skip to main content

This content will become publicly available on February 1, 2023

Title: The NANOGrav 12.5 yr Data Set: Polarimetry and Faraday Rotation Measures from Observations of Millisecond Pulsars with the Green Bank Telescope
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.
Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more » ; ; ; ; ; ; ; ; ; ; ; « less
Award ID(s):
2020265
Publication Date:
NSF-PAR ID:
10321297
Journal Name:
The Astrophysical Journal
Volume:
926
Issue:
2
ISSN:
0004-637X
Sponsoring Org:
National Science Foundation
More Like this
  1. ABSTRACT Using the first station of the Long Wavelength Array (LWA1), we examine polarized pulsar emission between 25 and 88 MHz. Polarized light from pulsars undergoes Faraday rotation as it passes through the magnetized interstellar medium. Observations from low-frequency telescopes are ideal for obtaining precise rotation measures (RMs) because the effect of Faraday rotation is proportional to the square of the observing wavelength. With these RMs, we obtained polarized pulse profiles to see how polarization changes in the 25–88 MHz range. The RMs were also used to derive values for the electron-density-weighted average Galactic magnetic field along the line of sight. Wemore »present RMs and polarization profiles of 15 pulsars acquired using data from LWA1. These results provide new insight into low-frequency polarization characteristics and pulsar emission heights, and complement measurements at higher frequencies.« less
  2. Abstract We study sky maps and light curves of gamma-ray emission from neutron stars in compact binaries, and in isolation. We briefly review some gamma-ray emission models, and reproduce sky maps from a standard isolated pulsar in the Separatrix Layer model. We consider isolated pulsars with several variations of a dipole magnetic field, including superpositions, and predict their gamma-ray emission. Our results provide new heuristics on what can and cannot be inferred about the magnetic field configuration of pulsars from high-energy observations. We find that typical double-peak light curves can be produced by pulsars with significant multipole structure beyond amore »single dipole. For binary systems, we also present a simple approximation that is useful for rapid explorations of binary magnetic field structure. Finally, we predict the gamma-ray emission pattern from a compact black hole-neutron star binary moments before merger by applying the Separatrix Layer model to data simulated in full general relativity; we find that face-on observers receive little emission, equatorial observers see one broad peak, and more generic observers typically see two peaks.« less
  3. We present wideband (1 − 6.5 GHz) polarimetric observations, obtained with the Karl G. Jansky Very Large Array, of the merging galaxy cluster MACS J0717.5+3745, which hosts one of the most complex known radio relic and halo systems. We used both rotation measure synthesis and QU -fitting to find a reasonable agreement of the results obtained with these methods, particularly when the Faraday distribution is simple and the depolarization is mild. The relic is highly polarized over its entire length (850 kpc), reaching a fractional polarization > 30% in some regions. We also observe a strong wavelength-dependent depolarization for somemore »regions of the relic. The northern part of the relic shows a complex Faraday distribution, suggesting that this region is located in or behind the intracluster medium (ICM). Conversely, the southern part of the relic shows a rotation measure very close to the Galactic foreground, with a rather low Faraday dispersion, indicating very little magnetoionic material intervening along the line of sight. Based on a spatially resolved polarization analysis, we find that the scatter of Faraday depths is correlated with the depolarization, indicating that the tangled magnetic field in the ICM causes the depolarization. We conclude that the ICM magnetic field could be highly turbulent. At the position of a well known narrow-angle-tailed galaxy (NAT), we find evidence of two components that are clearly separated in the Faraday space. The high Faraday dispersion component seems to be associated with the NAT, suggesting the NAT is embedded in the ICM while the southern part of the relic lies in front of it. If true, this implies that the relic and this radio galaxy are not necessarily physically connected and, thus, the relic may, in fact, not be powered by the shock re-acceleration of fossil electrons from the NAT. The magnetic field orientation follows the relic structure indicating a well-ordered magnetic field. We also detected polarized emission in the halo region; however, the absence of significant Faraday rotation and a low value of Faraday dispersion suggests the polarized emission that was previously considered as the part of the halo does, in fact, originate from the shock(s).« less
  4. Abstract We present new discoveries and results from long-term timing of 72 pulsars discovered in the Pulsar Arecibo L -band Feed Array (PALFA) survey, including precise determination of astrometric and spin parameters, and flux density and scatter broadening measurements at 1.4 GHz. Notable discoveries include two young pulsars (characteristic ages ∼30 kyr) with no apparent supernova remnant associations, three mode-changing, 12 nulling and two intermittent pulsars. We detected eight glitches in five pulsars. Among them is PSR J1939+2609, an apparently old pulsar (characteristic age ∼1 Gy), and PSR J1954+2529, which likely belongs to a newly emerging class of binary pulsars.more »The latter is the only pulsar among the 72 that is clearly not isolated: a nonrecycled neutron star with a 931 ms spin period in an eccentric ( e = 0.114) wide ( P b = 82.7 days) orbit with a companion of undetermined nature having a minimum mass of ∼0.6 M ⊙ . Since operations at Arecibo ceased in 2020 August, we give a final tally of PALFA sky coverage, and compare its 207 pulsar discoveries to the known population. On average, they are 50% more distant than other Galactic plane radio pulsars; PALFA millisecond pulsars (MSPs) have twice the dispersion measure per unit spin period than the known population of MSP in the plane. The four intermittent pulsars discovered by PALFA more than double the population of such objects, which should help to improve our understanding of pulsar magnetosphere physics. The statistics for these, rotating radio transients, and nulling pulsars suggest that there are many more of these objects in the Galaxy than was previously thought.« less
  5. Abstract The interstellar medium hosts a population of scattering screens, most of unknown origin. Scintillation studies of pulsars provide a sensitive tool for resolving these scattering screens and a means of measuring their properties. In this paper, we report our analysis of 34 yr of Arecibo observations of PSR B1133 + 16, from which we have obtained high-quality dynamic spectra and their associated scintillation arcs, arising from the scattering screens located along the line of sight to the pulsar. We have identified six individual scattering screens that are responsible for the observed scintillation arcs, which persist for decades. Using themore »assumption that the scattering screens have not changed significantly in this time, we have modeled the variations in arc curvature throughout the Earth’s orbit and extracted information about the placement, orientation, and velocity of five of the six screens, with the highest-precision distance measurement placing a screen at just 5.46 − 0.59 + 0.54 pc from the Earth. We associate the more distant of these screens with an underdense region of the Local Bubble.« less