Search

We investigate the birth and evolution of isolated radio pulsars using a population synthesis method, modeling the birth properties of the pulsars, their time evolution, and their detection in the Parkes and Swinburne Multibeam (MB) surveys. Together, the Parkes and Swinburne MB surveys [1, 2] have detected nearly 2/3 of the known pulsars and provide a remarkably homogeneous sample to compare with simulations. New proper motion measurements [3, 4] and an improved model of the distribution of free electrons in the interstellar medium, NE2001 [5], also make revisiting these issues particularly worthwhile. We present a simple population model that reproduces the actual observations well, and consider others that fail. We conclude that: pulsars are born in the spiral arms, with the birthrate of 2.8±0.5 pulsars/century peaking at a distance ∼3 kpc from the Galactic centre, and with mean initial speed of 380−60+40 km s−1; the birth spin period distribution extends to several hundred milliseconds, with no eviden...

Anomalous X‐ray Pulsars are believed to be magnetars: young, isolated neutron stars powered by a large magnetic energy reservoir. Here, we review recent observational progress on five anomalous X‐ray pulsars based on a 10‐year long monitoring project done using the Rossi X‐Ray Timing Explorer (RXTE). In particular, we discuss timing behavior including glitches, radiative variability including bursts, pulsed flux changes, and pulse profile changes. We compare the timing properties to those of regular rotation‐powered pulsars, and we consider the observed radiative phenomena in the context of the magnetar model.

PSR J0205+6449 is a young, rotation‐powered pulsar located at the centre of the SNR 3C 58, widely believed to be the remnant of the historical supernova SN 1181. The neutron star is cooler than expected from standard cooling models [1] and the pulsar, though it has a very high spin‐down luminosity of Ė = 2.6×1037 ergs/s, has very low radio (L1400∼0.5 mJy kpc2 [2]) and X‐ray luminosities (LX = 2.06×1032 ergs/s [3]). We present 4 yrs of timing data spanning 5 yrs obtained with the Rossi X‐ray Timing Explorer, the Jodrell Bank Observatory and the Green Bank Telescope. We present phase‐coherent timing analyses showing significant timing noise that prevents a measurement of the ‘braking index’. In addition, we present two glitches observed in the source and discuss implications for the age and temperature of the neutron star.

The double pulsar system exhibits unique and spectacular eclipses when pulsar A passes behind pulsar B. We present 3.5 years of eclipse monitoring which provides an unprecedented way of probing pulsar magnetospheres, geometric orientation as well as testing general relativity The eclipse light curve of pulsar A has a rich phenomenology. This includes little observed radio frequency dependence and periodic flux modulations in phase with the rotation of pulsar B, which allow the flux to reach uneclipsed levels in narrow windows. Over the monitoring period, the eclipse profile noticeably changed and we observe a modification in the modulation behavior. We quantitatively analyzed the data using the magnetospheric synchrotron absorption eclipse model proposed by Lyutikov and Thompson under the assumption of a simple dipolar magnetic field geometry The success of the model at reproducing the eclipse profile indicates that the magnetic field configuration is mainly dipolar at a distance of about 0.1 light‐cylinder radii from pulsar B. Model fitting leads to the determination of pulsar B's geometric orientation. Therefore by investigating the time evolution of the eclipse profile we can quantitatively test the effects of relativistic spin precession on pulsar B, as predicted by general relativity Also, we note some peculiar features in the egress that are not well modelled and could potentially help to understand distortions of the magnetic field at the magnetosphere boundary

Anomalous X-ray pulsars and soft gamma repeaters have recently emerged as a unified class of neutron stars, identified by dramatic X-ray and gamma-ray outbursts and via luminous X-ray pulsations, both thought to be powered by the decay of an enormous internal magnetic field. This "magnetar" hypothesis has raised the question of these objects' physical relationship with conventional rotation-powered pulsars (RPPs). The highest magnetic-field RPPs might therefore be expected to be transition objects between the two populations. The recently reported magnetar-like outburst of PSR J1846-0258, previously thought to be purely rotation-powered, clearly supports this suggestion. Here we review the observational properties of the highest magnetic-field RPPs known, and show some common characteristics that are notable among RPPs, which are plausibly related to their high fields. Using these objects, we consider the evidence for proposed "magneto-thermal evolution" in neutron stars, and argue that while some exists, it is not yet conclusive., 6 pages, 4 figures, Conference proceeding of "ASTROphysics of Neutron Stars 2010 -- a conference in honor of M. Ali Alpar", 2-6 August 2010, Cesme, Izmir, Turkey

The ∼800 yr‐old pulsar PSR J1846‐0258 in the supernova remnant Kes 75 is a unique transition object between rotation‐powered pulsars and magnetars. While it typically behaves as a rotation‐powered pulsar, in 2006 it exhibited a distinctly magnetar‐like outburst accompanied by a large glitch with an unusual over‐recovery. We present X‐ray timing observations taken with the Rossi X‐ray Timing Explorer after the X‐ray outburst and accompanying glitch had recovered. We observe that the braking index of the pulsar, previously measured to be n = 2.65±0.01 has decreased by 18±5%. We also note a persistent increase in the timing noise relative to the pre‐outburst level, reminiscent of behavior previously observed from some magnetars.

Don Backer was a true founding father of pulsar astronomy, a dedicated and passionate scientist who, alongside a career of tremendous and varied scientific accomplishment, was friendly, easy‐going, dignified, and kind. This tribute summarizes Don’s work, highlighting his many contributions to pulsar astronomy and other fields.

We report on four Chandra observations of the high‐magnetic‐field pulsar J1718–3718 taken in 2009 as well as a re‐analysis of 2002 Chandra observations. We detect clear pulsations at the pulsar’s period in the 2009 data. We found that the pulsar’s X‐ray radiation is mostly thermal emission with a blackbody temperature of 186−18+ 19 eV. The pulsar’s properties are compared to that of some high‐magnetic‐field pulsars and normal pulsars. Implications of our findings are discussed.

Recently, Vink & Bamba (2009) detected extended emission around the magnetar 1E 1547.0–5408 in quiescence and characterized it as the result of a pulsar wind nebula (PWN). From analysis of a February 2010 XMM‐Newton observation of the source, as well as three archival XMM‐Newton observations, we confirm the detection of extended emission. However, we find that its X‐ray flux is highly variable and tightly correlated with the X‐ray flux of the magnetar itself. We conclude that it is most likely due to a dust‐scattering halo and not a PWN as previously claimed.

Outflows in Active Galactic Nuclei (AGN) play an important role in the evolution of their host galaxy and on the enrichment of the intergalactic medium. In the X‐ray range, the outflows appear as a warm absorber (WA) gas displaying high bulk velocities.The Absorption Measure Distribution (AMD) method provides a new handle on constraining the physics of the WA. Here, we report on the theoretical interpretation of an AMD analysis of the Seyfert galaxy NGC 3783. Computations in constant total pressure performed with the transfer‐photoionization code TITAN allow us to reproduce the WA gas ionic column‐densities by adjusting some important plasma parameters, e.g., the ionization parameter (ξ), the total column density (NH) or the amount of micro‐turbulence.Results from both the AMD method and the TITAN code suggest the presence of a region where thermal instabilities are observed. This is compatible with the hypothesis of the WA being a clumpy, two‐phase medium with colder, dense clouds embedded in a hotter, d...

A mechanism of generation of a toroidal component of large scale magnetic field, leading to the reconstruction of the pulsar magnetospheres is presented. In order to understand twisting of magnetic field lines, we investigate kinematics of a plasma stream rotating in the pulsar magnetosphere. Studying an exact set of equations describing the behavior of relativistic plasma flows, the increment of the curvature drift instability is derived, and estimated for $1s$ pulsars. It is shown that a new parametric mechanism is very efficient and can explain rotation energy pumping in the pulsar magnetospheres., Comment: 6 pages, 2 figures

In this work we explore the idea that the high frequency QPOs observed in LMXBs may be explained as a resonant coupling between the neutron star spin and epicyclic modes of accretion disk oscillations. We propose a new model for these QPOs based on forced oscillations induced in the accretion disk due to a stellar asymmetric rotating gravitational or magnetic field. It is shown that particles evolving in a rotating non-axisymmetric field are subject to three kinds of resonances: a corotation resonance, a Lindblad resonance due to a driving force, and a parametric resonance due to the time varying epicyclic frequencies. These results are extends by means of 2D numerical simulations of a simplified version of the accretion disk. The simulations are performed for the Newtonian gravitational potential, as well as for a pseudo-general relativistic potential, which enables us to explore the behavior of the resonances around both rotating neutron stars and black holes. Density perturbations are only significant in the region located close to the inner edge of the disk near the ISCO where the gravitational or magnetic perturbation is maximal. It is argued that the nearly periodic motion induced in the disk will produce high quality factor QPOs. Finally, applying this model to a typical neutron star, we found that the strongest response occurs when the frequency difference of the two modes equals either the spin frequency (for "slow rotators") or half of it (for "fast rotators"). The two main excited modes may both be connected to vertical oscillations of the disk. We emphasize that strong gravity is not needed to excite the modes., Comment: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.189-192

The emission of PSR B0656+14 can be characterized by two separate populations of highly linearly polarized pulses: bright pulses have a narrow spiky appearance consisting of short quasi‐periodic bursts of emission with microstructure, in contrast to the underlying weaker broad pulses. The spiky pulses tend to appear in clusters which arise and dissipate over about 10 periods. We demonstrate that the spiky emission builds a narrow and peaked profile, whereas the weak emission produces a broad hump, which is largely responsible for the shoulders in the total emission profiles at both high and low frequencies. Simultaneous Arecibo Observatory and Westerbork observations further assist us in understanding the emission of this important pulsar. The recently discovered rotating‐radio‐transient (RRAT) sources are characterized by very bright radio bursts that occur periodically but very infrequently. We find bursts with the same characteristics in B0656+14. These bursts represent pulses from the bright end of an...

The isolated neutron star (INS) RX J1308.6+2127 has been observed with Chandra and XMM‐Newton several times between 2000 and 2007. The six most recent XMM‐Newton observations are part of a monitoring campaign we initiated to study the long‐term temporal and spectral properties of INSs. The primary goal of this investigation is to better quantify the similarities and differences between INSs and magnetar candidates (i.e. Anomalous X‐ray Pulsars and Soft Gamma Repeaters) in terms of their spectral and temporal variability. Here, we present our analysis of the current data set and show that (i) the energy spectrum is well modeled by a blackbody with two absorption lines, (ii) the spectral parameters do not show significant time variability over the last seven years, (iii) the pulse profile is strongly energy dependent, but stationary, and (iv) the pulse frequency evolution is consistent with monotonic spin‐down. Our spectral and temporal results are consistent with earlier analyses by Schwope et al. [8] and Kaplan and van Kerkwijk [5], respectively. The inclusion of the new monitoring data provides more precise constraints on both spectral and temporal parameters of this INS. For isolated neutron stars whose X‐ray emission is not powered by spin‐down (INSs, AXPs and SGRs), RX J1308.6+2127 is among the most stable members.

We investigate the number and type of pulsars that will be discovered with the low-frequency radio telescope LOFAR. We consider different search strategies for the Galaxy, for globular clusters and for galaxies other than our own. We show an all-sky Galactic survey can be optimally carried out by incoherently combining the LOFAR stations. In a 60-day all-sky Galactic survey LOFAR can find over a thousand pulsars, probing the local pulsar population to a very deep luminosity limit. For targets of smaller angular size, globular clusters and galaxies, the LOFAR stations can be combined coherently, making use of the full sensitivity. Searches of nearby northern-sky globular clusters can find large numbers of low luminosity millisecond pulsars (eg. over 10 new millisecond pulsars in a 10-hour observation of M15). If the pulsar population in nearby galaxies is similar to that of the Milky Way, a 10-hour observation could find the 10 brightest pulsars in M33, or pulsars in other galaxies out to a distance of 1.2Mpc., Comment: Proceedings of "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More" (12-17 August 2007 at McGill, Montreal Canada)

The pulsar radio emission mechanism has yet to be identified unambiguously. The counter‐streaming instability is a possible wave growth mechanism, but the growth rate in conventional models is too low. Here we argue that the growth rate in an oscillating model of the pulsar magnetosphere is much higher than in conventional models, and might account for the observed emission.

The Johnston et al. (2006) demonstration that natal supernovae “kinks” tend to orient a pulsar's rotation axis Ω with its proper‐motion direction Aν potentially provides the important possibility of determining how pulsar radiation is polarized with respect to the projected magnetic field direction. Although orthogonal polarization mode (OPM) emission has been detected in most pulsars, heretofore no means has been available to fix its absolute direction. Were we thus able to distinguish the OPM orientation, one or the other could be associated with the O or X propagation mode and the implications explored physically. Then, if the O‐mode displacements are in the expected direction, magnetospheric refraction provides a very plausible mechanism. Concretely, the outer edges of conal profiles are almost always highly depolarized through the incoherent mixing of roughly equal OPM levels—requiring them to be offset in both magnetic colatitude and longitude. We inquire whether these differential OPM offsets resul...

I present archival data of the dipping LMXB systems, XB 1916–053, XB 1323–619, X 1624–490, and 4U 1746–371 obtained by the ISGRI and JEM‐X detectors on‐board the INTEGRAL Observatory. The spectral parameters derived from the fits to the data are consistent with hot coronal regions in these systems where the electron temperatures are in a range 4.9–18.8 keV with the exception of XB 1323‐62 having an unbounded temperature. The optical depth to Compton scattering, τ is low and consistent with electron densities ne

A method is presented for including the time‐delays, Doppler effects and oblateness of a rapidly rotating neutron star when fitting X‐ray light curves. Doppler effects and time‐delays are previously known to be essential. We find that the oblateness induced by rotation at frequencies above 300 Hz produces a geometric effect which needs to be accounted for when modelling light curves to extract constraints on the neutron star's mass and radius. The method is applied to model the light curves of the ms pulsar: SAXJ1808‐3658. The results of the modeling are discussed and the resulting constraints on mass and radius of the neutron stars.

GLAST will open a window on the galactic neutron star population and a unique opportunity to understand the pulsar emission mechanism. We will review the general capabilities of GLAST and the expected impact on our understanding on the physics of the emission mechanism of pulsars.

At the end of the EGRET mission, the only firmly identified sources of GeV emission in our Galaxy were a handful of young pulsars and a solar flare. With the recent launch of AGILE and the imminent launch of GLAST, the sources that EGRET saw will again be studied in γ‐rays. We review the multiwavelength observations of the error boxes of Galactic EGRET sources to see what types of sources this new generation of γ‐ray telescopes will be studying. I note that most, if not all, of the sources seem to be related to pulsars. Several are probably radio pulsars not known during the time of EGRET. Others are radio‐quiet pulsars like Geminga. Still others are probably the product of a pulsar wind interacting with a dense environment. The rest seem to be coincident with things associated with the birth of pulsars i.e. supernova remnants, molecular clouds, and massive star associations.

We have carried out a deep search for radio pulsed emission from the accreting millisecond pulsar XTE J0929‐314 using the Parkes radio telescope. In order to overcome the possible free‐free absorption, caused by matter surrounding the system during the quiescent phase, we performed the observations at high frequencies. No radio pulsations were found down to a limit of 68 μJy at 6.5 GHz and of 26 μJy at 8.5 GHz.We analysed the possible reasons for the non‐detection concluding that beaming factor and intrinsic low luminosity are the most likely explanations.

In a magnetar, the dominant magnetospheric source of opacity for soft X‐ray photons is resonant cyclotron scattering. The differential cross‐section for this process is strongly angle‐dependent, which implies that geometry plays a key role in shaping spectra and pulse profiles as measured by a distant observer. Here provide an overview of our work on multidimensional simulations involving the transfer of X‐ray photons through a twisted magnetosphere, and discuss the generic features of the resulting spectra and pulse profiles, with their dependence on the particle energy distribution.

We present preliminary results on the spectral modeling of magnetars' X‐ray emission through a resonant cyclotron scattering model. We fit the soft and hard X‐ray spectrum of all magnetars with a main component representing a thermal emission from the neutron star surface which scatters (through a resonant cyclotron scattering process) on a slab of mildly relativistic magnetospheric electrons. Here we present the results obtained for the 0.5–200 keV (XMM–Newton+INTEGRAL) spectrum of the anomalous X‐ray pulsar 1E 1841–045, and the 0.5–10 keV (XMM–Newton) variable spectrum of the transient magnetar XTE J1810–197.

In this paper we report multifrequency single pulse polarization observations of the PSR B0329+54 normal mode from the Giant Meterwave Radio Telescope (GMRT) at 325 and 610 MHz and the Effelsberg Observatory at 2695 MHz. Towards the central part of the polarization position‐angle traverse there is an unusual “arc”‐like structure, which is comprised of a broadband “kink” and a frequency‐dependent “spot.” The features are intimately connected with the intensity dependence of the core component: the stronger emission arrives earlier and its linear polarization is displaced farther along the “kink”. Moreover, at high intensities, the circular polarization is LH/RH antisymmetric; the nearly complete RH circular is characteristic of the weaker, later core subpulses. We find that the “kink” emission is associated with the extraordinary (X) propagation mode, and hence propagation effects do not appear capable of producing the core component's broadband, intensity‐dependent emission. Rather, the overall evidence points to a largely geometric interpretation in which the “kink” provides a rare glimpse of the accelerating cascade or height‐dependent amplifier responsible for the core radiation.

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., Comment: 5 page, 2 figures; To appear in the conference proceedings "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17, 2007, at McGill University, Montreal, Canada. Version with full-resolution figures can be found at http://www.phas.ubc.ca/~ferdman/ferdman.0737_geo.full.ps.gz; typos corrected, some rewording, and references added

With a peak luminosity of ~10^47 erg/s, the December 27th 2004 giant flare from SGR1806-20 would have been visible by BATSE (the Burst and Transient Source Experiment) out to ~50 Mpc. It is thus plausible that some fraction of the short duration Gamma-Ray Bursts (sGRBs) in the BATSE catalogue were due to extragalactic magnetar giant flares. According to the most widely accepted current models, the remaining BATSE sGRBs were most likely produced by compact object (neutron star-neutron star or neutron star-black hole) mergers with intrinsically higher luminosities. Previously, by examining correlations on the sky between BATSE sGRBs and galaxies within 155 Mpc, we placed limits on the proportion of nearby sGRBs. Here, we examine the redshift distribution of sGRBs produced by assuming both one and two populations of progenitor with separate Luminosity Functions (LFs). Using the local Galactic SGR giant flare rate and theoretical NS-NS merger rates evolved according to well-known Star Formation Rate parameterisations, we constrain the predicted distributions by BATSE sGRB overall number counts. We show that only a dual population consisting of both SGR giant flares and NS-NS mergers can reproduce the likely local distribution of sGRBs as well as the overall number counts. In addition, the best fit LF parameters of both sub-populations are in good agreement with observed luminosities., 3 pages, 7 figures. To be included in the proceedings of "40 Years of Pulsars" held at McGill University, Montreal, 2007. Proceedings to be published by American Institute of Physics

Using public data from the XMM‐Newton archive we have discovered pulsations at 7 s in the isolated neutron star RX J1856.5–3754, thus confirming that this source is similar to the other six thermally emitting, nearby neutron stars discovered in soft X‐rays with ROSAT. The pulsations are detected in eight XMM‐Newton observations spanning from April 2002 to March 2007. Using the two latest observations, reported here for the first time, we derive a new upper limit of Ṗ

Millisecond pulsars in southern globular clusters have been regularly observed for timing pourposes with the Parkes radio telescope. To date, several pulsars have data spanning more than 6 years, and their peculiarities are now recognisable via their timing analysis. In this paper we briefly summarise the state of the art of the timing for the eclipsing binary PSR J1701‐3006B in the clobular cluster NGC6266 and for all the millisecond pulsars in the globualr cluster NGC6752.

Basic theoretical ideas about the origin of the pulsar emission across the electromagnetic spectrum are reviewed.

The spin axis of some pulsars precesses due to body asymmetries, binary companions, or other effects. The spin precession causes our line of sight to drift slowly across the emission beam, leading to secular changes in the observed pulse profile. Studies of these variations thus provide a unique tool to reveal the two‐dimensional structure of the emission beam.Weisberg & Taylor [1, 2] found that an hourglass‐shaped beam was required in order to successfully model their observations of pulse profile changes in the binary pulsar B1913+16, which undergoes relativistic geodetic spin precession. We define here a novel coordinate system to aid in visualization of the observing geometry. We then present a circular beam model and show that this simple model can exhibit quite complicated pulse profile changes. We revisit the question of whether elaborate beam models are needed to explain the observations of PSR B1913+16. We find that the circular model qualitatively matches the data for B1913+16, but that additional parameters are needed for a good fit.

One of the primary goals when studying stellar systems with neutron stars has been to reveal the physical properties of progenitors and understand how neutron star spins and birth kicks are determined. Over the years a consensus understanding had been developed, but recently some of the basic elements of this understanding are being challenged by current observations of some binary systems and their theoretical interpretation. In what follows we review such recent developments and highlight how they are interconnected; we particularly emphasize some of the assumptions and caveats of theoretical interpretations and examine their validity (e.g., in connection to the unknown radial velocities of pulsars or the nuances of multi-dimensional statistical analysis). The emerging picture does not erase our earlier understanding; instead it broadens it as it reveals additional pathways for neutron star formation and evolution: neutron stars probably form at the end of both core collapse of Fe cores of massive stars and electron-capture supernovae of ONeMg cores of lower-mass stars; birth kicks are required to be high (well in excess of 100 km/s) for some neutron stars and low (< 100 km/s) for others depending on the formation process; and spin up may occur not just through Roche-lobe overflow but also through wind accretion or phases of hypercritical accretion during common envelope evolution., 9 pages,4 figures, proceedings paper for 40 Years of Pulsars Conference

Possible origins of the magnetic fields of neutron stars include inheritance from the main sequence progenitor and dynamo action at some stage of evolution of progenitor. Inheritance is not sufficient to explain the fields of magnetars. Energetic considerations point to differential rotation in the final stages of core collapse process as the most likely source of field generation, at least for magnetars. A runaway phase of exponential growth is needed to achieve sufficient field amplification during relevant phase of core collapse; it can probably be provided by a some form of magnetorotational instability. Once formed in core collapse, the field is in danger of decaying again by magnetic instabilities. The evolution of a magnetic field in a newly formed neutron star is discussed, with emphasis on the existence of stable equilibrium configurations as end products of this evolution, and the role of magnetic helicity in their existence., Review to appear in "40 years of pulsars", ed. A. Cumming, AIP. v2: Updated references and discussion section. v3: reference added

Our understanding of Pulsar Wind Nebulae (PWNe), has greatly improved in the last years thanks to unprecedented high resolution images taken from the HUBBLE, CHANDRA and XMM satellites. The discovery of complex but similar inner features, with the presence of unexpected axisymmetric rings and jets, has prompted a new investigation into the dynamics of the interaction of the pulsar winds with the surrounding SNR, which, thanks to the improvement in the computational resources, has let to a better understanding of the properties of these objects. On the other hand the discovery of non-thermal emission from bow shock PWNe, and of systems with a complex interaction between pulsar and SNR, has led to the development of more reliable evolutionary models. I will review the standard theory of PWNe, their evolution, and the current status in the modeling of their emission properties, in particular I will show that our evolutionary models are able to describe the observations, and that the X-ray emission can now be reproduced with sufficient accuracy, to the point that we can use these nebulae to investigate fundamental issues as the properties of relativistic outflows and particle acceleration., 9 page, 5 figures, Proceeding of the conference "40 Years of Pulsars", 12-17 August 2007, Montreal, Canada. (figures are not properly displayed in .ps or .pdf version please download archive for them)

PSR J1119–6127 is a young, yet slow, rotation‐powered radio and X‐ray pulsar associated with SNR G292.2–0.5. Its inferred high surface magnetic field of B = 4.1×1013 Gauss is interestingly close to the critical QED value above which pulsars are believed to enter the magnetar regime. In 2003, we have detected the X‐ray counterpart of the radio pulsar with Chandra and provided the first evidence for a compact and faint pulsar wind nebula (PWN, [3]). We here present new Chandra observations of the pulsar, thus providing a deep (∼140 ksec total) exposure. The observations allowed 1) a confirmation of the PWN detection, 2) a high‐resolution imaging study revealing the structure of the PWN, and 3) for the 1st time a spectroscopic study of the pulsar independently from its surrounding nebula. We discuss the implications of our study to our understanding of this unique system and more generally to the manifestation of high magnetic field radio pulsars in X‐rays, in comparison with the more ‘classical’ rotation‐po...

The Parkes 20‐cm Multibeam Pulsar search system has been used by several groups of astronomers who have to date discovered between them no fewer than 953 pulsars, more than the 822 discovered by all other searches combined.

We report here on recent progress in understanding the birth conditions of neutron stars and the way how supernovae explode. More sophisticated numerical models have led to the discovery of new phenomena in the supernova core, for example a generic hydrodynamic instability of the stagnant supernova shock against low-mode nonradial deformation and the excitation of gravity-wave activity in the surface and core of the nascent neutron star. Both can have supportive or decisive influence on the inauguration of the explosion, the former by improving the conditions for energy deposition by neutrino heating in the postshock gas, the latter by supplying the developing blast with a flux of acoustic power that adds to the energy transfer by neutrinos. While recent two-dimensional models suggest that the neutrino-driven mechanism may be viable for stars from about 8 solar masses to at least 15 solar masses, acoustic energy input has been advocated as an alternative if neutrino heating fails. Magnetohydrodynamic effects constitute another way to trigger explosions in connection with the collapse of sufficiently rapidly rotating stellar cores, perhaps linked to the birth of magnetars. The global explosion asymmetries seen in the recent simulations offer an explanation of even the highest measured kick velocities of young neutron stars., Comment: 10 pages, 8 figures, 19 ps files; to be published in Proc. of Conf. "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17, 2007, McGill Univ., Montreal, Canada; high-resolution images can be obtained upon request; incorrect panel in fig.8 replaced

Gravitational waves passing the Earth induce signals in pulsar timing residuals that are potentially detectable using modern pulsar timing observations. It has been predicted that merging supermassive black hole systems will cause an isotropic background of gravitational waves. Pulsar timing observations will soon be able to provide useful constraints on models for its formation. Future experiments will either detect this background or rule out all existing models. Various cosmic string theories and inflationary era models have also been proposed that predict gravitational wave backgrounds, but the amplitude of the background in these models is not well constrained. We review new techniques to limit the existence of any gravitational wave background, provide results obtained using data taken as part of the Parkes Pulsar Timing Array project and describe the implications of these new upper limits.

During accretion, a neutron star (NS) is spun up as angular momentum is transported through its liquid surface layers. We study the resulting differentially rotating profile, focusing on the impact this has for type I X-ray bursts. The viscous heating is found to be negligible, but turbulent mixing can be activated. Mixing has the greatest impact when the buoyancy at the compositional discontinuity between accreted matter and ashes is overcome. This occurs preferentially at high accretion rates or low spin frequencies and may depend on the ash composition from the previous burst. We then find two new regimes of burning. The first is ignition in a layer containing a mixture of heavier elements with recurrence times as short as ~5-30 minutes, similar to short recurrence time bursts. When mixing is sufficiently strong, a second regime is found where accreted helium mixes deep enough to burn stably, quenching X-ray bursts altogether. The carbon-rich material produced by stable helium burning would be important for triggering and fueling superbursts., 3 pages, 3 figures. To appear in the proceedings of "Forty Years of Pulsars: Millisecond Pulsars, Magnetars and More" held in Montreal, Canada, August 12-17, 2007

The magnetospheric plasma distribution in the vicinity of a pulsar at various inclination angles is investigated using a new relativistic, parallel 3D Particle‐In‐Cell (PIC) code, DYMPHNA3D. Our initial simulation results are presented here. These show similar solutions to those obtained from previous numerical simulations, which show the fundamental plasma distribution in the vicinity of an aligned rotating neutron star to consist of two polar domes and an equatorial torus of trapped non‐neutral plasma of opposite sign, separated by a vacuum gap. Furthermore, our code allows for off‐axis simulations and we have we have found that this plasma distribution collapses into a quad‐lobe charge‐separated non‐neutral distribution in the case of an orthogonal rotator, bearing a stark resemblance to that predicted theoretically by Parish in 1974, [11], with the exception that in our results, the plasma remains trapped close to the stellar surface by the force‐free (E⋅B = 0) surfaces observed in this region.

New simultaneous observations of B0943+10 were carried out at the Pushchino Radio Astronomy Observatory with the DKR‐1000 telescope at 42 and 62 MHz and the BSA at 112 MHz. These illuminate the low frequency behavior of the pulsar after onset of the pulsar's ‘B’ mode. Changes in both the “carousel” circulation time and profile form were detected at the lower frequencies, but the latter were somewhat less dramatic than at meter wavelengths.

International audience; The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST) will see first light in mid-2008, and is expected to discover scores of pulsars in GeV γ-rays. For most, days to weeks will separate recorded gamma events. Rotation parameters provided by radio or X-ray instruments permit pulsation searches with greater sensitivity than what the LAT can achieve alone. But the gamma pulsar candidates tend to be the young ones with large timing noise, meaning that the ephemerides need to be updated relatively frequently over the years of the GLAST mission. We describe the criteria used to identify gamma pulsar candidates, and the observation campaign underway to provide ephemerides useful for the pulsed gamma searches, with some illustrations of the LAT's capabilities.

We briefly review our current understanding of the various evolutionary channels that lead to the formation of wide Binary Millisecond Pulsars (bMSPs). Depending on the initial conditions at the onset of Roche lobe overflow, there is a very sharp bifurcation in the evolution of the orbital periods of these systems. Binary systems just below the bifurcation limit can evolve to become ultracompact systems (e.g., accretion‐powered MSPs), while those above the limit will evolve to form bMSPs with periods of between approximately one day to 1000 days. One of the interesting features in the distribution of Galactic bMSPs is an orbital period gap of between ∼20 and 60 days. We show that if the radio‐ejection mechanism is efficient in preventing further accretion onto the spun‐up neutron star, then the paucity of bMSPs in this period range can naturally be explained. The dependence of the orbital period distribution on the metallicity of the binary system is also investigated.

We present refined neutron star masses measured in an Arecibo observing campaign of two binary radio pulsars, and we summarize the masses of the binary radio pulsar population.For PSR J0621+1002, we find the relativistic rate of advance of periastron to be ω = 0.0105±0.0002° yr−1, implying a total system mass (pulsar plus companion) of m1+m2 = 2.37±0.12 M⊙. Combined with the non‐detection of Shapiro delay and an assumption that the companion star is a white dwarf, we constrain the mass of this pulsar to be m1 = 1.70−0.17+0.10 M⊙ (68% confidence), in agreement with previous measurements of this pulsar, but with higher precision.For PSR 0751+1807, we find the rate of orbital decay due to emission of gravitational radiation to be Ṗb = −(3.1±0.5)×10−14. Combining this with detection of Shapiro delay yields a pulsar mass of 1.26±0.14 M⊙ (68% confidence), much smaller than the previously reported value of 2.1±0.2 M⊙. We discuss the reason for this discrepancy.We present a summary of masses if pulsars in the Ga...

Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests of the theoretical models developed based on past discoveries. With its greatly improved sensitivity, better angular resolution, and larger energy reach than older instruments, GLAST LAT should detect dozens to hundreds of new gamma-ray pulsars and measure luminosities, light curves, and phase-resolved spectra with unprecedented resolution. It will also have the potential to find radio-quiet pulsars like Geminga, using blind search techniques. Cooperation with radio and X-ray pulsar astronomers is an important aspect of the LAT team's planning for pulsar studies., 8 pages, 5 figures. To appear in the proceedings of "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17, 2007, McGill University, Montreal, Canada

The main objectives of modeling the Galactic pulsar population are (i) to understand underlying properties of various pulsar subclasses, and (ii) to probe physical conditions relevant to the formation and evolution of these objects. A theoretical approach is useful to explore various stellar populations, but introduces large systematic uncertainties in results. An empirical approach is known to be more reliable, but is limited only to known populations. Traditionally, the pulsar population studies focused on isolated, slowly rotating ‘normal’ pulsars that are the majority of the known pulsars. With improved pulsar search techniques and more sensitive instruments, the known pulsar sample has been greatly expanding, both in quality and quantity, over the past 40 years. The increased number of pulsar sample allows more rigorous statistical analysis on the normal population. Moreover, there are many new populations to be studied, such as relativistic pulsar binaries, millisecond pulsars, or pulsars in globular clusters.

A large sample of about two hundred pulsars have been observed to study their subpulse modulation at an observing wavelength of (when achievable) both 21 and 92 cm using the Westerbork Synthesis Radio Telescope. For 57 pulsars drifting subpulses are discovered for the first time and are confirmed for many others. This leads to the conclusion that it could well be that the drifting subpulse mechanism is an intrinsic property of the emission mechanism itself, although for some pulsars it is difficult or impossible to detect. It appears that the youngest pulsars have the most disordered subpulses and the subpulses become more and more organized into drifting subpulses as the pulsar ages. Drifting subpulses are in general found at both frequencies and the measured values of P3 at the two frequencies are highly correlated, showing the broadband nature of this phenomenon. Also the modulation indices measured at the two frequencies are clearly correlated, although at 92 cm they are on average possibly higher. The correlations with the modulation indices are argued to be consistent with the picture in which the radio emission is composed out of a drifting subpulse signal plus a quasi-steady signal which becomes, on average, stronger at high observing frequencies. There is no obvious correlation found between P3 and the pulsar age (or any other pulsar parameter) contrary to reports in the past., Proceedings of the 40 Years of Pulsars: Millisecond Pulsars, Magnetars and More conference in Montreal

The unprecedented spatial resolution of the Chandra observatory opens the possibility to detect with relatively high accuracy proper motions at X-ray wavelengths. We have conducted an astrometric study of three of the "Magnificent Seven", the thermally emitting radio quiet isolated neutron stars (INSs) discovered by ROSAT. These three INSs (RX J0420.0-5022, RX J0806.4-4123 and RX J1308.6+2127/RBS 1223) either lack an optical counterpart or have one too faint to be used for astrometric purposes. We obtained ACIS observations 3 to 5 years apart to constrain or measure the displacement of the sources on the X-ray sky using as reference the background of extragalactic or remote galactic X-ray sources. Upper limits of 138 mas/yr and 76 mas/yr on the proper motion of RX J0420.0-5022 and RX J0806.4-4123, respectively, have already been presented in Motch et al. (2007). Here we report the very significant measurement (~ 10 sigma) of the proper motion of the third INS of our program, RX J1308.6+2127/RBS1223. Comparing observations obtained in 2002 and 2007 reveals a displacement of 1.1 arcsec implying a yearly proper motion of 223 mas, the second fastest measured for the ROSAT discovered INSs. The source is rapidly moving away from the galactic plane at a speed which precludes any significant accretion of matter from the interstellar medium. Its transverse velocity of ~ 740 (d/700pc) km/s might be the largest of the "Magnificent Seven" and among the fastest recorded for neutron stars. RX J1308.6+2127/RBS1223 is thus a young high velocity cooling neutron star. The source may have its origin in the closest part of the Scutum OB2 association about 0.8 Myr ago, an age consistent with that expected from cooling curves, but significantly younger than inferred from pulse timing measurements (1.5 Myr)., Comment: 3 pages, 2 figures, proceedings of the conference "40 Years of Pulsars", 12-17 August 2007, Montreal, Canada

We extend the classical minimization sum of completion times problem to the case where the processing times are controllable by allocating a nonrenewable resource. The quality of a solution is measured by two different criteria. The first criterion is the sum of completion times and the second is the total weighted resource consumption. We consider four different problem variations for treating the two criteria. We prove that this problem is NP‐hard for three of the four variations even if all resource consumption weights are equal. However, somewhat surprisingly, the variation of minimizing the integrated objective function is solvable in polynomial time. Although the sum of completion times is arguably the most important scheduling criteria, the complexity of this problem, up to this paper, was an open question for three of the four variations. The results of this research have various implementations, including efficient battery usage on mobile devices such as mobile computer, phones and GPS devices in...