arXiv subjects

M. A. McLaughlin

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

At least 217 records · Page 12Linked to original sources

arXiv2004

X-Ray Emission from the Double Pulsar System J0737-3039

We report on a 10 ksec observation of the double pulsar system J0737-3039 obtained with the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer. We detect the system as a point source with coordinates (J2000) RA = 07:37:51.23, Decl. = -30:39:40.9, making this the first double neutron star system to be detected at X-ray energies. Only 77 source counts are detected. The data are represented satisfactorily by a power-law spectrum with photon index = 2.9 +/- 0.4. The inferred 0.2-10 keV luminosity is approximately 2e30 erg/s for a distance of 0.5 kpc. We do not detect any significant variability with orbital phase in these data, which span one full orbit. These results are consistent with the X-ray emission originating solely from the magnetosphere of the energetic A pulsar, with an efficiency for conversion of rotational energy to X-rays in this band of roughly 0.04%, although we cannot exclude other possibilities.

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arXiv2004

A Double-Pulsar System - A Rare Laboratory for Relativistic Gravity and Plasma Physics

The clock-like properties of pulsars moving in the gravitational fields of their unseen neutron-star companions have allowed unique tests of general relativity and provided evidence for gravitational radiation. We report here the detection of the 2.8-sec pulsar J0737-3039B as the companion to the 23-ms pulsar J0737-3039A in a highly-relativistic double-neutron-star system, allowing unprecedented tests of fundamental gravitational physics. We observe a short eclipse of J0737-3039A by J0737-3039B and orbital modulation of the flux density and pulse shape of J0737-3039B, probably due to the influence of J0737-3039A's energy flux upon its magnetosphere. These effects will allow us to probe magneto-ionic properties of a pulsar magnetosphere.

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arXiv2003

An increased estimate of the merger rate of double neutron stars from observations of a highly relativistic system

The merger of close binary systems containing two neutron stars should produce a burst of gravitational waves, as predicted by the theory of general relativity. A reliable estimate of the double-neutron-star merger rate in the Galaxy is crucial in order to predict whether current gravity wave detectors will be successful in detecting such bursts. Present estimates of this rate are rather low, because we know of only a few double-neutron-star binaries with merger times less than the age of the Universe. Here we report the discovery of a 22-ms pulsar, PSR J0737-3039, which is a member of a highly relativistic double-neutron-star binary with an orbital period of 2.4 hours. This system will merge in about 85 Myr, a time much shorter than for any other known neutron-star binary. Together with the relatively low radio luminosity of PSR J0737-3039, this timescale implies an order-of-magnitude increase in the predicted merger rate for double-neutron-star systems in our Galaxy (and in the rest of the Universe).

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arXiv2003

'Notches' in the Profiles of Bright Pulsars

We discuss the discovery of `notch-like' features in the mean pulse profile of the nearby, bright pulsar B0950+08. We compare these low-level features with those previously seen in the pulse profiles of pulsars J0437-4715 and B1929+10. While J0437-4715 is a binary millisecond pulsar and B0950+08 and B1929+10 are isolated, slow pulsars, all three pulsars are nearby and very bright. Furthermore, all three have detectable emission over an unusually wide range of pulse phase. We describe the similar properties of the notch features seen in all three pulsars and discuss possible interpretations.

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arXiv2003

PSR J0609+2130: A disrupted binary pulsar?

We report the discovery and initial timing observations of a 55.7-ms pulsar, J0609+2130, found during a 430-MHz drift-scan survey with the Arecibo radio telescope. With a spin-down rate of $3.1 \times 10^{-19}$ s s$^{-1}$ and an inferred surface dipole magnetic field of only $4.2 \times 10^{9}$ G, J0609+2130 has very similar spin parameters to the isolated pulsar J2235+1506 found by Camilo, Nice & Taylor (1993). While the origin of these weakly magnetized isolated neutron stars is not fully understood, one intriguing possibility is that they are the remains of high-mass X-ray binary systems which were disrupted by the supernova explosion of the secondary star.

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arXiv2003

Gamma-Ray Pulsars: Modeling and Searches

Using a likelihood analysis (updated since McLaughlin & Cordes 2000) and EGRET detections, upper limits and diffuse background measurements, we find a best-fit luminosity law for the gamma-ray pulsar population. We find that roughly 30 of the 170 unidentified EGRET sources are likely to be pulsars. This is roughly twice the number of known radio pulsars which are plausibly associated with unidentified EGRET sources. We predict that AGILE will detect roughly 70 pulsars as point sources, including 12 which will be able to be detected in blind periodicity searches. GLAST should detect roughly 1200 pulsars (including only 200 currently known radio pulsars), 210 of which will be able to be detected in blind searches. We discuss methods of searching for pulsars in gamma-ray data and present results from our searches for gamma-ray periodicities from new radio pulsars associated with unidentified EGRET sources.

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arXiv2003

New Pulsars Discovered in Arecibo Drift-Scan Searches

We report on new pulsars discovered in Arecibo drift-scan data. Processing of 2200 square degrees of data has resulted in the detection of 41 known and 12 new pulsars. New pulsars include two millisecond pulsars, one solitary and one binary recycled pulsar, and one pulsar with very unusual pulse profile morphology and complex drifting subpulse behavior.

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arXiv2003

Two Radio Pulsars with Magnetar Fields

PSRs J1847-0130 and J1718-37184 have inferred surface dipole magnetic fields greater than those of any other known pulsars and well above the ``quantum critical field'' above which some models predict radio emission should not occur.These fields are similar to those of the anomalous X-ray pulsars (AXPs), which growing evidence suggests are ``magnetars''. The lack of AXP-like X-ray emission from these radio pulsars (and the non-detection of radio emission from the AXPs) creates new challenges for understanding pulsar emission physics and the relationship between these classes of apparently young neutron stars.

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arXiv2003

Searches for Fast Radio Transients

We discuss optimal detection of fast radio transients from astrophysical objects while taking into account the effects of propagation through intervening ionized media, including dispersion, scattering and scintillation.Our analysis applies to the giant-pulse phenomenon exhibited by some pulsars, for which we show examples, and to radio pulses from other astrophysical sources, such as prompt radio emission from gamma-ray burst sources and modulated signals from extra-terrestrial civilizations.

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arXiv2003

Searches for Giant Pulses from Extragalactic Pulsars

We discuss the giant-pulse phenomenon exhibited by pulsars and the distances to which giant pulses might be detected from extragalactic pulsars. We describe the conditions under which a single-pulse search is more sensitive than a standard periodicity search. We find that, for certain pulse-amplitude distribution power laws and time series lengths, single-pulse searches can be superior. We present the results of searches toward several extragalactic targets, including M33, the LMC (PSR B0540-69) and several other galaxies. While we have not conclusively detected giant pulses from any of these targets, these searches illustrate the methodology of, issues related to and difficulties in these types of searches.

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arXiv2003

PSR J1847-0130: A Radio Pulsar with Magnetar Spin Characteristics

We report the discovery of PSR J1847-0130, a radio pulsar with a 6.7-s spin period, in the Parkes multibeam survey of the Galactic plane. The slowdown rate for the pulsar, 1.3x10^{-12} s/s, is high and implies a surface dipole magnetic field strength of 9.4x10^{13} G. This inferred dipolar magnetic field strength is the highest by far among all known radio pulsars and over twice the ``quantum critical field'' above which some models predict radio emission should not occur. The inferred dipolar magnetic field strength and period of this pulsar are in the same range as those of the anomalous X-ray pulsars, which have been identified as being "magnetars" whose luminous X-ray emission is powered by their large magnetic fields. We have examined archival ASCA data and place an upper limit on the X-ray luminosity of J1847-0130 which is lower than the luminosities of all but one AXP. The properties of this pulsar prove that inferred dipolar magnetic field strength and period cannot alone be responsible for the unusual high-energy properties of the magnetars and creates new challenges for understanding the possible relationship between these two manifestations of young neutron stars.

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arXiv2003

The Brightest Pulses in the Universe: Multifrequency Observations of the Crab Pulsar's Giant Pulses

We analyze the Crab pulsar at ten frequencies from 0.43 to 8.8 GHz using data obtained at the Arecibo Observatory. Giant pulses occur only in the main and interpulse components manifest from radio frequencies to gamma-ray energies. Individual giant pulses reach brightness temperatures of at least $10^{32}$K in our data, which do not resolve the narrowest pulses, and are known to reach $10^{37}$K in nanosecond-resolution observations (Hankins et al 2003). Giant pulses are therefore the brightest known in the observable universe and represent an important milestone for theories of the pulsar emission mechanism to explain. Their short durations allow them to serve as especially sensitive probes of the Crab Nebula and the interstellar medium. We analyze frequency structure in individual giant pulses using a scintillating, amplitude-modulated,polarized shot-noise model. The frequency structure associated with multipath propagation decorrelates on a time scale of 25 sec at 1.5 GHz, which requires that multipath propagation be strongly influenced by material within the Crab Nebula. Additional frequency structure decorrelates faster than one spin period, as would be expected from the shot-noise pattern of nanosecond duration pulses emitted by the pulsar. Taking into account the Crab pulsar's locality inside a bright supernova remnant, we conclude that the brightest pulse in a typical 1-hour observation would be most easily detectable in our lowest frequency band (0.43 GHz) to a distance of 1.6 Mpc. We also discuss the detection of such pulses using future instruments such as LOFAR and the SKA.

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arXiv2003

The Parkes multibeam pulsar survey: III. Young pulsars & the discovery and timing of 200 pulsars

The Parkes multibeam pulsar survey has unlocked vast areas of the Galactic plane which were previously invisible to earlier low-frequency and less-sensitive surveys. The survey has discovered more than 600 new pulsars so far, including many that are young and exotic. In this paper we report the discovery of 200 pulsars for which we present positional and spin-down parameters, dispersion measures, flux densities and pulse profiles. A large number of these new pulsars are young and energetic, and we review possible associations of $γ$-ray sources with the sample of about 1300 pulsars for which timing solutions are known. Based on a statistical analysis, we estimate that about $19\pm6$ associations are genuine. The survey has also discovered 12 pulsars with spin properties similar to those of the Vela pulsar, nearly doubling the known population of such neutron stars. Studying the properties of all known `Vela-like' pulsars, we find their radio luminosities to be similar to normal pulsars, implying that they are very inefficient radio sources. Finally, we review the use of the newly discovered pulsars as Galactic probes and discuss the implications of the new NE2001 Galactic electron density model for the determination of pulsar distances and luminosities.

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arXiv2003

Yet MORE PM Survey Discoveries....?

The Parkes Multibeam (PM) survey has found nearly 50% of the >1400 known pulsars and detected 20% of the pulsars in binary systems (75% within the survey area), few of these are millisecond pulsars with orbits of less than one day. It is known that the normal search techniques used in the PM Survey have selected against finding binary pulsars, due to the long integration times used. The relative performance of the search techniques used and the improvements made prior to the complete reprocessing of the data currently being undertaken are discussed. The processing is being done on COBRA - the new supercomputer at Jodrell Bank. The results of the reprocessing, as well as adding more solitary pulsars, will give more confidence on the population and types of binaries in the Galactic plane. However, it can be shown that for millisecond pulsars in binary orbits of between 20min and a few hours, the search techniques are still relatively insensitive.

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arXiv2002

New Pulsars from Arecibo Drift-Scan Searches

We report new pulsars discovered in drift-scan data taken by two collaborations (Berkeley/Cornell and STScI/NAIC) during the latter stages of the Arecibo upgrade period. The data were taken with the Penn State Pulsar Machine and are being processed on the COBRA cluster at Jodrell Bank. Processing is roughly 70% complete and has resulted in the detection of 10 new and 31 known pulsars, in addition to a number of pulsar candidates. The 10 new pulsars include one pulsar with a spin-period of 55 ms and another with a spin period of 5.8 ms. At the completion of the processing, we expect to have discovered roughly 20 new pulsars. All new pulsars are being subjected to a program of followup observations at Arecibo to determine spin and astrometric parameters.

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arXiv2002

Discovery of radio pulsations from the X-ray pulsar J0205+6449 in supernova remnant 3C58 with the Green Bank Telescope

We report the discovery with the 100 m Green Bank Telescope of 65 ms radio pulsations from the X-ray pulsar J0205+6449 at the center of supernova remnant 3C58, making this possibly the youngest radio pulsar known. From our observations at frequencies of 820 and 1375 MHz, the free electron column density to PSR J0205+6449 is found to be 140.7 +- 0.3 pc/cc. The barycentric pulsar period P and period derivative determined from a phase-coherent timing solution are consistent with the values previously measured from X-ray observations. The averaged radio profile of PSR J0205+6449 consists of one sharp pulse of width ~ 3 ms ~ 0.05 P. The pulsar is an exceedingly weak radio source, with pulse-averaged flux density in the 1400 MHz band of 0.045 mJy and a spectral index of ~ -2.1. Its radio luminosity of ~ 0.5 mJy kpc^2 at 1400 MHz is lower than that of ~ 99% of known pulsars and is the lowest among known young pulsars.

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arXiv2001

PSR J1740+1000: A Young Pulsar Well Out Of The Galactic Plane

We discuss PSR J1740+1000, one of five pulsars recently discovered in a search of 470 square degrees at 430 MHz during the upgrade of the 305-m Arecibo telescope. The period of 154 ms and period derivative of 2.1 x 10^-14 s/s imply a spin-down age of 114 kyr that is smaller than 95% of all known pulsars. The youth and proximity of this pulsar make it a good candidate for detection at X-ray and gamma-ray energies. Its high Galactic latitude of 20.4 degrees suggests a very high velocity if the pulsar was born in the midplane of the Galaxy and if its kinematic age equals its spindown age. Interstellar scintillations, however, suggest a much lower velocity. We discuss possible explanations for this discrepancy, taking into account (a) possible birth sites away from the midplane; (b) contributions from the unmeasured radial velocity; (c) a kinematic age different from the spin-down age; and (d) biasing of the scintillation velocity by enhanced scattering from the North Polar Spur.

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arXiv2001

Upper Limits On Periodic, Pulsed Radio Emission from the X-Ray Point Source in Cassiopeia A

The Chandra X-ray Observatory recently discovered an X-ray point source near the center of Cassiopeia A, the youngest known Galactic supernova remnant. We have conducted a sensitive search for radio pulsations from this source with the Very Large Array, taking advantage of the high angular resolution of the array to resolve out the emission from the remnant itself. No convincing signatures of a dispersed, periodic source or of isolated dispersed pulses were found, whether for an isolated or a binary source. We derive upper limits of 30 and 1.3 mJy at 327 and 1435 MHz for the phase-averaged pulsed flux density from this source. The corresponding luminosity limits are lower than those for any pulsar with age less than 10^4 years. The sensitivities of our search to single pulses were 25 and 1.0 Jy at 327 and 1435 MHz. For comparison, the Crab pulsar emits roughly 80 pulses per minute with flux densities greater than 100 Jy at 327 MHz and 8 pulses per minute with flux densities greater than 50 Jy at 1435 MHz. These limits are consistent with the suggestion that the X-ray point source in Cas A adds to the growing number of neutron stars which are not radio pulsars.

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