arXiv subjects

M. A. McLaughlin

Publications and source records attributed to M. A. McLaughlin.

At least 145 records · Page 8Linked to original sources

arXiv2012

A parallax distance and mass estimate for the transitional millisecond pulsar system J1023+0038

The recently discovered transitional millisecond pulsar system J1023+0038 exposes a crucial evolutionary phase of recycled neutron stars for multiwavelength study. The system, comprising the neutron star itself, its stellar companion, and the surrounding medium, is visible across the electromagnetic spectrum from the radio to X-ray/gamma-ray regimes and offers insight into the recycling phase of millisecond pulsar evolution. Here, we report on multiple-epoch astrometric observations with the Very Long Baseline Array (VLBA) which give a system parallax of 0.731 +/- 0.022 milliarcseconds (mas) and a proper motion of 17.98 +/- 0.05 mas/yr. By combining our results with previous optical observations, we are able to use the parallax distance of 1368+42-39 pc to estimate the mass of the pulsar as 1.71 +/- 0.16 solar masses, and we are also able to measure the 3D space velocity of the system as 126 +/- 5 km/s. Despite the precise nature of the VLBA measurements, the remaining ~3% distance uncertainty dominates the 0.16 solar mass error on our mass estimate.

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arXiv2012

Discovery of the Optical/Ultraviolet/Gamma-ray Counterpart to the Eclipsing Millisecond Pulsar J1816+4510

The energetic, eclipsing millisecond pulsar J1816+4510 was recently discovered in a low-frequency radio survey with the Green Bank Telescope. With an orbital period of 8.7 hr and minimum companion mass of 0.16 Msun it appears to belong to an increasingly important class of pulsars that are ablating their low-mass companions. We report the discovery of the gamma-ray counterpart to this pulsar, and present a likely optical/ultraviolet counterpart as well. Using the radio ephemeris we detect pulsations in the unclassified gamma-ray source 2FGL J1816.5+4511, implying an efficiency of ~25% in converting the pulsar's spin-down luminosity into gamma-rays and adding PSR J1816+4510 to the large number of millisecond pulsars detected by Fermi. The likely optical/UV counterpart was identified through position coincidence (<0.1") and unusual colors. Assuming that it is the companion, with R=18.27+/-0.03 mag and effective temperature >15,000 K it would be among the brightest and hottest of low-mass pulsar companions, and appears qualitatively different from other eclipsing pulsar systems. In particular, current data suggest that it is a factor of two larger than most white dwarfs of its mass, but a factor of four smaller than its Roche lobe. We discuss possible reasons for its high temperature and odd size, and suggest that it recently underwent a violent episode of mass loss. Regardless of origin, its brightness and the relative unimportance of irradiation make it an ideal target for a mass, and hence a neutron star mass, determination.

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arXiv2012

Radio Searches of Fermi LAT Sources and Blind Search Pulsars: The Fermi Pulsar Search Consortium

We present a summary of the Fermi Pulsar Search Consortium (PSC), an international collaboration of radio astronomers and members of the Large Area Telescope (LAT) collaboration, whose goal is to organize radio follow-up observations of Fermi pulsars and pulsar candidates among the LAT gamma-ray source population. The PSC includes pulsar observers with expertise using the world's largest radio telescopes that together cover the full sky. We have performed very deep observations of all 35 pulsars discovered in blind frequency searches of the LAT data, resulting in the discovery of radio pulsations from four of them. We have also searched over 300 LAT gamma-ray sources that do not have strong associations with known gamma-ray emitting source classes and have pulsar-like spectra and variability characteristics. These searches have led to the discovery of a total of 43 new radio millisecond pulsars (MSPs) and four normal pulsars. These discoveries greatly increase the known population of MSPs in the Galactic disk, more than double the known population of so-called `black widow' pulsars, and contain many promising candidates for inclusion in pulsar timing arrays.

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arXiv2012

PSR J0737-3039B: A probe of radio pulsar emission heights

In the double pulsar system PSR J0737-3039A/B the strong wind produced by pulsar A distorts the magnetosphere of pulsar B. The influence of these distortions on the orbital-dependent emission properties of pulsar B can be used to determine the location of the coherent radio emission generation region in the pulsar magnetosphere. Using a model of the wind-distorted magnetosphere of pulsar B and the well defined geometrical parameters of the system, we determine the minimum emission height to be ~ 20 neutron star radii in the two bright orbital longitude regions. We can determine the maximum emission height by accounting for the amount of deflection of the polar field line with respect to the magnetic axis using the analytical magnetic reconnection model of Dungey and the semi-empirical numerical model of Tsyganenko. Both of these models estimate the maximum emission height to be ~ 2500 neutron star radii. The minimum and maximum emission heights we calculate are consistent with those estimated for normal isolated pulsars.

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arXiv2012

Practical Methods for Continuous Gravitational Wave Detection using Pulsar Timing Data

Gravitational Waves (GWs) are tiny ripples in the fabric of space-time predicted by Einstein's General Relativity. Pulsar timing arrays (PTAs) are well poised to detect low frequency ($10^{-9}$ -- $10^{-7}$ Hz) GWs in the near future. There has been a significant amount of research into the detection of a stochastic background of GWs from supermassive black hole binaries (SMBHBs). Recent work has shown that single continuous sources standing out above the background may be detectable by PTAs operating at a sensitivity sufficient to detect the stochastic background. The most likely sources of continuous GWs in the pulsar timing frequency band are extremely massive and/or nearby SMBHBs. In this paper we present detection strategies including various forms of matched filtering and power spectral summing. We determine the efficacy and computational cost of such strategies. It is shown that it is computationally infeasible to use an optimal matched filter including the poorly constrained pulsar distances with a grid based method. We show that an Earth-term-matched filter constructed using only the correlated signal terms is both computationally viable and highly sensitive to GW signals. This technique is only a factor of two less sensitive than the computationally unrealizable optimal matched filter and a factor of two more sensitive than a power spectral summing technique. We further show that a pairwise matched filter, taking the pulsar distances into account is comparable to the optimal matched filter for the single template case and comparable to the Earth-term-matched filter for many search templates. Finally, using simulated data optimal quality, we place a theoretical minimum detectable strain amplitude of $h>2\times 10^{-15}$ from continuous GWs at frequencies on the order $\sim1/T_{\rm obs}$.

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arXiv2012

Correlation of Chandra photons with the radio giant pulses from the Crab pulsar

No apparent correlation was found between giant pulses (GPs) and X-ray photons from the Crab pulsar during 5.4 hours of simultaneous observations with the Green Bank Telescope at 1.5 GHz and Chandra X-Ray Observatory primarily in the energy range 1.5-4.5 keV. During the Crab pulsar periods with GPs the X-ray flux in radio emission phase windows does not change more than by +-10% for main pulse (MP) GPs and +-30% for interpulse (IP) GPs. During giant pulses themselves, the X-ray flux does not change more than by two times for MP GPs and 5 times for IP GPs. All limits quoted are compatible with 2-sigma fluctuations of the X-ray flux around the sets of false GPs with random arrival times. The results speak in favor of changes in plasma coherence as the origin of GPs. However, the results do not rule out variations in the rate of particle creation if the particles that emit coherent radio emission are mostly at the lowest Landau level.

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arXiv2012

The Double Pulsar Eclipses I: Phenomenology and Multi-frequency Analysis

The double pulsar PSR J0737-3039A/B displays short, 30 s eclipses that arise around conjunction when the radio waves emitted by pulsar A are absorbed as they propagate through the magnetosphere of its companion pulsar B. These eclipses offer a unique opportunity to probe directly the magnetospheric structure and the plasma properties of pulsar B. We have performed a comprehensive analysis of the eclipse phenomenology using multi-frequency radio observations obtained with the Green Bank Telescope. We have characterized the periodic flux modulations previously discovered at 820 MHz by McLaughlin et al., and investigated the radio frequency dependence of the duration and depth of the eclipses. Based on their weak radio frequency evolution, we conclude that the plasma in pulsar B's magnetosphere requires a large multiplicity factor (~ 10^5). We also found that, as expected, flux modulations are present at all radio frequencies in which eclipses can be detected. Their complex behavior is consistent with the confinement of the absorbing plasma in the dipolar magnetic field of pulsar B as suggested by Lyutikov & Thompson and such a geometric connection explains that the observed periodicity is harmonically related to pulsar B's spin frequency. We observe that the eclipses require a sharp transition region beyond which the plasma density drops off abruptly. Such a region defines a plasmasphere which would be well inside the magnetospheric boundary of an undisturbed pulsar. It is also two times smaller than the expected standoff radius calculated using the balance of the wind pressure from pulsar A and the nominally estimated magnetic pressure of pulsar B.

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arXiv2011

Discovery of Nine Gamma-Ray Pulsars in Fermi-LAT Data Using a New Blind Search Method

We report the discovery of nine previously unknown gamma-ray pulsars in a blind search of data from the Fermi Large Area Telescope (LAT). The pulsars were found with a novel hierarchical search method originally developed for detecting continuous gravitational waves from rapidly rotating neutron stars. Designed to find isolated pulsars spinning at up to kHz frequencies, the new method is computationally efficient, and incorporates several advances, including a metric-based gridding of the search parameter space (frequency, frequency derivative and sky location) and the use of photon probability weights. The nine pulsars have spin frequencies between 3 and 12 Hz, and characteristic ages ranging from 17 kyr to 3 Myr. Two of them, PSRs J1803-2149 and J2111+4606, are young and energetic Galactic-plane pulsars (spin-down power above 6e35 erg/s and ages below 100 kyr). The seven remaining pulsars, PSRs J0106+4855, J0622+3749, J1620-4927, J1746-3239, J2028+3332, J2030+4415, J2139+4716, are older and less energetic; two of them are located at higher Galactic latitudes (|b| > 10 deg). PSR J0106+4855 has the largest characteristic age (3 Myr) and the smallest surface magnetic field (2e11 G) of all LAT blind-search pulsars. PSR J2139+4716 has the lowest spin-down power (3e33 erg/s) among all non-recycled gamma-ray pulsars ever found. Despite extensive multi-frequency observations, only PSR J0106+4855 has detectable pulsations in the radio band. The other eight pulsars belong to the increasing population of radio-quiet gamma-ray pulsars.

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arXiv2011

Rotating Radio Transients

Over the past several years, it has become apparent that some radio pulsars demonstrate significant variability in their single pulse amplitude distributions. The Rotating Radio Transients (RRATs), pulsars discovered through their single, isolated pulses, are one of the more extreme manifestations of this variability. Nearly 70 of these objects have been found over the past several years in archival and new pulsar surveys. In this review, we describe these searches and their resulting discoveries. We then discuss radio timing algorithms and the spin-down properties of the 19 RRATs with phase-connected solutions. The spin-down parameters fall within the same range as other pulsars, with a tendency towards longer periods and higher magnetic fields. Next we describe follow-up observations at radio wavelengths. These show that there are periodic fluctuations in the pulse detection rates of some RRATs and that RRATs in general have similar spectra to other pulsars. X-ray detection has only been made for one RRAT, J1819-1458; observations have revealed absorption features and a bright X-ray nebula. Finally, we look to future telescopes and the progress that will be made with these in characterising and understanding the Galactic RRAT population.

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arXiv2011

The impact of a stochastic gravitational-wave background on pulsar timing parameters

Gravitational waves are predicted by Einstein's theory of general relativity as well as other theories of gravity. The rotational stability of the fastest pulsars means that timing of an array of these objects can be used to detect and investigate gravitational waves. Simultaneously, however, pulsar timing is used to estimate spin period, period derivative, astrometric, and binary parameters. Here we calculate the effects that a stochastic background of gravitational waves has on pulsar timing parameters through the use of simulations and data from the millisecond pulsars PSR J0437--4715 and PSR J1713+0747. We show that the reported timing uncertainties become underestimated with increasing background amplitude by up to a factor of $\sim10$ for a stochastic gravitational-wave background amplitude of $A=5\times 10^{-15}$, where $A$ is the amplitude of the characteristic strain spectrum at one-year gravitational wave periods. We find evidence for prominent low-frequency spectral leakage in simulated data sets including a stochastic gravitational-wave background. We use these simulations along with independent Very Long Baseline Interferometry (VLBI) measurements of parallax to set a 2--sigma upper limit of $A\le9.1\times 10^{-14}$. We find that different supermassive black hole assembly scenarios do not have a significant effect on the calculated upper limits. We also test the effects that ultralow--frequency (10$^{-12}$--10$^{-9}$ Hz) gravitational waves have on binary pulsar parameter measurements and find that the corruption of these parameters is less than those due to $10^{-9}$--$10^{-7}$ Hz gravitational waves.

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arXiv2011

Chandra Observations of the High-Magnetic-Field Radio Pulsar J1718-3718

High-magnetic-field pulsars represent an important class of objects for studying the relationship between magnetars and radio pulsars. Here we report on four Chandra observations of the high-magnetic-field pulsar J1718-3718 ($B=7.4\times10^{13}$\,G) taken in 2009 as well as on a re-analysis of 2002 Chandra observations of the region. We also report an improved radio position for this pulsar based on ATCA observations. We detect X-ray pulsations at the pulsar's period in the 2009 data, with pulsed fraction 52%$\pm$13% in the 0.8--2.0 keV band. We find that the X-ray pulse is aligned with the radio pulse. The data from 2002 and 2009 show consistent spectra and fluxes; a merged overall spectrum is well fit by a blackbody of temperature $186^{+19}_{-18}$\,eV, slightly higher than predicted by standard cooling models, however, the best-fit neutron star atmosphere model is consistent with standard cooling. We find the bolometric luminosity $L^{\infty}_{\rm bb}=4^{+5}_{-2} \times10^{32}$\,erg\,s$^{-1}\sim0.3\dot{E}$, for a distance of 4.5 kpc. We compile measurements of the temperatures of all X-ray detected high-$B$ pulsars as well as those of low-$B$ radio pulsars and find evidence for the former being on average hotter than the latter.

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arXiv2011

An Arecibo Search for Pulsars and Transient Sources in M33

We report on a systematic and sensitive search for pulsars and transient sources in the nearby spiral galaxy M33, conducted at 1.4 GHz with the Arecibo telescope's seven-beam receiver system, ALFA. Data were searched for both periodic and aperiodic sources, up to 1000 pc cm^{-3} in dispersion measure and on timescales from $\sim$50 \us to several seconds. The galaxy was sampled with 12 ALFA pointings, or 84 pixels in total, each of which was searched for 2-3 hr. We describe the observations, search methodologies and analysis strategies applicable to multibeam systems, and comment on the data quality and statistics of spurious events that arise due to radio frequency interference. While these searches have not led to any conclusive signals of periodic or transient nature that originate in the galaxy, they illustrate some of the underlying challenges and difficulties in such searches and the efficacy of simultaneous multiple beams in the analysis of search output. The implied limits are $\la$5 uJy Mpc^2 in luminosity (at 1400 MHz) for periodic sources in M33 with duty cycles $\la$5%. For short-duration transient signals (with pulse widths $\la$100 \us), the limiting peak flux density is 100 mJy, which would correspond to a 5-$σ$ detection of bright giant pulses ($\sim$20 kJy) from Crab-like pulsars if located at the distance of M33. We discuss the implications of our null results for various source populations within the galaxy and comment on the future prospects to conduct even more sensitive searches with the upcoming next-generation instruments including the Square Kilometer Array and its pathfinders.

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arXiv2011

RRATs: New Discoveries, Timing Solutions & Musings

We describe observations of Rotating RAdio Transients (RRATs) that were discovered in a re-analysis of the Parkes Multi-beam Pulsar Survey (PMPS). The sources have now been monitored for sufficiently long to obtain seven new coherent timing solutions, to make a total of 14 now known. Furthermore we announce the discovery of 7 new transient sources, one of which may be extragalactic in origin (with $z\sim0.1$) and would then be a second example of the so-called `Lorimer burst'. The timing solutions allow us to infer neutron star characteristics such as energy-loss rate, magnetic field strength and evolutionary timescales, as well as facilitating multi-wavelength followup by providing accurate astrometry. All of this enables us to consider the question of whether or not RRATs are in any way special, i.e. a distinct and separate population of neutron stars, as has been previously suggested. We see no reason to consider 'RRAT' as anything other than a detection label, the subject of a selection effect in the parameter space searched. However, single-pulse searches can be utilised to great effect to identify pulsars difficult, or impossible, to find by other means, in particular those with long-periods (half of the PMPS RRATs have periods greater than 4 seconds), high-magnetic field strengths ($B\gtrsim 10^{13}$ G) and pulsars approaching the 'death valley'. The detailed nulling properties of such pulsars are unknown but the mounting evidence suggests a broad range of behaviour in the pulsar population. The group of RRATs fit in to the picture where pulsar magnetospheres switch between stable configurations.

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arXiv2011

Arecibo PALFA Survey and Einstein@Home: Binary Pulsar Discovery by Volunteer Computing

We report the discovery of the 20.7 ms binary pulsar J1952+2630, made using the distributed computing project Einstein@Home in Pulsar ALFA survey observations with the Arecibo telescope. Follow-up observations with the Arecibo telescope confirm the binary nature of the system. We obtain a circular orbital solution with an orbital period of 9.4 hr, a projected orbital radius of 2.8 lt-s, and a mass function of f = 0.15 solar masses by analysis of spin period measurements. No evidence of orbital eccentricity is apparent; we set a 2-sigma upper limit e < 1.7e-3. The orbital parameters suggest a massive white dwarf companion with a minimum mass of 0.95 solar masses, assuming a pulsar mass of 1.4 solar masses. Most likely, this pulsar belongs to the rare class of intermediate mass binary pulsars. Future timing observations will aim to determine the parameters of this system further, measure relativistic effects, and elucidate the nature of the companion star.

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arXiv2011

Pulsar Science with the Green Bank 43m Telescope

The 43m telescope at the NRAO site in Green Bank, WV has recently been outfitted with a clone of the Green Bank Ultimate Pulsar Processing Instrument (GUPPI \cite{Ransom:2009}) backend, making it very useful for a number of pulsar related studies in frequency ranges 800-1600 MHz and 220-440 MHz. Some of the recent science being done with it include: monitoring of the Crab pulsar, a blind search for transient sources, pulsar searches of targets of opportunity, and an all-sky mapping project. For the Crab monitoring project, regular observations are searched for giant pulses (GPs), which are then correlated with $γ$-ray photons from the \emph{Fermi} spacecraft. Data from the all-sky mapping project are first run through a pipeline that does a blind transient search, looking for single pulses over a DM range of 0-500 pc~cm$^{-3}$. These projects are made possible by MIT Lincoln Labs.

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arXiv2011

Correlation of Fermi photons with high-frequency radio giant pulses from the Crab pulsar

To constrain the giant pulse (GP) emission mechanism and test the model of Lyutikov (2007) for GP emission, we have carried out a campaign of simultaneous observations of the Crab pulsar at gamma-ray (Fermi) and radio (Green Bank Telescope) wavelengths. Over 10 hours of simultaneous observations we obtained a sample of 2.1x10^4 giant pulses, observed at a radio frequency of 9 GHz, and 77 Fermi photons, with energies between 100 MeV and 5 GeV. The majority of GPs came from the interpulse (IP) phase window. We found no change in the GP generation rate within 10-120 s windows at lags of up to +-40 min of observed gamma-ray photons. The 95% upper limit for a gamma-ray flux enhancement in pulsed emission phase window around all GPs is 4 times the average pulsed gamma-ray flux from the Crab. For the subset of IP GPs, the enhancement upper limit, within the IP emission window, is 12 times the average pulsed gamma-ray flux. These results suggest that GPs, at least high-frequency IP GPs, are due to changes in coherence of radio emission rather than an overall increase in the magnetospheric particle density.

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arXiv2010

On the nature and evolution of the unique binary pulsar J1903+0327

(abridged) PSR J1903+0327, a millisecond pulsar in an eccentric (e = 0.44) 95-day orbit with a (~ 1Msun) companion poses a challenge to our understanding of stellar evolution in binary and multiple-star systems. Here we describe optical and radio observations which rule out most of the scenarios proposed to explain formation of this system. Radio timing measurements of three post-Keplerian effects yield the most precise measurement of the mass of a millisecond pulsar to date: 1.667 +/- 0.021 solar masses (99.7% confidence limit) (...). Optical spectroscopy of a proposed main sequence counterpart show that its orbital motion mirrors the pulsar's 95-day orbit; being therefore its binary companion (...) The optical detection also provides a measurement of the systemic radial velocity of the binary; this and the proper motion measured from pulsar timing allow the determination of the systemic 3-D velocity in the Galaxy. We find that the system is always within 270 pc of the plane of the Galaxy, but always more than 3 kpc away from the Galactic centre. Thus an exchange interaction in a dense stellar environment (like a globular cluster or the Galactic centre) is not likely to be the origin of this system. We suggest that after the supernova that formed it, the neutron star was in a tight orbit with a main-sequence star, the present companion was a tertiary farther out. The neutron star then accreted matter from its evolving inner MS companion, forming a millisecond pulsar. The former donor star then disappears, either due to a chaotic 3-body interaction with the outer star (caused by the expansion of the inner orbit that necessarily results from mass transfer), or in the case of a very compact inner system, due to ablation/accretion by the newly formed millisecond pulsar.

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arXiv2010

A 6.5-GHz Multibeam Pulsar Survey

A survey of the Galactic plane in the region $-60\degree \leq l \leq 30\degree$, $|b| \leq 0.25\degree$ was carried out using the seven-beam Parkes Methanol Multibeam (MMB) receiver, which operates at a frequency of 6.5 GHz. Three pulsars were discovered, and 16 previously known pulsars detected. In this paper we present two previously-unpublished discoveries, both with extremely high dispersion measures, one of which is very close, in angular distance, to the Galactic centre. The survey data also contain the first known detection, at radio frequencies, of the radio magnetar PSR J1550-5418. Our survey observation was made 46 days prior to that previously published and places constraints on the beginning of pulsed radio emission from the source. The detection of only three previously undiscovered pulsars argues that there are few pulsars in the direction of the inner Galaxy whose flux density spectrum is governed by a flat power law. However, these pulsars would be likely to remain undetected at lower frequencies due to the large amount of scatter broadening which affects pulsars with high values of dispersion measure. Surveys with future telescopes at high observing frequencies will, therefore, play an important role in the discovery of pulsars at the Galactic centre. By simulating pulsar surveys of the Galaxy with Phase 1 SKA at frequencies of 1.4 GHz and 10 GHz, we find that high-frequency observations are the only way to discover and observe the Galactic-centre pulsar population.

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