calibration. However, a detailed timing analysis with those calibrated profiles have not been done yet (see Wahl (2022) for a precursor work). ...
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.
... We also correct for Faraday rotation using a constant rotation measure (RM) of 9.35 rad m −2 for both observations by applying the corresponding transfer function to the baseband signal, which corrects for the time delays between the left and right circularly polarized signals emitted by the pulsar. The RM was determined by fitting a Faraday rotation curve to the frequency-dependent polarization angle in the folded pulse profile, and is consistent with previous RM measurements (Yan et al. 2011;Dai et al. 2015;Wahl et al. 2022) given the uncertainty introduced by ionospheric contributions. ...
At 327 MHz, the observed emission of PSR B1937+21 is greatly affected by scattering in the interstellar medium, on a timescale of order the pulse period. We use the bright impulsive giant pulses emitted by the pulsar to measure the impulse response of the interstellar medium and then recover the intrinsic emission of the pulsar by deconvolution—revealing fine structure on timescales not normally observable. We find that the intrinsic widths of the main pulse and interpulse in the pulse profile are similar to those measured at higher frequencies. We detect 60,270 giant pulses, which typically appear as narrow, ∼100 ns bursts consisting of one to a few nanoshots with widths ≲ 10 ns. However, about 10% of the giant pulses exhibit multiple bursts that seem to be causally related to each other. We also report the first detection of giant micropulses in PSR B1937+21, primarily associated with the regular main pulse emission. These are distinct from giant pulses not only in the phases at which they occur, but also in their larger widths, of order a microsecond, and steeper energy distribution. These measurements place useful observational constraints on emission mechanisms for giant pulses as well as the regular radio emission of millisecond pulsars.
... It will leverage the novel Radio Camera imaging pipeline for real-time imaging, allowing for efficient processing of fully cross-correlated interferometric data. As a multipurpose observatory, the DSA-2000 has widereaching science applications, including fast radio burst detection and localization, weak lensing studies (Connor et al. 2022), multimessenger astronomy, pulsar timing with NANOGrav (Wahl et al. 2022), and more. We show that it will be a powerful instrument for near-redshift 21 cm intensity mapping. ...
Line-intensity mapping is a promising probe of the Universe’s large-scale structure. We explore the sensitivity of the DSA-2000, a forthcoming array consisting of over 2000 dishes, to the statistical power spectrum of neutral hydrogen’s 21 cm emission line. These measurements would reveal the distribution of neutral hydrogen throughout the near-redshift Universe without necessitating resolving individual sources. The success of these measurements relies on the instrument’s sensitivity and resilience to systematics. We show that the DSA-2000 will have the sensitivity needed to detect the 21 cm power spectrum at z ≈ 0.5 and across power spectrum modes of 0.03–35.12 h Mpc ⁻¹ with 0.1 h Mpc ⁻¹ resolution. We find that supplementing the nominal array design with a dense core of 200 antennas will expand its sensitivity at low power spectrum modes and enable measurement of Baryon Acoustic Oscillations. Finally, we present a qualitative discussion of the DSA-2000's unique resilience to sources of systematic error that can preclude 21 cm intensity mapping.
... For the generation of ToAs, narrow features in the pulse profile can provide strong constraints during template matching (van Straten 2006). Considering that the polarized components of the pulsar profile may exhibit sharp features (e.g., Dai et al. 2015;Wahl et al. 2022), we try to use polarization information to mitigate jitter noise. We perform matrix template matching using all four Stokes parameters (van Straten 2006; Osłowski et al. 2013) to generate frequency-averaged ToAs for each pulsar. ...
Understanding the jitter noise resulting from single-pulse phase and shape variations is important for the detection of gravitational waves using pulsar timing arrays. We present measurements of the jitter noise and single-pulse variability of 12 millisecond pulsars that are part of the International Pulsar Timing Array sample using the Five-hundred-meter Aperture Spherical radio Telescope. We find that the levels of jitter noise can vary dramatically among pulsars. A moderate correlation with a correlation coefficient of 0.57 between jitter noise and pulse width is detected. To mitigate jitter noise, we perform matrix template matching using all four Stokes parameters. Our results reveal a reduction in jitter noise ranging from 6.7% to 39.6%. By performing longitude-resolved fluctuation spectrum analysis, we identify periodic intensity modulations in 10 pulsars. In PSR J0030+0451, we detect single pulses with energies more than 10 times the average pulse energy, suggesting the presence of giant pulses. We also observe a periodic mode-changing phenomenon in PSR J0030+0451. We examine the achievable timing precision by selecting a subset of pulses with a specific range of peak intensity, but no significant improvement in timing precision is achievable.
... By comparing the integrated profiles we obtained at 2250 and 8600 MHz with other available low-frequency results, we will study the profile evolution of these pulsars in a wider frequency range than ever before (e.g., Kramer et al. 1999;Kondratiev et al. 2016). Multifrequency integrated profiles of nine MSPs are presented in Figures 2-10, where low-frequency profiles obtained with other telescopes, including the LOFAR, the Green Bank Telescope (GBT), the Green Bank 140 foot telescope (GB140), the Arecibo 305 m telescope, the Lovell telescope, the Parkes telescope, and the Effelsberg telescope, are taken from the European Pulsar Network (EPN) database 12 , the public Data Archive Portal 13 (Hobbs et al. 2011), and other previously published works (Zhao et al. 2019;Wahl et al. 2022). Since there are no publicly available integrated profiles around 5 GHz for PSRs J0900-3144, J1909-3744, and J1939+2134, we also give their integrated profile plots obtained at 4820 MHz with the TMRT to bridge the large frequency gap from ∼3000-8600 MHz. ...
... The 4820 MHz integrated profile is taken from the archive database of the TMRT by summing seven epochs of observation data (between MJD 59995-60037) with an effective integration time of 16.9 hr. The integrated profiles at other frequencies are taken from Parkes and GBT(Wahl et al. 2022). ...
... The 4820 MHz integrated profile is obtained with the 4 hr observation data on MJD 59762 taken from the archive database of the TMRT. The integrated profiles at other frequencies are taken from Lovell, Parkes(Hobbs et al. 2011;Dai et al. 2015), and GBT(Wahl et al. 2022). estimated flux density results for PSR B0355+54 and target MSPs at 2250 and 8600 MHz (S ν,S and S ν,X ) are listed in Columns(8)and(9) of ...
We report detection results of nine millisecond pulsars (MSPs) at 8600 MHz using simultaneous 2250 and 8600 MHz observations conducted with the Shanghai Tian Ma Radio Telescope. Mainly benefiting from updated ephemerids with 2250 MHz observations, integrated profiles of all nine MSPs at 8600 MHz are successfully obtained by coherently adding multi-epoch (3–83 epochs) observation data spanning from 19–1210 days, which significantly increases the number of MSPs with published profiles (from 4 to 11) above 8000 MHz, as seven of our target MPSs had no related results previously. Combining our new flux density and pulse width measurements with previous low-frequency results, we study their integrated profile evolution and spectral behaviors in a wider frequency range. We find their component separations and pulse widths remain almost constant, which is consistent with previous findings. While dramatic evolution of integrated profiles exists at low frequencies, we observe a potential end of the related evolution around 5 GHz in eight MSPs. The spectra of four MSPs are found to deviate from a single power law, and we fit them with a broken power law. The change in the profile of PSR J1713+0747, which started around MJD 59320−59321, seems to be more prominent as the observation frequency increases. Compared with the effects of the interstellar medium, we prefer to explain this event as some changes in the magnetosphere. We also find its integrated profile possibly had not recovered to the pre-event state until MJD 59842–59857.
... We correct for relative time delays between the left and right circular polarizations of 7.85 ns (MJD 58245) and 37.85 ns (MJD 58298). 1 These delays are dominated by instrumental effects but also include a contribution from circular birefringence in the ISM due to magnetic fields, also known as Faraday rotation, characterized by an RM of ∼7-8 rad m −2 (Yan et al. 2011;Dai et al. 2015;Wahl et al. 2022). ...
Giant pulses emitted by PSR B1937+21 are bright, intrinsically impulsive bursts. Thus, the observed signal from a giant pulse is a noisy but direct measurement of the impulse response from the ionized interstellar medium. We use this fact to detect 13,025 giant pulses directly in the baseband data of two observations of PSR B1937+21. Using the giant pulse signals, we model the time-varying impulse response with a sparse approximation method, in which the time dependence at each delay is decomposed in Fourier components, thus constructing a wavefield as a function of delay and differential Doppler shift. We find that the resulting wavefield has the expected parabolic shape with several diffuse structures within it, suggesting the presence of multiple scattering locations along the line of sight. We also detect an echo at a delay of about 2.4 ms, over 1.5 times the rotation period of the pulsar, which moves along the trajectory expected from geometry between the two observations. The structures in the wavefield are insufficiently sparse to produce a complete model of the system; hence, the model is not predictive across gaps larger than about the scintillation time. Nevertheless, within its range, it reproduces about 75% of the power of the impulse response, a fraction limited mostly by the signal-to-noise ratio of the observations. Furthermore, we show that by deconvolution, using the model impulse response, we can successfully recover the intrinsic pulsar emission from the observed signal.
... In principle, this magnetic field could exist at any point along the LoS. Indeed, multiepoch observations of Galactic pulsars regularly reveal stochastic RM variations that are attributed to scattering and some combination of fluctuations in B ∥ and n e in the Galactic ISM (e.g., Yan et al. 2011;Wahl et al. 2022). However, these RM variations rarely exceed ∼few radians per square meter, significantly less than the RM variability observed from many repeaters reported here. ...
Fast radio bursts (FRBs) display a confounding variety of burst properties and host-galaxy associations. Repeating FRBs offer insight into the FRB population by enabling spectral, temporal, and polarimetric properties to be tracked over time. Here, we report on the polarized observations of 12 repeating sources using multiyear monitoring with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) over 400–800 MHz. We observe significant rotation measure (RM) variations from many sources in our sample, including RM changes of several hundred radians per square meter over month timescales from FRBs 20181119A, 20190303A, and 20190417A, and more modest RM variability (ΔRM ≲ few tens of radians per square meter) from FRBs 20181030A, 20190208A, 20190213B, and 20190117A over equivalent timescales. Several repeaters display a frequency-dependent degree of linear polarization that is consistent with depolarization via scattering. Combining our measurements of RM variations with equivalent constraints on DM variability, we estimate the average line-of-sight magnetic field strength in the local environment of each repeater. In general, repeating FRBs display RM variations that are more prevalent and/or extreme than those seen from radio pulsars in the Milky Way and the Magellanic Clouds, suggesting repeating FRBs and pulsars occupy distinct magnetoionic environments.
... This object is a commonly used calibrator for GBT pulsar observations (see e.g. NANOGrav Collaboration 2015 ; Wahl et al. 2022 ). An on and off source observation of the noise diode was conducted with respect to B1442 + 101 at each observing frequency, once per session. ...
PSR J1757−1854 is one of the most relativistic double neutron star binary systems known in our Galaxy, with an orbital period of Pb = 4.4 hr and an orbital eccentricity of e = 0.61. As such, it has promised to be an outstanding laboratory for conducting tests of relativistic gravity. We present the results of a 6-yr campaign with the 100-m Green Bank and 64-m Parkes radio telescopes, designed to capitalise on this potential. We identify secular changes in the profile morphology and polarisation of PSR J1757−1854, confirming the presence of geodetic precession and allowing the constraint of viewing geometry solutions consistent with General Relativity. We also update PSR J1757−1854’s timing, including new constraints of the pulsar’s proper motion, post-Keplerian parameters and component masses. We conclude that the radiative test of gravity provided by PSR J1757−1854 is fundamentally limited to a precision of 0.3 per cent due to the pulsar’s unknown distance. A search for pulsations from the companion neutron star is also described, with negative results. We provide an updated evaluation of the system’s evolutionary history, finding strong support for a large kick velocity of w ≥ 280 km s−1 following the second progenitor supernova. Finally, we reassess PSR J1757−1854’s potential to provide new relativistic tests of gravity. We conclude that a 3-σ constraint of the change in the projected semi-major axis ($\dot{x}$) associated with Lense-Thirring precession is expected no earlier than 2031. Meanwhile, we anticipate a 3-σ measurement of the relativistic orbital deformation parameter δθ as soon as 2026.
... Different from IPs, some weak emission components were found much closer to the MP in recycled pulsars (i.e., millisecond pulsars, MSPs; Kramer et al. 1998Kramer et al. , 1999Dai et al. 2015;Gentile et al. 2018;Wahl et al. 2022). Such components are called "weak" components (Dai et al. 2015) and "microcomponents" (Gentile et al. 2018;Wahl et al. 2022). ...
... Different from IPs, some weak emission components were found much closer to the MP in recycled pulsars (i.e., millisecond pulsars, MSPs; Kramer et al. 1998Kramer et al. , 1999Dai et al. 2015;Gentile et al. 2018;Wahl et al. 2022). Such components are called "weak" components (Dai et al. 2015) and "microcomponents" (Gentile et al. 2018;Wahl et al. 2022). They are characterized by having a much lower strength compared to the MP. ...
... They are characterized by having a much lower strength compared to the MP. Specifically, "microcomponents" are defined as emission components whose strength is <3% of the highest peak (Wahl et al. 2022). Most "weak" components or "microcomponents" in recycled pulsars appear to be extensions of broad MPs (see Wahl et al. 2022), and some are weak IPs, e.g., the case in PSR J1909-3744 (Dai et al. 2015;Wahl et al. 2022). ...
We discover three new weak pulse components in two known pulsars, one in PSR J0304+1932 and two in PSR J1518+4904. These components are emitted about halfway between the main emission beam and the interpulse beam (beam from the opposite pole). They are separated from their main pulse peak by 99° ± 3° for J0304+1932 and 123.°6 ± 0.°7 (leading) and 93° ± 0.°4 (trailing) for J1518+4904. Their peak-intensity ratios to main pulses are ∼ 0.06% for J0304+1932 and ∼0.17% and ∼0.83% for J1518+4904. We also analyzed the flux fluctuations and profile variations of the emissions for the two pulsars. The results show correlations between the weak pulses and their main pulses, indicating that these emissions come from the same pole. We estimated the emission altitude of these weak pulses and derived a height of about half of the pulsar’s light-cylinder radius. These pulse components are a unique sample of high-altitude emissions from pulsars, and challenge the current pulsar emission models.
... This object is a commonly-used calibrator for GBT pulsar observations (see e.g. NANOGrav Collaboration et al. 2015;Wahl et al. 2022). An on and off source observation of the noise diode was conducted with respect to B1442+101 at each observing frequency, once per session. ...
PSR J1757$-$1854 is one of the most relativistic double neutron star binary systems known in our Galaxy, with an orbital period of $P_\text{b}=4.4\,\text{hr}$ and an orbital eccentricity of $e=0.61$. As such, it has promised to be an outstanding laboratory for conducting tests of relativistic gravity. We present the results of a 6-yr campaign with the 100-m Green Bank and 64-m Parkes radio telescopes, designed to capitalise on this potential. We identify secular changes in the profile morphology and polarisation of PSR J1757$-$1854, confirming the presence of geodetic precession and allowing the constraint of viewing geometry solutions consistent with General Relativity. We also update PSR J1757$-$1854's timing, including new constraints of the pulsar's proper motion, post-Keplerian parameters and component masses. We conclude that the radiative test of gravity provided by PSR J1757$-$1854 is fundamentally limited to a precision of 0.3 per cent due to the pulsar's unknown distance. A search for pulsations from the companion neutron star is also described, with negative results. We provide an updated evaluation of the system's evolutionary history, finding strong support for a large kick velocity of $w\ge280\,\text{km s}^{-1}$ following the second progenitor supernova. Finally, we reassess PSR J1757$-$1854's potential to provide new relativistic tests of gravity. We conclude that a 3-$\sigma$ constraint of the change in the projected semi-major axis ($\dot{x}$) associated with Lense-Thirring precession is expected no earlier than 2031. Meanwhile, we anticipate a 3-$\sigma$ measurement of the relativistic orbital deformation parameter $\delta_\theta$ as soon as 2026.
