arXiv subjects

A. G. Lyne

Publications and source records attributed to A. G. Lyne.

At least 163 records · Page 9Linked to original sources

arXiv2008

Pulsar Timing for the Fermi Gamma-ray Space Telescope

We describe a comprehensive pulsar monitoring campaign for the Large Area Telescope (LAT) on the {\em Fermi Gamma-ray Space Telescope} (formerly GLAST). The detection and study of pulsars in gamma rays give insights into the populations of neutron stars and supernova rates in the Galaxy, into particle acceleration mechanisms in neutron star magnetospheres, and into the "engines" driving pulsar wind nebulae. LAT's unprecedented sensitivity between 20 MeV and 300 GeV together with its 2.4 sr field-of-view makes detection of many gamma-ray pulsars likely, justifying the monitoring of over two hundred pulsars with large spin-down powers. To search for gamma-ray pulsations from most of these pulsars requires a set of phase-connected timing solutions spanning a year or more to properly align the sparse photon arrival times. We describe the choice of pulsars and the instruments involved in the campaign. Attention is paid to verifications of the LAT pulsar software, using for example giant radio pulses from the Crab and from PSR B1937+21 recorded at Nançay, and using X-ray data on PSR J0218+4232 from XMM-Newton. We demonstrate accuracy of the pulsar phase calculations at the microsecond level. Data Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ .

astro-ph↗

arXiv2008

Simultaneous multi-frequency single-pulse properties of AXP XTE J1810-197

We have used the 76-m Lovell, 94-m equivalent WSRT and 100-m Effelsberg radio telescopes to investigate the simultaneous single-pulse properties of the radio emitting magnetar AXP XTE J1810-197 at frequencies of 1.4, 4.8 and 8.35 GHz during May and July 2006. We study the magnetar's pulse-energy distributions which are found to be very peculiar as they are changing on time-scales of days and cannot be fit by a single statistical model. The magnetar exhibits strong spiky single giant-pulse-like subpulses, but they do not fit the definition of the giant pulse or giant micropulse phenomena. Measurements of the longitude-resolved modulation index reveal a high degree of intensity fluctuations on day-to-day time-scales and dramatic changes across pulse phase. We find the frequency evolution of the modulation index values differs significantly from what is observed in normal radio pulsars. We find that no regular drifting subpulse phenomenon is present at any of the observed frequencies at any observing epoch. However, we find a quasi-periodicity of the subpulses present in the majority of the observing sessions. A correlation analysis indicates a relationship between components from different frequencies. We discuss the results of our analysis in light of the emission properties of normal radio pulsars and a recently proposed model which takes radio emission from magnetars into consideration.

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arXiv2008

PSR J1753-2240: A mildly recycled pulsar in an eccentric binary system

We report the discovery of PSR J1753-2240 in the Parkes Multibeam Pulsar Survey database. This 95-ms pulsar is in an eccentric binary system with a 13.6-day orbital period. Period derivative measurements imply a characteristic age in excess of 1 Gyr, suggesting that the pulsar has undergone an episode of accretion-induced spin-up. The eccentricity and spin period are indicative of the companion being a second neutron star, so that the system is similar to that of PSR J1811-1736, although other companion types cannot be ruled out at this time. The companion mass is constrained by geometry to lie above 0.48 solar masses, although long-term timing observations will give additional constraints. If the companion is a white dwarf or main sequence star, optical observations may yield a direct detection of the companion. If the system is indeed one of the few known double neutron star systems, it would lie significantly far from the recently proposed spin-period/eccentricity relationship.

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arXiv2008

Radio spectrum of the AXP J1810-197 and of its profile components

As part of a European Pulsar Network (EPN) multi-telescope observing campaign, we performed simultaneous multi-frequency observations at 1.4, 4.9 and 8.4 GHz during July 2006 and quasi-simultaneous multi-frequency observations from Decem- ber 2006 until July 2007 at 2.7, 4.9, 8.4, 14.6 and 32 GHz, in order to obtain flux density measurements and spectral features of the 5.5-sec radio-emitting magnetar AXP J1810-197. We monitored the spectral evolution of its pulse shape which consists of a main pulse (MP) and an interpulse (IP). We present the flux density spectrum of the average profile and of the separate pulse components of this first-known radio-emitting transient anomalous X-ray pulsar. We observe a decrease of the flux density by a factor of 10 within 8 months and follow the disappearance of one of the two main components. Although the spectrum is generally flat, we observe large fluctuations of the spectral index with time. For that reason we have made some measurements of modulation indices for individual pulses in order to also investigate the origin of these fluctuations.

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arXiv2008

PSR J1856+0245: Arecibo Discovery of a Young, Energetic Pulsar Coincident with the TeV Gamma-ray Source HESS J1857+026

We present the discovery of the Vela-like radio pulsar J1856+0245 in the Arecibo PALFA survey. PSR J1856+0245 has a spin period of 81ms, a characteristic age of 21kyr, and a spin-down luminosity Edot = 4.6 x 10^36 ergs/s. It is positionally coincident with the TeV gamma-ray source HESS J1857+026, which has no other known counterparts. Young, energetic pulsars create wind nebulae, and more than a dozen pulsar wind nebulae have been associated with very-high-energy (100GeV-100TeV) gamma-ray sources discovered with the HESS telescope. The gamma-ray emission seen from HESS J1857+026 is potentially produced by a pulsar wind nebula powered by PSR J1856+0245; faint X-ray emission detected by ASCA at the pulsar's position supports this hypothesis. The inferred gamma-ray efficiency is epsilon_gamma = L_gamma/Edot = 3.1% (1-10TeV, for a distance of 9kpc), comparable to that observed in similar associations.

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arXiv2008

PSR J1410-6132: A young, energetic pulsar associated with EGRET source 3EG J1410-6147

We present the discovery of PSR J1410-6132, a 50-ms pulsar found during a high-frequency survey of the Galactic plane, using a 7-beam 6.3-GHz receiver on the 64-m Parkes radio telescope. The pulsar lies within the error box of the unidentified EGRET source 3EG J1410-6147, has a characteristic age of 26 kyr and a spin-down energy of 10^37 erg s^-1. It has a very high dispersion measure of 960+/-10 cm^-3 pc and the largest rotation measure of any pulsar, RM=+2400 +/- 30 rad m^-2. The pulsar is very scatter-broadened at frequencies of 1.4 GHz and below, making pulsed emission almost impossible to detect. Assuming a distance of 15 kpc, the pulsar's spin-down energy and a gamma-ray efficiency factor of ~10 per cent is sufficient to power the gamma-ray source. We therefore believe we have identified the nature of 3EG J1410-6147. This new discovery suggests that deep targeted high-frequency surveys of inner-galaxy EGRET sources could uncover further young, energetic pulsars.

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arXiv2008

The very soft X-ray spectrum of the Double Pulsar System J0737-3039

We present the results of an 80 ks Chandra ACIS-S observation of the double pulsar system J0737-3039. Furthermore, we report on spectral, spatial and timing analysis of the combined X-ray observations performed so far for this system. Fitting a total of ~1100 photons, we show that the X-ray spectrum of the J0737-3039 system is very soft, and not satisfactorily modeled by a simple blackbody or an atmospheric model. However, it is not possible yet to discriminate between a predominantly non-thermal and a predominantly thermal origin for the X-ray emission. Adopting a simple power-law emission model, the photon index (Gamma=3.7) and the implied conversion efficiency of the rotational energy of PSR J0737-3039A into X-ray emission (4.1x10^-4, for a distance to the source of 500 pc) are compatible with the X-ray photons being emitted in the magnetosphere of PSR J0737-3039A. This hypothesis is also supported by the absence of detectable X-ray orbital modulation (up to ~20%) or any X-ray nebular emission and it is in agreement with the high (~75%) X-ray pulsed fraction of PSR J0737-3039A. A two blackbody or a Comptonized blackbody model also reproduce the data, and the upper limit to the value of the hydrogen column density N_H <10^20 cm^-2, is in better agreement (with respect to the power-law model) with the Galactic N_H in that direction and at that distance. For the two blackbody model the implied emission radii and temperatures are also compatible with those seen in other recycled pulsars, calling for the bulk of the X-ray photons being originated from heated regions at the surface of pulsar A. On the other hand, in the Comptonized blackbody model, the electron temperature seems to be significantly smaller than in other similar objects.

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arXiv2007

The double pulsar: evolutionary constraints from the system geometry

The double pulsar system PSR J0737-3039A/B is a highly relativistic double neutron star (DNS) binary, with a 2.4-hour orbital period. The low mass of the second-formed NS, as well the low system eccentricity and proper motion, point to a different evolutionary scenario compared to other known DNS systems. We describe analysis of the pulse profile shape over 6 years of observations, and present the resulting constraints on the system geometry. We find the recycled pulsar in this system, PSR J0737-3039A, to have a low misalignment between its spin and orbital angular momentum axes, with a 68.3% upper limit of 6.1 degrees, assuming emission from both magnetic poles. This tight constraint lends credence to the idea that the supernova that formed the second pulsar was relatively symmetric, possibly involving electron-capture onto an O-Ne-Mg core.

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arXiv2007

A 610-MHz Galactic Plane Pulsar Search with the Giant Meterwave Radio Telescope

We report on the discovery of three new pulsars in the first blind survey of the north Galactic plane (45 < l < 135 ; |b| < 1) with the Giant Meterwave Radio telescope (GMRT) at an intermediate frequency of 610 MHz. The timing parameters, obtained in follow up observations with the Lovell Telescope at Jodrell Bank Observatory and the GMRT, are presented.

astro-ph↗

arXiv2007

Upper limits on gravitational wave emission from 78 radio pulsars

We present upper limits on the gravitational wave emission from 78 radio pulsars based on data from the third and fourth science runs of the LIGO and GEO600 gravitational wave detectors. The data from both runs have been combined coherently to maximise sensitivity. For the first time pulsars within binary (or multiple) systems have been included in the search by taking into account the signal modulation due to their orbits. Our upper limits are therefore the first measured for 56 of these pulsars. For the remaining 22, our results improve on previous upper limits by up to a factor of 10. For example, our tightest upper limit on the gravitational strain is 2.6e-25 for PSRJ1603-7202, and the equatorial ellipticity of PSRJ2124-3358 is less than 10^{-6}. Furthermore, our strain upper limit for the Crab pulsar is only 2.2 times greater than the fiducial spin-down limit.

gr-qc↗

arXiv2007

Discovery of Pulsations and a Possible Spectral Feature in the X-ray Emission from Rotating Radio Transient J1819-1458

PSR J1819-1458 is a rotating radio transient (RRAT) source with an inferred surface dipole magnetic field strength of 5e13 G and a 4.26-s spin period. We present XMM-Newton observations of the X-ray counterpart of this source, CXOU J181939.1-145804, in which we identify pulsations and a possible spectral feature. The X-ray pulsations are at the period predicted by the radio ephemeris, providing an unambiguous identification with the radio source and confirmation of its neutron star nature. The X-ray pulse has a 0.3-5 keV pulsed fraction of 34% and is aligned with the expected phase of the radio pulse. The X-ray spectrum is fit well by an absorbed blackbody with kT = 0.14 keV with the addition of an absorption feature at 1 keV, with total absorbed flux of 1.5e-13 ergs/cm^2/s (0.3-5 keV). This absorption feature is well modeled by a Gaussian or resonant cyclotron scattering model, but its significance is dependent on the choice of continuum model. We find no evidence for any X-ray bursts or aperiodic variability on timescales of 6 ms to the duration of the observation and can place the most stringent limit to date of < 3e-9 ergs/cm^2/s on the absorbed 0.3-5 keV flux of any bursts.

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arXiv2007

Age constraints in the double pulsar system J0737-3039

We investigate the age constraints that can be placed on the double pulsar system using models for the spin-down of the first-born 22.7-ms pulsar A and the 2.77-s pulsar B with characteristic ages of 210 and 50 Myr respectively. Standard models assuming dipolar spin-down of both pulsars suggest that the time since the formation of B is ~50 Myr, i.e. close to B's characteristic age. However, adopting models which account for the impact of A's relativistic wind on B's spin-down we find that the formation of B took place either 80 or 180 Myr ago, depending the interaction mechanism. Formation 80 Myr ago, closer to B's characteristic age, would result in the contribution from J0737-3039 to the inferred coalescence rates for double neutron star binaries increasing by 40%. The 180 Myr age is closer to A's characteristic age and would be consistent with the most recent estimates of the coalescence rate. The new age constraints do not significantly impact recent estimates of the kick velocity, tilt angle between pre and post-supernova orbital planes or pre-supernova mass of B's progenitor.

astro-ph↗

arXiv2007

Polarized radio emission from a magnetar

We present polarization observations of the radio emitting magnetar AXP J1810-197. Using simultaneous multi-frequency observations performed at 1.4, 4.9 and 8.4 GHz, we obtained polarization information for single pulses and the average pulse profile at several epochs. We find that in several respects this magnetar source shows similarities to the emission properties of normal radio pulsars while simultaneously showing striking differences. The emission is nearly 80-95% polarized, often with a low but significant degree of circular polarization at all frequencies which can be much greater in selected single pulses. The position angle swing has a low average slope of only 1 deg/deg, deviating significantly from an S-like swing as often seen in radio pulsars which is usually interpreted in terms of a rotating vector model and a dipolar magnetic field. The observed position angle is consistent at all frequencies while showing significant secular variations. On average the interpulse is less linearly polarized but shows a higher degree of circular polarization. Some epochs reveal the existence of non-orthogonal emission modes in the main pulse and systematic wiggles in the PA swing, while the interpulse shows a large variety of position angle values. We interprete many of the emission properties as propagation effects in a non-dipolar magnetic field configuration where emission from different multipole components is observed.

astro-ph↗

arXiv2006

The binary pulsar PSR J1811-1736: evidence of a low amplitude supernova kick

Aims: The binary pulsar PSR J1811-1736 has been identified, since its discovery, as a member of a double neutron star system. Observations of such binary pulsars allow the measurement of general relativistic effects, which in turn lead to information about the orbiting objects and, in a few cases, to tests of theories of gravity. Methods: Regular timing observations have been carried out with three of the largest European radio telescopes involved in pulsar research. The prospects of continued observations were studied with simulated timing data. Pulse scattering times were measured using dedicated observations at 1.4 GHz and at 3.1 GHz, and the corresponding spectral index has also been determined. The possibility of detecting the yet unseen companion as a radio pulsar was also investigated. A study of the natal kick received by the younger neutron star at birth was performed. Results: We present an up to date and improved timing solution for the binary pulsar PSR J1811-1736. One post-Keplerian parameter, the relativistic periastron advance, is measured and leads to the determination of the total mass of this binary system. The pulse profile at 1.4 GHz is heavily broadened by interstellar scattering, limiting the timing precision achievable at this frequency and the measurability of other post-keplerian parameters. Interstellar scattering is unlikely to be the reason for the continued failure to detect radio pulsations from the companion of PSR J1811-1736. The probability distribution that we derive for the amplitude of the kick imparted on the companion neutron star at its birth indicates that the kick has been of low amplitude.

astro-ph↗

arXiv2006

Simultaneous Single-Pulse Observations of Radio Pulsars: V. On the Broadband Nature of The Pulse Nulling Phenomenon in PSR B1133+16

We revisit the phenomenon of pulse nulling using high-quality single-pulse data of PSR B1133+16 from simultaneous multifrequency observations. Observations were made at 325, 610, 1400 and 4850 MHz as part of a joint program between the European Pulsar Network and the Giant Metrewave Radio Telescope. The pulse energy time series are analysed to derive improved statistics of nulling pulses as well as to investigate the frequency dependence of the phenomenon. The pulsar is observed to be in null state for approximately 15% of the time; however, we find that nulling does not always occur simultaneously at all four frequencies of observation. We characterise this "selective nulling'' as a function of frequency, separation in frequency, and combination of frequencies. The most remarkable case is a significantly large number of nulls ($\approx$6%) at lower frequencies, that are marked by the presence of a fairly narrow emission feature at the highest frequency of 4850 MHz. We refer to these as "low frequency (LF) nulls." Our analysis shows that this high frequency emission tends to occur preferentially over a narrow range in longitude and with pulse widths typically of the order of a few milliseconds. We discuss the implications of our results for the pulsar emission mechanism in general and for the broadbandness of nulling phenomenon in particular. Our results signify the presence of an additional process of emission which does not turn off when the pulsar nulls at low frequencies, and becomes more prominent at higher frequencies. Our analysis also hints at a possible outer gap origin for this new population of pulses, and thus a likely connection to some high-energy emission processes that occur in the outer parts of the pulsar magnetosphere.

astro-ph↗

arXiv2006

Tests of general relativity from timing the double pulsar

The double pulsar system, PSR J0737-3039A/B, is unique in that both neutron stars are detectable as radio pulsars. This, combined with significantly higher mean orbital velocities and accelerations when compared to other binary pulsars, suggested that the system would become the best available testbed for general relativity and alternative theories of gravity in the strong-field regime. Here we report on precision timing observations taken over the 2.5 years since its discovery and present four independent strong-field tests of general relativity. Use of the theory-independent mass ratio of the two stars makes these tests uniquely different from earlier studies. By measuring relativistic corrections to the Keplerian description of the orbital motion, we find that the ``post-Keplerian'' parameter s agrees with the value predicted by Einstein's theory of general relativity within an uncertainty of 0.05%, the most precise test yet obtained. We also show that the transverse velocity of the system's center of mass is extremely small. Combined with the system's location near the Sun, this result suggests that future tests of gravitational theories with the double pulsar will supersede the best current Solar-system tests. It also implies that the second-born pulsar may have formed differently to the usually assumed core-collapse of a helium star.

astro-ph↗

arXiv2006

Timing of millisecond pulsars in NGC 6752 - II. Proper motions of the pulsars in the cluster outskirts

Exploiting a five-year span of data, we present improved timing solutions for the five millisecond pulsars known in the globular cluster NGC 6752. They include proper motion determinations for the two outermost pulsars in the cluster, PSR J1910-5959A and PSR J1910-5959C. The values of the proper motions are in agreement with each other within current uncertainties, but do not match (at 4 sigma and 2 sigma level respectively) with the value of the proper motion of the entire globular cluster derived in the optical band. Implications of these results for the cluster membership of the two pulsars are investigated. Prospects for the detection of the Shapiro delay in the binary system J1910-5959A are also discussed.

astro-ph↗

arXiv2006

The Parkes multibeam pulsar survey: VI. Discovery and timing of 142 pulsars and a Galactic population analysis

[ABRIDGED] We present the discovery and follow-up observations of 142 pulsars found in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. These new discoveries bring the total number of pulsars found by the survey to 742. In addition to tabulating spin and astrometric parameters, along with pulse width and flux density information, we present orbital characteristics for 13 binary pulsars which form part of the new sample. Combining these results from another recent Parkes multibeam survey at high Galactic latitudes, we have a sample of 1008 normal pulsars which we use to carry out a determination of their Galactic distribution and birth rate. We infer a total Galactic population of 30000 +/- 1100 potentially detectable pulsars (i.e. those beaming towards us) having 1.4-GHz luminosities above 0.1 mJy kpc squared. Using a pulsar current analysis, we derive the birth rate of this population to be 1.4 +/- 0.2 pulsars per century. An important conclusion from our work is that the inferred radial density function of pulsars depends strongly on the assumed distribution of free electrons in the Galaxy. As a result, any analyses using the most recent electron model of Cordes & Lazio predict a dearth of pulsars in the inner Galaxy. We show that this model can also bias the inferred pulsar scale height with respect to the Galactic plane. Combining our results with other Parkes multibeam surveys we find that the population is best described by an exponential distribution with a scale height of 330 pc.

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