arXiv subjects

R. N. Manchester

Publications and source records attributed to R. N. Manchester.

At least 181 records · Page 10Linked to original sources

arXiv2005

Testing GR with the Double Pulsar: Recent Results

This first ever double pulsar system consists of two pulsars orbiting the common center of mass in a slightly eccentric orbit of only 2.4-hr duration. The pair of pulsars with pulse periods of 22 ms and 2.8 sec, respectively, confirms the long-proposed recycling theory for millisecond pulsars and provides an exciting opportunity to study the works of pulsar magnetospheres by a very fortunate geometrical alignment of the orbit relative to our line-of-sight. In particular, this binary system represents a truly unique laboratory for relativistic gravitational physics. This contribution serves as an update on the currently obtained results and their consequences for the test of general relativity in the strong-field regime. A complete and more up-to-date report of the timing results will be presented elsewhere shortly.

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arXiv2005

Polarisation profiles of southern pulsars at 3.1 GHz

We present polarisation profiles for 48 southern pulsars observed with the new 10-cm receiver at the Parkes telescope. We have exploited the low system temperature and high bandwidth of the receiver to obtain profiles which have good signal to noise for most of our sample at this relatively high frequency. Although, as expected, a number of profiles are less linearly polarised at 3.1 GHz than at lower frequencies, we identify some pulsars and particular components of profiles in other pulsars which have increased linear polarisation at this frequency. We discuss the dependence of linear polarisation with frequency in the context of a model in which emission consists of the superposition of two, orthogonally polarised modes. We show that a simple model, in which the orthogonal modes have different spectral indices, can explain many of the observed properties of the frequency evolution of both the linear polarisation and the total power, such as the high degree of linear polarisation seen at all frequencies in some high spin-down, young pulsars. Nearly all the position angle profiles show deviations from the rotating vector model; this appears to be a general feature of high-frequency polarisation observations.

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arXiv2005

A Search for Giant Pulses from Millisecond Pulsars

We have searched for microsecond-timescale broadband emission from a sample of eighteen millisecond pulsars. Our study places strong limits on such emission from several millisecond pulsars and shows that it is only present in a small subset of millisecond pulsars. Giant pulses of up to 64 times the mean pulse energy were detected from PSR J1823-3021A in the globular cluster NGC 6624. In contrast to the giant pulses of PSR B1937+21, nearly all of the giant pulses from PSR J1823-3021A were distributed within the trailing half of the main-pulse component of the integrated pulse profile. The fact that no giant pulses were observed on the leading side of the main-pulse component suggests that giant pulses are preferentially emitted closer to the last open field line than ordinary emission. The correlation between giant pulse emissivity and spin-down luminosity in millisecond pulsars suggests that the high period derivative of PSR J1823-3021A is intrinsic and is not just an artifact of its acceleration in the gravitational potential of NGC 6624.

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arXiv2005

Radio Observations of PSR B1259-63 through the 2004 periastron passage

We report here on extensive radio observations of the binary system containing PSR B1259-63 and the Be star SS 2883, made around the time of the 2004 periastron. This is the fourth periastron to have been observed in detail. As in previous observations, changes in the pulsar's dispersion and rotation measures are detected over a period spanning 200 days. We show that the eclipse of the pulsed emission lasts from 16 days prior to periastron to 15 days after periastron and is consistent from one periastron to the next. We demonstrate that the timing solution proposed by Wang et al. (2004) provides a good fit through the 2004 periastron. The light curve of the transient unpulsed radio emission is broadly similar from one periastron to the next. For this periastron, however, the light curve is strongly peaked post-periastron with rather little enhancement prior to periastron, in contrast to the 2000 periastron where the peak flux densities were more equal. These observations remain consistent with the interpretation that the pulsar passes through the dense circumstellar disk of the Be star just before and just after periastron. The observed differences from one periastron to the next can be ascribed to variations in the local disk density and magnetic field structure at the time the pulsar enters the disk.

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arXiv2005

Long-term Scintillation Observations of Five Pulsars at 1540 MHz

From 2001 January to 2002 June, we monitored PSRs B0329+54, B0823+26, B1929+10, B2020+28 and B2021+51 using the Nanshan 25-m radio telescope of Urumqi Observatory to study their diffractive interstellar scintillation (DISS). The average interval between observations was about 9 days and the observation duration ranged between 2 and 6 hours depending on the pulsar. Wide variations in the DISS parameters were observed over the 18-month data span. Despite this, the average scintillation velocities are in excellent agreement with the proper motion velocities. The average two-dimensional autocorrelation function for PSR B0329+54 is well described by a thin-screen Kolmogorov model, at least along the time and frequency axes. Observed modulation indices for the DISS time scale and bandwidth and the pulsar flux density are greater than values predicted for a Kolmogorov spectrum of electron density fluctuations. Correlated variations over times long compared to the nominal refractive scintillation time are observed, suggesting that larger-scale density fluctuations are important. For these pulsars, the scintillation bandwidth as a function of frequency has a power-law index (~3.6) much less than expected for Kolmogorov turbulence (~4.4). Sloping fringes are commonly observed in the dynamic spectra, especially for PSR B0329+54. The detected range of fringe slopes are limited by our observing resolution. Our observations are sensitive to larger-scale fringes and hence smaller refractive angles, corresponding to the central part of the scattering disk.

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arXiv2004

PSR J1756-2251: a new relativistic double neutron star system

We report the discovery during the Parkes Multibeam Pulsar Survey of PSR J1756-2251, a 28.5 ms pulsar in a relativistic binary system. Subsequent timing observations showed the pulsar to have an orbital period of 7.67 hrs and an eccentricity of 0.18. They also revealed a significant advance of periastron, 2.585+/-0.002 deg./yr. Assuming this is entirely due to general relativity implies a total system mass (pulsar plus companion) of 2.574+/-0.003 solar mass. This mass and the significant orbital eccentricity suggest that this is a double neutron star system. Measurement of the gravitational redshift, gamma, and an evaluation of the Shapiro delay shape, s, indicate a low companion mass of <1.25 solar mass. The expected coalescence time due to emission of gravitational waves is only ~1.7 Gyr substantially less than a Hubble time. We note an apparent correlation between spin period and eccentricity for normally evolving double neutron star systems.

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arXiv2004

The Double Pulsar System J0737-3039: Modulation of A by B at eclipse

We have investigated the eclipse of the 23-ms pulsar J0737-3039A by its 2.8-s companion PSR J0737-3039B in the recently discovered double pulsar system using data taken with the Green Bank Telescope at 820 MHz. We find that the pulsed flux density at eclipse is strongly modulated with half the periodicity of the 2.8-s pulsar. The eclipse occurs earlier and is deeper at those rotational phases of B when its magnetic axis is aligned with the line of sight than at phases when its magnetic axis is at right angles to the line of sight. This is consistent with the eclipse of A being due to synchrotron absorption by the shock-heated plasma surrounding B, the asymmetry arising from the higher plasma densities expected in the B magnetosphere's polar cusps.

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arXiv2004

Mode Switching and Subpulse Drifting in PSR B0826-34

We present high-quality observations of PSR B0826-34 at 1374 MHz. The emission from this pulsar exhibits strong bursts of pulses followed by long periods of `null' pulses. When it is strong, the radiation extends through the whole pulse period. We show for the first time that there is weak emission during the `null' phases, which should therefore be considered to be a different mode rather than a null. During this weak mode the profile is similar to that observed in the strong mode at low radio frequency. Using a phase-tracking method, the pattern of drifting subpulses during the strong mode is seen to be coherent across the whole profile. The drift rate is variable and includes positive and negative values. Thirteen subpulse bands have been directly observed, covering the whole longitude range. The subpulses and their spacings ($P_2$) are wider in one half of the profile than those in the other half. This difference, and the variation of observed $P_2$ within the two regions, can be accounted for if the magnetic pole is inclined to the rotation axis by about 0.5 degrees. These two regions appear to represent radiation from outer and inner cones. The intensity modulation of subpulses in all longitude ranges is related to the magnitude of the drift rate.

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arXiv2004

The Double Pulsar System J0737-3039: Modulation of the radio emission from B by radiation from A

We have analyzed single pulses from PSR J0737-3039B, the 2.8-s pulsar in the recently discovered double pulsar system, using data taken with the Green Bank Telescope at 820 and 1400 MHz. We report the detection of features similar to drifting subpulses, detectable over only a fraction of the pulse window, with a fluctuation frequency of 0.196 cycles/period. This is exactly the beat frequency between the periods of the two pulsars. In addition, the drifting features have a separation within a given pulse of 23 ms, equal to the pulse period of A. These features are therefore due to the direct influence of PSR J0737-3039A's 44-Hz electromagnetic radiation on PSR J0737-3039B's magnetosphere. We only detect them over a small range of orbital phases, when the radiation from the recycled pulsar PSR J0737-3039A meets our line of sight to PSR J0737-3039B from the side.

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arXiv2004

The Parkes Multibeam Pulsar Survey: V. Finding binary and millisecond pulsars

The Parkes Multibeam Pulsar Survey is the most successful survey of the Galactic plane ever performed, finding over 600 pulsars in the initial processing. We report on reprocessing of all 40,000 beams with a number of algorithms, including conventional frequency-domain searches and an acceleration search for fast binary pulsars. The very large volume of results coupled with the need to distinguish new candidates from known pulsars and their many harmonics, often with multiple detections from different search algorithms, necessitated the development of a new graphical selection tool tightly linked to a web-based results database. We discuss and demonstrate the benefits of these software systems which are specifically designed for large survey projects. The results of this processing have been encouraging; we have discovered 128 new pulsars including 11 binary and 15 millisecond pulsars, in addition to those previously found in the survey, we have thus far discovered 737 pulsars. In this paper we discuss the discoveries of PSR J1744-3922, a 172 ms mildly recycled pulsar in a 4.6 hr orbit that exhibits nulling behaviour, not previously observed in recycled or binary objects; PSR J1802-2124, an intermediate mass binary pulsar (IMBP) and PSR J1801-1417, a solitary millisecond pulsar.

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arXiv2004

The Cosmic Coalescence Rates for Double Neutron Star Binaries

This manuscript is an updated version of Kalogera et al. (2004) published in ApJ Letters to correct our calculation of the Galactic DNS in-spiral rate. The details of the original erratum submitted to ApJ Letters are given in page 6 of this manuscript. We report on the newly increased event rates due to the recent discovery of the highly relativistic binary pulsar J0737--3039 (Burgay et al. 2003). Using a rigorous statistical method, we present the calculations reported by Burgay et al., which produce a in-spiral rate for Galactic double neutron star (DNS) systems that is higher by a factor of 5-7 compared to estimates made prior to the new discovery. Our method takes into account known pulsar-survey selection effects and biases due to small-number statistics. This rate increase has dramatic implications for gravitational wave detectors. For the initial Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, the most probable detection rates for DNS in-spirals are one event per 10-630 yr; at 95% confidence, we obtain rates up to one per 3 yr. For the advanced LIGO detectors, the most probable rates are 10-500 events per year. These predictions, for the first time, bring the expectations for DNS detections by the initial LIGO detectors to the astrophysically relevant regime. We also use our models to predict that the large-scale Parkes Multibeam pulsar survey with acceleration searches could detect an average of four binary pulsars similar to those known at present.

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arXiv2004

Chandra Detection of a Synchrotron Nebula Around the Vela-like Pulsar J1016-5857

We report on a 19 ks observation of the pulsar J1016-5857 with the Chandra X-ray Observatory. This "Vela-like" pulsar has rotation period 107 ms, characteristic age 21 kyr, and spin-down power 2.6e36 ergs/s. A relatively bright centrally peaked source of radius ~25" around the radio pulsar position has a spectrum that is well fitted by an absorbed power law with photon index 1.32+-0.25. We regard this as a newly identified pulsar wind nebula that we designate PWN G284.0-1.8. We do not detect the pulsar either as a point X-ray source or as a pulsed source in a 55 ks observation with the Rossi X-ray Timing Explorer. The isotropic PWN luminosity is 3e32 ergs/s in the 2-10 keV range, for a distance of 3 kpc that is consistent with the measured neutral hydrogen column density. The unpulsed flux from the pulsar is less than 30% of the measured PWN flux. The brightest component of the PWN, near the pulsar, shows extended emission of size ~2" that may indicate, by analogy with other young pulsars, the wind termination shock. In the Chandra image we also detect a very faint extended structure ~1' by 2' in size that is highly asymmetric about the pulsar position. This structure is a good match in width and position angle to the tip of a "finger" of radio emission that appears to connect to the nearby supernova remnant G284.3-1.8, but we cannot characterize it further with the available data. There is a variable X-ray point source only 1.5 arcmin from the pulsar, which we identify using optical spectroscopy as an accreting binary.

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arXiv2004

The Mouse That Soared: High Resolution X-ray Imaging of the Pulsar-Powered Bow Shock G359.23-0.82

We present an observation with the Chandra X-ray Observatory of the unusual radio source G359.23-0.82 ("the Mouse"), along with updated radio timing data from the Parkes radio telescope on the coincident young pulsar J1747-2958. We find that G359.23-0.82 is a very luminous X-ray source (L_X [0.5-8.0 keV] = 5e34 ergs/s for a distance of 5 kpc), whose morphology consists of a bright head coincident with PSR J1747-2958, plus a 45"-long narrow tail whose power-law spectrum steepens with distance from the pulsar. We thus confirm that G359.23-0.82 is a bow-shock pulsar wind nebula powered by PSR J1747-2958; the nebular stand-off distance implies that the pulsar is moving with a Mach number of ~60, suggesting a space velocity ~600 km/s through gas of density ~0.3 cm^-3. We combine the theory of ion-dominated pulsar winds with hydrodynamic simulations of pulsar bow shocks to show that a bright elongated X-ray and radio feature extending 10'' behind the pulsar represents the surface of the wind termination shock. The X-ray and radio "trails" seen in other pulsar bow shocks may similarly represent the surface of the termination shock, rather than particles in the postshock flow as is usually argued. The tail of the Mouse contains two components: a relatively broad region seen only at radio wavelengths, and a narrow region seen in both radio and X-rays. We propose that the former represents material flowing from the wind shock ahead of the pulsar's motion, while the latter corresponds to more weakly magnetized material streaming from the backward termination shock. This study represents the first consistent attempt to apply our understanding of "Crab-like" nebulae to the growing group of bow shocks around high-velocity pulsars.

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arXiv2004

Unusual glitch behaviours of two young pulsars

In this paper we report unusual glitches in two young pulsars, PSR J1825-0935 (B1822-09) and PSR J1835-1106. For PSR J1825-0935, a slow glitch characterised by a temporary decrease in the slowdown rate occurred between 2000 December 31 to 2001 December 6. This event resulted in a permanent increase in frequency with fractional size $Δν/ν\sim31.2(2)\times10^{-9}$, however little effect remained in slowdown rate. The glitch in PSR J1835-1106 occurred abruptly in November 2001 (MJD 52220\pm3) with $Δν/ν\sim14.6(4)\times10^{-9}$ and little or no change in the slow-down rate. A significant change in $\ddotν$ apparently occurred at the glitch with $\ddotν$ having opposite sign for the pre- and post-glitch data.

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arXiv2004

The Very Young Radio Pulsar J1357-6429

We report the discovery of a radio pulsar with a characteristic age of 7300 years, making it one of the 10 apparently youngest Galactic pulsars known. PSR J1357-6429, with a spin period of P = 166 ms and spin-down luminosity of 3.1e36 ergs/s, was detected during the Parkes multibeam survey of the Galactic plane. We have measured a large rotational glitch in this pulsar, with Delta P/P = -2.4e-6, similar in magnitude to those experienced occasionally by the Vela pulsar. At a nominal distance of only ~ 2.5 kpc, based on the measured free electron column density of 127 pc/cc and the electron distribution model of Cordes & Lazio, this may be, after the Crab, the nearest very young pulsar known. The pulsar is located near the radio supernova remnant candidate G309.8-2.6.

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arXiv2004

The Parkes multibeam pulsar survey: IV. Discovery of 180 pulsars and parameters for 281 previously known pulsars

The Parkes multibeam pulsar survey has led to the discovery of more than 700 pulsars. In this paper, we provide timing solutions, flux densities and pulse profiles for 180 of these new discoveries. Two pulsars, PSRs J1736-2843 and J1847-0130 have rotational periods P > 6s and are therefore among the slowest rotating radio pulsars known. Conversely, with P = 1.8ms, PSR J1843-1113 has the third shortest period of pulsars currently known. This pulsar and PSR J1905+0400 (P = 3.8ms) are both solitary. We also provide orbital parameters for a new binary system, PSR J1420-5625, which has P = 34ms, an orbital period of 40 days and a minimum companion mass of 0.4 solar masses. The 10 degree-wide strip along the Galactic plane that was surveyed is known to contain 264 radio pulsars that were discovered prior to the multibeam pulsar survey. We have redetected almost all of these pulsars and provide new dispersion measure values and flux densities at 20cm for the redetected pulsars.

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arXiv2004

The Highly Relativistic Binary Pulsar PSR J0737-3039A: Discovery and Implications

PSR J0737-3039A is a millisecond pulsar with a spin period of 22.7 ms included in a double-neutron star system with an orbital period of 2.4 hrs. Its companion has also been detected as a radio pulsar, making this binary the first known double-pulsar system. Its discovery has important implications for relativistic gravity tests, gravitational wave detection and plasma physics. Here we will shortly describe the discovery of the first pulsar in this unique system and present the first results obtained by follow-up studies.

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arXiv2004

The double pulsar -- A new testbed for relativistic gravity

The first ever double pulsar, discovered by our team a few months ago, consists of two pulsars, one with period of 22 ms and the other with a period of 2.7 s. This binary system with a period of only 2.4-hr provides a truly unique laboratory for relativistic gravitational physics. In this contribution we summarize the published results and look at the prospects of future observations.

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