arXiv subjects

Andrew Lyne

Publications and source records attributed to Andrew Lyne.

At least 19 recordsLinked to original sources

arXiv2026

The GMRT High-Resolution Southern Sky Survey for pulsars and transients -- VIII: Orbital Variability and the Evolution of a 1-Day He-WD Millisecond Pulsar J2101-4802

We present timing and orbital phase-resolved polarimetry of the millisecond pulsar (MSP) J2101$-$4802, having a spin period of 9.48~ms and dispersion measure (DM) $25.05\ \mathrm{pc\ cm^{-3}}$ discovered with the Giant Meter Radio Telescope (GMRT). From the phase-connected timing of this MSP spanning 3.7 years, we identify that PSR J2101-4802 is in a $\sim$1-day binary orbit with a likely helium-white-dwarf (He-WD) companion having a median companion mass of $\simeq0.15\, M_\odot$, consistent with canonical recycling in the Galactic field. The timing solution further reveals an unusually large orbital period derivative, $\dot{P}_b$ ($\sim10^{-11}\,{\rm s\,s}^{-1}$), compared to typical Galactic-field MSP--HeWD binaries, which cannot be explained by the contributions from kinematic effects (Shklovskii and Galactic acceleration) or general-relativistic damping. Using wideband, full-Stokes observations, we also trace the linear and circular polarization variation across the orbital phase and fit a rotating-vector model (RVM) to its position-angle swing across the pulse phase, yielding constraints on the emission geometry (magnetic inclination and impact angle) of this system. The combination of a $\sim$1-day orbit, $\sim0.15\,M_\odot$ companion, modest spin-down power, unusually large $\dot{P}_b$, and phase-locked magnetized intrabinary plasma signatures suggests that PSR~J2101$-$4802 represents a transitional system linking redback-like spiders to detached He--WD MSP binaries.

astro-ph.HE↗

arXiv2024

A 34 Yr Timing Solution of the Redback Millisecond Pulsar Terzan 5A

We present a 34-year timing solution of the redback pulsar system Terzan 5A (Ter5A). Ter5A, also known as B1744$-$24A or J1748$-$2446A, has a 11.56 ms pulse period, a $\sim$0.1 solar mass dwarf companion star, and an orbital period of 1.82 hours. Ter5A displays highly variable eclipses and orbital perturbations. Using new timing techniques, we have determined a phase-connected timing solution for this system over 34 years. This is the longest ever published for a redback pulsar. We find that the pulsar's spin variability is much larger than most globular cluster pulsars. In fact, of the nine redback pulsars with published or in preparation long-term timing solutions, Ter5A is by far the noisiest. We see no evidence of strong correlations between orbital and spin variability of the pulsar. We also find that long-term astrometric timing measurements are likely too contaminated by this variability to be usable, and therefore require careful short-term timing to determine reasonable positions. Finally, we measure an orbital period contraction of $-2.5(3) \times 10^{-13}$, which is likely dominated by the general relativistic orbital decay of the system. The effects of the orbital variability due to the redback nature of the pulsar are not needed to explain the observed orbital period derivative, but they are constrained to less than $\sim$30% of the observed value.

astro-ph.HE↗

arXiv2024

The GMRT High-Resolution Southern Sky Survey for pulsars and transients -- VII: Timing of Spider MSP J1242-4712, A Bridge Between Redback and Black Widow Pulsars

We present the timing solution for the 5.31-ms spider millisecond pulsar (MSP) J1242-4712, discovered with the GMRT. PSR J1242-4712 orbits a companion of minimum mass 0.08 M$_{\odot}$ with an orbital period of 7.7 hrs and occupies a relatively unexplored region in the orbital period versus companion mass space. We did not detect gamma-ray pulsations for this MSP, and also could not identify the optical counterpart for PSR J1242-4712 in available optical/near-infrared data. The profile of J1242-4712 evolves with frequency showing a clear single component at lower frequencies and a three-component profile at 650 MHz. PSR J1242-4712 eclipses for a very short duration near superior conjunction (orbital phase ~ 0.23-0.25) below 360 MHz. Moreover, significant DM delays and errors in pulse times of arrivals are observed near inferior conjunction (orbital phase ~ 0.7), along with an observed eclipse in one epoch at 650 MHz. Observed eclipses and significant orbital period variability suggest that PSR J1242-4712 is possibly not a He-WD binary, but has a semi or non-degenerate companion, indicating that this is a ``spider" MSP lying in a region between typical black widows and redbacks. This system may represent a distinct category of spider MSPs, displaying characteristics that bridge the gap between known black widow and redback MSPs.

astro-ph.HE↗

arXiv2024

Radio Pulse Profile Evolution of Magnetar Swift J1818.0-1607

The shape and polarisation properties of the radio pulse profiles of radio-loud magnetars provide a unique opportunity to investigate their magnetospheric properties. Gaussian Process Regression analysis was used to investigate the variation in the total intensity shape of the radio pulse profiles of the magnetar Swift J1818.0-1607. The observed profile shape was found to evolve through three modes between MJDs 59104 and 59365. The times at which these transitions occurred coincided with changes in the amplitude of modulations in the spin-down rate. The amount of linear and circular polarisation was also found to vary significantly with time. Lomb-Scargle periodogram analysis of the spin-down rate revealed three possibly harmonically related frequencies. This could point to the magnetar experiencing seismic activity. However, no profile features exhibited significant periodicity, suggesting no simple correlations between the profile variability and fluctuations of the spin-down on shorter timescales within the modes. Overall, this implies the mode changes seen are a result of local magnetospheric changes, with other theories, such as precession, less able to explain these observations.

astro-ph.HE↗

arXiv2023

Search for gravitational wave signals from known pulsars in LIGO-Virgo O3 data using the 5n-vector ensemble method

The 5n-vector ensemble method is a multiple test for the targeted search of continuous gravitational waves from an ensemble of known pulsars. This method can improve the detection probability combining the results from individually undetectable pulsars if few signals are near the detection threshold. In this paper, we apply the 5n-vector ensemble method to the O3 data set from the LIGO and Virgo detectors considering an ensemble of 201 known pulsars. We find no evidence for a signal from the ensemble and set a 95% credible upper limit on the mean ellipticity assuming a common exponential distribution for the pulsars' ellipticities. Using two independent hierarchical Bayesian procedures, we find upper limits of $1.2 \times 10^{-9}$ and $2.5 \times 10^{-9}$ on the mean ellipticity for the 201 analyzed pulsars.

gr-qc↗

arXiv2023

The Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars

We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems co-located with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to $\leq 11$ known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with 6 undetected in radio. Overall, >235 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power $\dot E$ decreases to its observed minimum near $10^{33}$ erg s$^{-1}$, approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties and fit results to guide and be compared with modeling results.

astro-ph.HE↗

arXiv2022

Discovery, Timing, and Multiwavelength Observations of the Black Widow Millisecond Pulsar PSR J1555-2908

We report the discovery of PSR J1555-2908, a 1.79 ms radio and gamma-ray pulsar in a 5.6 hr binary system with a minimum companion mass of 0.052 $M_\odot$. This fast and energetic ($\dot E = 3 \times 10^{35}$ erg/s) millisecond pulsar was first detected as a gamma-ray point source in Fermi LAT sky survey observations. Guided by a steep spectrum radio point source in the Fermi error region, we performed a search at 820 MHz with the Green Bank Telescope that first discovered the pulsations. The initial radio pulse timing observations provided enough information to seed a search for gamma-ray pulsations in the LAT data, from which we derive a timing solution valid for the full Fermi mission. In addition to the radio and gamma-ray pulsation discovery and timing, we searched for X-ray pulsations using NICER but no significant pulsations were detected. We also obtained time-series r-band photometry that indicates strong heating of the companion star by the pulsar wind. Material blown off the heated companion eclipses the 820 MHz radio pulse during inferior conjunction of the companion for ~10% of the orbit, which is twice the angle subtended by its Roche lobe in an edge-on system.

astro-ph.HE↗

arXiv2021

The orbital-decay test of general relativity to the 2% level with 6-year VLBA astrometry of the double neutron star PSR J1537+1155

PSR J1537+1155, also known as PSR B1534+12, is the second discovered double neutron star (DNS) binary. More than 20 years of timing observations of PSR J1537+1155 have offered some of the most precise tests of general relativity (GR) in the strong-field regime. As one of these tests, the gravitational-wave emission predicted by GR has been probed with the significant orbital decay ($\dot{P}_\mathrm{b}$) of PSR J1537+1155. However, compared to most GR tests provided with the post-Keplerian parameters, the orbital-decay test was lagging behind in terms of both precision and consistency with GR, limited by the uncertain distance of PSR J1537+1155. With an astrometric campaign spanning 6 years using the Very Long Baseline Array, we measured an annual geometric parallax of $1.063\pm0.075$ mas for PSR J1537+1155, corresponding to a distance of $0.94^{+0.07}_{-0.06}$ kpc. This is the most tightly-constrained model-independent distance achieved for a DNS to date. After obtaining $\dot{P}_\mathrm{b}^\mathrm{Gal}$ (i.e., the orbital decay caused by Galactic gravitational potential) with a combination of 4 Galactic mass distribution models, we updated the ratio of the observed intrinsic orbital decay to the GR prediction to $0.977\pm0.020$, three times more precise than the previous orbital-decay test ($0.91\pm0.06$) made with PSR J1537+1155.

astro-ph.HE↗

arXiv2019

Radio emission from a pulsar's magnetic pole revealed by general relativity

Binary pulsars are affected by general relativity (GR), causing the spin axes of each pulsar to precess. We present polarimetric radio observations of PSR J1906+0746 that demonstrate the validity of the geometrical model of pulsar polarisation. We reconstruct the (sky-projected) polarisation emission map over the pulsar's magnetic pole and predict the disappearance of the detectable emission by 2028. Two additional tests of GR are performed in this system, including the spin-precession for strongly self-gravitating bodies. We constrain the relativistic treatment of the pulsar polarisation model and measure the pulsar beaming fraction, with implications for the population of neutron stars and the expected rate of neutron star mergers.

astro-ph.HE↗

arXiv2017

Large magnetic field variations towards the Galactic Centre magnetar, PSR J1745-2900

Polarised radio emission from PSR J1745-2900 has already been used to investigate the strength of the magnetic field in the Galactic Centre, close to Sagittarius A*. Here we report how persistent radio emission from this magnetar, for over four years since its discovery, has revealed large changes in the observed Faraday rotation measure, by up to 3500 rad m$^{-2}$ (a five per cent fractional change). From simultaneous analysis of the dispersion measure, we determine that these fluctuations are dominated by variations in the projected magnetic field, rather than the integrated free electron density, along the changing line of sight to the rapidly moving magnetar. From a structure function analysis of rotation measure variations, and a recent epoch of rapid change of rotation measure, we determine a minimum scale of magnetic fluctuations of size ~ 2 au at the Galactic Centre distance, inferring PSR J1745-2900 is just ~ 0.1 pc behind an additional scattering screen.

astro-ph.HE↗

arXiv2015

The Binary Nature of PSR J2032+4127

PSR J2032+4127 is a gamma-ray and radio-emitting pulsar which has been regarded as a young luminous isolated neutron star. However, its recent spin-down rate has extraordinarily increased by a factor of two. We present evidence that this is due to its motion as a member of a highly-eccentric binary system with a 15-solar-mass Be star, MT91~213. Timing observations show that, not only are the positions of the two stars coincident within 0.4 arcsec, but timing models of binary motion of the pulsar fit the data much better than a model of a young isolated pulsar. MT91~213, and hence the pulsar, lie in the Cyg~OB2 stellar association, which is at a distance of only 1.4-1.7 kpc. The pulsar is currently on the near side of, and accelerating towards, the Be star, with an orbital period of 20-30 years. The next periastron is well-constrained to occur in early 2018, providing an opportunity to observe enhanced high-energy emission as seen in other Be-star binary systems.

astro-ph.HE↗

arXiv2014

45 Years of Rotation of the Crab Pulsar

The 30-Hz rotation rate of the Crab pulsar has been monitored at Jodrell Bank Observatory since 1984 and by other observatories before then. Since 1968, the rotation rate has decreased by about $0.5$\,Hz, interrupted only by sporadic and small spin up events (glitches). 24 of these events have been observed, including a significant concentration of 15 occurring over an interval of 11 years following MJD 50000. The monotonic decrease of the slowdown rate is partially reversed at glitches. This reversal comprises a step and an asymptotic exponential with a 320-day time constant, as determined in the three best-isolated glitches. The cumulative effect of all glitches is to reduce the decrease in slowdown rate by about 6\%. Overall, a low mean braking index of $2.342(1)$ is measured for the whole period, compared with values close to $2.5$ in intervals between glitches. Removing the effects of individual glitches reveals an underlying power law slowdown with the same braking index of 2.5. We interpret this value in terms of a braking torque due to a dipolar magnetic field in which the inclination angle between the dipole and rotation axes is increasing. There may also be further effects due to a monopolar particle wind or infalling supernova debris.

astro-ph.HE↗

arXiv2013

Long-Term Radio Timing Observations of the Transition Millisecond Pulsar PSR~J1023+0038

The radio millisecond pulsar PSR J1023+0038 exhibits complex timing and eclipse behavior. Here we analyze four years' worth of radio monitoring observations of this object. We obtain a long-term timing solution, albeit with large residual timing errors as a result of apparent orbital period variations. We also observe variable eclipses when the companion passes near our line of sight, excess dispersion measure near the eclipses and at random orbital phases, and short-term disappearances of signal at random orbital phases. We interpret the eclipses as possibly due to material in the companion's magnetosphere supported by magnetic pressure, and the orbital period variations as possibly due to a gravitational quadrupole coupling mechanism. Both of these mechanisms would be the result of magnetic activity in the companion, in conflict with evolutionary models that predict it should be fully convective and hence non-magnetic. We also use our timing data to test for orbital and rotational modulation of the system's $γ$-ray emission, finding no evidence for orbital modulation and $3.7σ$ evidence for modulation at the pulsar period. The energetics of the system make it plausible that the $γ$-ray emission we observe is entirely from the millisecond pulsar itself, but it seems unlikely for these $γ$-rays to provide the irradiation of the companion, which we attribute instead to X-ray heating from a shock powered by a particle wind.

astro-ph.HE↗

arXiv2013

Evolution of the Magnetic Field Structure of the Crab Pulsar

Pulsars are highly-magnetised rotating neutron stars and are well-known for the stability of their signature pulse shapes, allowing high-precision studies of their rotation. However, during the past 22 years, the radio pulse profile of the Crab pulsar has shown a steady increase in the separation of the main pulse and interpulse components at 0.62$^{\rm o}\pm$0.03$^{\rm o}$ per century. There are also secular changes in the relative strengths of several components of the profile. The changing component separation indicates that the axis of the dipolar magnetic field, embedded in the neutron star, is moving towards the stellar equator. This evolution of the magnetic field could explain why the pulsar does not spin down as expected from simple braking by a rotating dipolar magnetic field.

astro-ph.HE↗

arXiv2013

Simultaneous X-ray and Radio Observations of Rotating Radio Transient J1819-1458

We present the results of simultaneous radio and X-ray observations of PSR J1819-1458. Our 94-ks XMM-Newton observation of the high magnetic field 5*10^13 G pulsar reveals a blackbody spectrum (kT~130 eV) with a broad absorption feature, possibly composed of two lines at ~1.0 and ~1.3 keV. We performed a correlation analysis of the X-ray photons with radio pulses detected in 16.2 hours of simultaneous observations at 1-2 GHz with the Green Bank, Effelsberg, and Parkes telescopes, respectively. Both the detected X-ray photons and radio pulses appear to be randomly distributed in time. We find tentative evidence for a correlation between the detected radio pulses and X-ray photons on timescales of less than 10 pulsar spin periods, with the probability of this occurring by chance being 0.46%. This suggests that the physical process producing the radio pulses may also heat the polar-cap.

astro-ph.SR↗

arXiv2012

Timing noise and the long-term stability of pulsar profiles

It has recently been shown that there is a close correlation between the slowdown rates and the pulse shapes of six pulsars, and between the slowdown rates and the flux density of three others. This indicates that these phenomena are related by changes in the current flows in the pulsar magnetospheres. In this paper we review the observational status of these studies, which have now been extended to a total of 16 pulsars having correlated slowdown and pulse emission properties. The changes seem to be due to sudden switching between just two discrete magnetospheric states in the well-known processes of mode-changing and pulse nulling. We also address how widespread these phenomena are in the wider pulsar population.

astro-ph.HE↗

arXiv2011

The braking index of PSR J1734-3333 and the magnetar population

PSR J1734-3333 is a radio pulsar rotating with a period P=1.17 s and slowing down with a period derivative Pdot=2.28 x 10^{-12}, the third largest among rotation-powered pulsars. These properties are midway between those of normal rotation-powered pulsars and magnetars, two populations of neutron stars that are notably different in their emission properties. Here we report on the measurement of the second period derivative of the rotation of PSR J1734-3333 and calculate a braking index n=0.9 +- 0.2. This value is well below 3, the value expected for an electromagnetic braking due to a constant magnetic dipole, and indicates that this pulsar may soon have the rotational properties of a magnetar. While there are several mechanisms which could lead to such a low braking index, we discuss this observation, together with the properties exhibited by some other high-Pdot rotation-powered pulsars, and interpret it as evidence of a possible evolutionary route for magnetars through a radio-pulsar phase, supporting a unified description of the two classes of object.

astro-ph.HE↗

arXiv2011

Radio Properties of Rotating Radio Transients I: searches for periodicities and randomness in pulse arrival times

We have analysed the long- and short-term time dependence of the pulse arrival times and the pulse detection rates for eight Rotating Radio Transient (RRAT) sources from the Parkes Multi-beam Pulsar Survey (PMPS). We find significant periodicities in the individual pulse arrival times from six RRATs. These periodicities range from 30 minutes to 2100 days and from one to 16 independent (i.e. non-harmonically related) periodicities are detected for each RRAT. In addition, we find that pulse emission is a random (i.e. Poisson) process on short (hour-long) time scales but that most of the objects exhibit longer term (months-years) non-random behaviour. We find that PSRs J1819-1458 and J1317-5759 emit more doublets (two consecutive pulses) and triplets (three consecutive pulses) than is expected in random pulse distributions. No evidence for such an excess is found for the other RRATs. There are several different models for RRAT emission depending on both extrinsic and intrinsic factors which are consistent with these properties.

astro-ph.SR↗