arXiv subjects

I. H. Stairs

Publications and source records attributed to I. H. Stairs.

At least 19 recordsLinked to original sources

arXiv2026

Timing and statistical analysis of single-pulse search pulsar discoveries from the PALFA survey

Almost two decades after their discovery, pulsars discoverable only through their single, dispersed radio pulses, known as rotating radio transients (RRATS), remain a poorly-understood class of objects. Compared to the overall pulsar population, few have timing solutions, limiting our ability to understand the mechanisms underlying their sporadic emission. Here, we present a single-pulse analysis of twelve sources from the PALFA survey, consisting of eleven objects initially identified as RRATs and one candidate fast radio burst. We present timing solutions for five of the sources with detections at a sufficient number of epochs and spin periods for two more. For all sources, we use a Bayesian framework to fit distributions of single-pulse energies, finding support for log-normal energy distributions and pulse-to-pulse wait times that are consistent with Poisson processes. Finally, we provide updates on the previously-published candidate fast radio burst J0613+18, with new indications that it is in fact extragalactic.

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arXiv2026

Twenty-four thousand hours of GREENBURST observations with the GBT

In addition to fast radio burst (FRB) searches carried out using dedicated surveys, a number of radio observatories take advantage of commensal opportunities with large facilities in which observations for other projects can be searched for FRBs and other transient sources. We present the results from one such effort, the first 24,186 hours of the GREENBURST search for dispersed radio pulses with the Green Bank Telescope (GBT). To date, GREENBURST has detected a total of 50 pulsars and three FRBs. One of the pulsars, PSR J0039+5407, has a period of 2.2 s and was previously unknown. Using follow-up observations with the Canadian Hydrogen Intensity Mapping Experiment, we found a timing solution for this pulsar which shows it to have a characteristic age of 2 Myr. Additional GBT observations show the pulsar has a very high nulling fraction ($\sim70-80\%$). All three of the FRBs are repeating sources that were previously known and were being monitored by the GBT as part of other projects. A major challenge for GREENBURST in the discovery of new FRBs is its single beam. This makes it hard to distinguish some of the pulses from sources of radio frequency interference. We highlight this problem with a case study of an FRB-like pulse that initially passed our interference filters. Upon closer inspection, the event appears to be part of a longer-duration narrow-band source of unknown origin. Further observations and monitoring are required to determine whether it is terrestrial or celestial.

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arXiv2026

Long-term timing of the relativistic binary PSR J1906+0746

We conducted a timing analysis of over 18 years of data on the young ($τ_{\rm c} = 112$ kyr, $P = 114$\,ms) relativistic binary PSR~J1906+0746, using six radio telescopes: Arecibo, FAST, Green Bank, Lovell, MeerKAT, and Nançay. This pulsar is known to orbit a compact high-mass companion with a period of 3.98\,hrs in a mildly eccentric orbit ($e = 0.085$). By combining all data and maintaining a coherent timing solution over the full span, we obtained a more precise measurement of the advance of periastron, $\dotω = 7.5841(2)$\,$°$\,yr$^{-1}$, the Einstein delay, $γ= 4.59(2) \times 10^{-4}$\,s, and the secular change in orbital period, $\dot{P}_{\rm b} = -5.65(2) \times 10^{-13}$\,s\,s$^{-1}$. Assuming the validity of general relativity, we obtain a total mass of 2.6133(1)\,$M_{\odot}$ and component masses of 1.316(5) $M_{\odot}$ for the pulsar and 1.297(5) $M_{\odot}$ for the companion, consistent with a double neutron star system. However, when fitting for the secular change in the projected semi-major axis we obtain $\dot{x} = -1.8(6) \times 10^{-13}$\,s\,s$^{-1}$, the component masses are shifted by $\sim 3.5σ$, which is expected from the correlation of $\dot{x}$ and $γ$. The $\dot{x}$ has a similar magnitude to that observed in PSR~J1141$-$6545, which is due to spin-orbit coupling; if confirmed, it would indicate that, as in the latter system, the companion of the PSR~J1906+0746 system is a massive fast-rotating white dwarf formed before the pulsar. Additionally, we report and characterize a large glitch near MJD 56664, with a fractional frequency increase comparable to those observed in the Vela pulsar.

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arXiv2025

Multi-Method Timing of Transient Radio Pulsars with the GBT350 and GBNCC Surveys

We present the timing solutions for three radio pulsars discovered with the Green Bank North Celestial Cap (GBNCC) and 350-MHz Green Bank Telescope drift-scan surveys. These pulsars were initially discovered through their single-pulse emission and therefore designated as rotating radio transients (RRATs). Follow-up timing campaigns yielded a number of higher signal-to-noise summed pulse profiles for each pulsar, allowing us to obtain timing solutions both through single pulses as well as the standard method of time-integrating the pulsar's emission. We find that the two methods return timing parameters which are usually in agreement within two standard deviations, and have similar sized error bars. The single-pulse timing solutions have significantly higher RMS errors and reduced chi-squared values, likely due to pulse jitter. The distribution of wait times between detected single pulses indicates a significant amount of pulse clustering in time on short timescales from all three sources. For all sources, the presence of low-level emission outside of the sparse bright pulses and lack of giant pulses is more reminiscent of highly nulling canonical radio pulsars than extremely transient RRATs, highlighting the diversity of emission behavior observed from sources published as RRATs.

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arXiv2024

The Green Bank North Celestial Cap Survey IX: Timing Follow-up for 128 Pulsars

The Green Bank North Celestial Cap survey is one of the largest and most sensitive searches for pulsars and transient radio objects. Observations for the survey have finished; priorities have shifted toward long-term monitoring of its discoveries. In this study, we have developed a pipeline to handle large datasets of archival observations and connect them to recent, high-cadence observations taken using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. This pipeline handles data for 128 pulsars and has produced measurements of spin, positional, and orbital parameters that connect data over observation gaps as large as 2000 days. We have also measured glitches in the timing residuals for five of the pulsars included and proper motion for 19 sources (13 new). We include updates to orbital parameters for 19 pulsars, including 9 previously unpublished binaries. For two of these binaries, we provide updated measurements of post-Keplerian binary parameters, which result in much more precise estimates of the total masses of both systems. For PSR J0509+3801, the much improved measurement of the Einstein delay yields much improved mass measurements for the pulsar and its companion, 1.399(6)\Msun and 1.412(6)\Msun, respectively. For this system, we have also obtained a measurement of the orbital decay due to the emission of gravitational waves: $\dot{P}_{\rm B} = -1.37(7)\times10^{-12}$, which is in agreement with the rate predicted by general relativity for these masses.

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arXiv2024

Discovery and timing of ten new millisecond pulsars in the globular cluster Terzan 5

We report the discovery of ten new pulsars in the globular cluster Terzan 5 as part of the Transients and Pulsars with MeerKAT (TRAPUM) Large Survey Project. We observed Terzan 5 at L-band (856--1712 MHz) with the MeerKAT radio telescope for four hours on two epochs, and performed acceleration searches of 45 out of 288 tied-array beams covering the core of the cluster. We obtained phase-connected timing solutions for nine discoveries, covering nearly two decades of archival observations from the Green Bank Telescope for all but one. Highlights include PSR J1748$-$2446ao which is an eccentric ($e = 0.32$) wide-orbit (orbital period $P_{\rm b} = 57.55$ d) system. We were able to measure the rate of advance of periastron ($\dotω$) for this system allowing us to determine a total mass of $3.17 \pm \, 0.02\, \rm M_{\odot}$. With a minimum companion mass ($M_{\rm c}$) of $\sim 0.8\, \rm M_{\odot}$, PSR J1748$-$2446ao is a candidate double neutron star (DNS) system. If confirmed to be a DNS, it would be the fastest spinning pulsar ($P = 2.27$ ms) and the longest orbital period measured for any known DNS system. PSR J1748$-$2446ap has the second highest eccentricity for any recycled pulsar ($e \sim 0.905$) and for this system we can measure the total mass ($1.997 \pm 0.006\, \rm M_{\odot}$) and also estimate the individual pulsar and companion masses. PSR J1748$-$2446ar is an eclipsing redback (minimum $M_{\rm c} \sim 0.34\, \rm M_{\odot}$) system whose properties confirm it to be the counterpart to a previously published source identified in radio and X-ray imaging. With these discoveries, the total number of confirmed pulsars in Terzan 5 is 49, the highest for any globular cluster so far. These discoveries further enhance the rich set of pulsars known in Terzan 5 and provide scope for a deeper understanding of binary stellar evolution, cluster dynamics and ensemble population studies.

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arXiv2024

A MeerKAT view of the double pulsar eclipses -- Geodetic precession of pulsar B and system geometry

The double pulsar system, PSR J0737$-$3039A/B, consists of two neutron stars bound together in a highly relativistic orbit that is viewed nearly edge-on from the Earth. This alignment results in brief radio eclipses of the fast-rotating pulsar A when it passes behind the toroidal magnetosphere of the slow-rotating pulsar B. The morphology of these eclipses is strongly dependent on the geometric orientation and rotation phase of pulsar B, and their time-evolution can be used to constrain the geodetic precession rate of the pulsar. We demonstrate a Bayesian inference framework for modelling eclipse light-curves obtained with MeerKAT between 2019-2023. Using a hierarchical inference approach, we obtained a precession rate of $Ω_{\rm SO}^{\rm B} = {5.16^{\circ}}^{+0.32^{\circ}}_{-0.34^{\circ}}$ yr$^{-1}$ for pulsar B, consistent with predictions from General Relativity to a relative uncertainty of 6.5%. This updated measurement provides a 6.1% test of relativistic spin-orbit coupling in the strong-field regime. We show that a simultaneous fit to all of our observed eclipses can in principle return a $\sim$1.5% test of spin-orbit coupling. However, systematic effects introduced by the current geometric orientation of pulsar B along with inconsistencies between the observed and predicted eclipse light curves result in difficult to quantify uncertainties. Assuming the validity of General Relativity, we definitively show that the spin-axis of pulsar B is misaligned from the total angular momentum vector by $40.6^{\circ} \pm 0.1^{\circ}$ and that the orbit of the system is inclined by approximately $90.5^{\circ}$ from the direction of our line of sight. Our measured geometry for pulsar B suggests the largely empty emission cone contains an elongated horseshoe shaped beam centered on the magnetic axis, and that it may not be re-detected as a radio pulsar until early-2035.

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arXiv2023

The black widow pulsar J1641+8049 in the optical, radio and X-rays

PSR J1641+8049 is a 2 ms black widow pulsar with the 2.2 h orbital period detected in the radio and $γ$-rays. We performed new phase-resolved multi-band photometry of PSR J1641+8049 using the OSIRIS instrument at the Gran Telescopio Canarias. The obtained data were analysed together with the new radio-timing observations from the Canadian Hydrogen Intensity Mapping Experiment (CHIME), the X-ray data from the Spectrum-RG/eROSITA all-sky survey, and all available optical photometric observations. An updated timing solution based on CHIME data is presented, which accounts for secular and periodic modulations in pulse dispersion. The system parameters obtained through the light curve analysis, including the distance to the source 4.6-4.8 kpc and the orbital inclination 56-59 deg, are found to be consistent with previous studies. However, the optical flux of the source at the maximum brightness phase faded by a factor of $\sim$2 as compared to previous observations. Nevertheless, the face of the J1641+8049 companion remains one of the most heated (8000-9500 K) by a pulsar among the known black widow pulsars. We also report a new estimation on the pulsar proper motion of $\approx$2 mas yr$^{-1}$, which yields a spin down luminosity of $\approx$4.87$\times 10^{34}$ ergs s$^{-1}$ and a corresponding heating efficiency of the companion by the pulsar of 0.3-0.7. The pulsar was not detected in X-rays implying its X-ray-luminosity was <3 $\times$ 10$^{31}$ erg s$^{-1}$ at the date of observations.

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arXiv2023

Non-detection of CHIME/FRB sources with the Arecibo Observatory

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 $λ= 10^{-2} - 10^{-1} \text{hr}^{-1}$ 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.

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arXiv2023

Revealing the Dynamic Magneto-ionic Environments of Repeating Fast Radio Burst Sources through Multi-year Polarimetric Monitoring with CHIME/FRB

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 multi-year monitoring with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) over 400-800 MHz. We observe significant RM variations from many sources in our sample, including RM changes of several hundred $\rm{rad\, m^{-2}}$ over month timescales from FRBs 20181119A, 20190303A and 20190417A, and more modest RM variability ($\rm{ΔRM \lesssim}$ few tens rad m$^{-2}$) 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/extreme than those seen from radio pulsars in the Milky Way and the Magellanic Clouds, suggesting repeating FRBs and pulsars occupy distinct magneto-ionic environments.

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arXiv2023

CHIME Discovery of a Binary Pulsar with a Massive Non-Degenerate Companion

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.

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arXiv2022

Gravitational signal propagation in the Double Pulsar studied with the MeerKAT telescope

The Double Pulsar, PSR J0737-3039A/B, has offered a wealth of gravitational experiments in the strong-field regime, all of which GR has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the Double Pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in future, the SKA can greatly improve the accuracy of current tests and facilitate tests of NLO contributions in both orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737-3039A, made using the MeerKAT telescope over the last 3 years. The increased timing precision offered by MeerKAT yields a 2 times better measurement of Shapiro delay parameter s and improved mass measurements compared to previous studies. In addition, our results provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16-yr data by a factor of 1.65. These effects include the retardation effect due to the movement of B and the deflection of the signal by the gravitational field of B. We also investigate novel effects which are expected. For instance, we search for potential profile variations near superior conjunctions caused by shifts of the line-of-sight due to latitudinal signal deflection and find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally, we provide an improved analytical description for the signal propagation in the Double Pulsar system that meets the timing precision expected from future instruments such as the full SKA.

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arXiv2022

A Large Scale Magneto-ionic Fluctuation in the Local Environment of Periodic Fast Radio Burst Source, FRB 20180916B

Fast radio burst (FRB) source 20180916B exhibits a 16.33-day periodicity in its burst activity. It is as of yet unclear what proposed mechanism produces the activity, but polarization information is a key diagnostic. Here, we report on the polarization properties of 44 bursts from FRB 20180916B detected between 2018 December and 2021 December by CHIME/FRB, the FRB project on the Canadian Hydrogen Intensity Mapping Experiment the Canadian Hydrogen Intensity Mapping Experiment. In contrast to previous observations, we find significant variations in the Faraday rotation measure (RM) of FRB 20180916B. Over the nine month period 2021 April$-$2021 December we observe an apparent secular increase in $\rm{RM}$ of $\sim 50 \; \rm{rad\, m^{-2}}$ (a fractional change of over $40\%$) that is accompanied by a possible drift of the emitting band to lower frequencies. This interval displays very little variation in the dispersion measure ($Δ\rm{DM}\lesssim 0.8\; \rm{pc\, cm^{-3}}$) which indicates that the observed RM evolution is likely produced from coherent changes in the Faraday-active medium's magnetic field. Burst-to-burst RM variations appear unrelated to the activity cycle phase. The degree of linear polarization of our burst sample ($\gtrsim 80\%$) is consistent with the negligible depolarization expected for this source in the 400-800 MHz bandpass of CHIME. FRB 20180916B joins other repeating FRBs in displaying substantial RM variations between bursts. This is consistent with the notion that repeater progenitors may be associated with young stellar populations by their preferential occupation of dynamic magnetized environments commonly found in supernova remnants, pulsar wind nebulae or near high mass stellar companions.

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arXiv2022

Discoveries and Timing of Pulsars in NGC 6440

Using the MeerKAT radio telescope, a series of observations have been conducted to time the known pulsars and search for new pulsars in the globular cluster NGC 6440. As a result, two pulsars have been discovered, NGC 6440G and NGC 6440H, one of which is isolated and the other a non-eclipsing (at frequencies above 962 MHz) "Black Widow", with a very low mass companion (M$_{\rm c}$ > 0.006 M$_{\odot}$). It joins the other binary pulsars discovered so far in this cluster which all have low companion masses (M$_{\rm c}$ < 0.30 M$_{\odot}$). We present the results of long-term timing solutions obtained using data from both Green Bank and MeerKAT telescopes for these two new pulsars and an analysis of the pulsars NGC 6440C and NGC 6440D. For the isolated pulsar NGC 6440C, we searched for planets using a Markov Chain Monte Carlo technique. We find evidence for significant unmodelled variations but they cannot be well modelled as planets nor as part of a power-law red-noise process. Studies of the eclipses of the "Redback" pulsar NGC 6440D at two different frequency bands reveal a frequency dependence with longer and asymmetric eclipses at lower frequencies (962-1283 MHz).

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arXiv2022

The eccentric millisecond pulsar, PSR J0955$-$6150 I: Pulse profile analysis, mass measurements and constraints on binary evolution

PSR J0955$-$6150 is a member of a class of eccentric MSP+He WD systems (eMSPs), whose binary evolution is poorly understood and believed to be different to that of traditional MSP+He WD systems. Measuring the masses of the stars in this system is important for testing hypotheses for the formation of eMSPs. We have carried out observations of this pulsar with the Parkes and MeerKAT radio telescopes. Our observations reveal a strong frequency evolution of this pulsar's intensity, with a spectral index ($α$) of $-3.13(2)$. The sensitivity of MeerKAT has resulted in a $>10$-fold improvement in the timing precision compared to older Parkes observations. Combined with the 8-year timing baseline, it has allowed precise measurements of a proper motion and three orbital "post-Keplerian" parameters: the rate of advance of periastron, $\dotω = 0.00152(1) \, {\rm deg} \, yr^{-1}$ and the orthometric Shapiro delay parameters, $h_3 = 0.89(7) \, μ$s and $ς= 0.88(2)$. Assuming general relativity, we obtain $M_{p} = 1.71(2) \, M_{\odot}$ for the mass of the pulsar and $M_{c} = 0.254(2) \, M_{\odot}$ for the mass of the companion; the orbital inclination is 83.2(4) degrees. We find that the spin axis has a misalignment relative to the orbital angular momentum of $> 4.8$ degrees at 99% CI. While the value of $M_{\rm p}$ falls within the wide range observed in eMSPs, $M_{\rm c}$ is significantly smaller than expected, allowing several formation hypotheses being ruled out. $M_{\rm c}$ is also significantly different from the expected value for an ideal low mass X-ray binary evolution scenario. The putative misalignment between the spin axis of the pulsar and the orbital angular momentum suggests that the unknown process that created the orbital eccentricity of the binary was also capable of changing its orbital orientation, an important evidence for understanding the origin of eMSPs.

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arXiv2021

Strong-field Gravity Tests with the Double Pulsar

Continued observations of the Double Pulsar, PSR J0737-3039A/B, consisting of two radio pulsars (A and B) that orbit each other with a period of 2.45hr in a mildly eccentric (e=0.088) binary system, have led to large improvements in the measurement of relativistic effects in this system. With a 16-yr data span, the results enable precision tests of theories of gravity for strongly self-gravitating bodies and also reveal new relativistic effects that have been expected but are now observed for the first time. These include effects of light propagation in strong gravitational fields which are currently not testable by any other method. We observe retardation and aberrational light-bending that allow determination of the pulsar's spin direction. In total, we have detected seven post-Keplerian (PK) parameters, more than for any other binary pulsar. For some of these effects, the measurement precision is so high that for the first time we have to take higher-order contributions into account. These include contributions of A's effective mass loss (due to spin-down) to the observed orbital period decay, a relativistic deformation of the orbit, and effects of the equation of state of super-dense matter on the observed PK parameters via relativistic spin-orbit coupling. We discuss the implications of our findings, including those for the moment of inertia of neutron stars. We present the currently most precise test of general relativity's (GR's) quadrupolar description of gravitational waves, validating GR's prediction at a level of $1.3 \times 10^{-4}$ (95% conf.). We demonstrate the utility of the Double Pulsar for tests of alternative theories by focusing on two specific examples and discuss some implications for studies of the interstellar medium and models for the formation of the Double Pulsar. Finally, we provide context to other types of related experiments and prospects for the future.

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arXiv2021

First discovery of new pulsars and RRATs with CHIME/FRB

We report the discovery of seven new Galactic pulsars with the Canadian Hydrogen Intensity Mapping Experiment's Fast Radio Burst backend (CHIME/FRB). These sources were first identified via single pulses in CHIME/FRB, then followed up with CHIME/Pulsar. Four sources appear to be rotating radio transients (RRATs), pulsar-like sources with occasional single pulse emission with an underlying periodicity. Of those four sources, three have detected periods ranging from 220 ms to 2.726 s. Three sources have more persistent but still intermittent emission and are likely intermittent or nulling pulsars. We have determined phase-coherent timing solutions for the latter three. These seven sources are the first discovery of previously unknown Galactic sources with CHIME/FRB and highlight the potential of fast radio burst detection instruments to search for intermittent Galactic radio sources.

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arXiv2021

Study of 72 pulsars discovered in the PALFA survey: Timing analysis, glitch activity, emission variability, and a pulsar in an eccentric binary

We present new discoveries and results from long-term timing of 72 pulsars discovered in the Arecibo 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 $\sim$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 $\sim$1 Gy), and PSR J1954+2529, which likely belongs to a newly-emerging class of binary pulsars. The latter is the only pulsar among the 72 that is clearly not isolated: a non-recycled neutron star with a 931-ms spin period in an eccentric ($e\,=\,0.114$) wide ($P_b\,=\,82.7\,$d) orbit with a companion of undetermined nature having a minimum mass of $\sim0.6\,M_{\odot}$. 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 (MSP) 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, RRATS, and nulling pulsars suggest that there are many more of these objects in the Galaxy than was previously thought.

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