Energetic Pulsars Research Articles

Profile and polarization characteristics of energetic pulsars

In this paper, we compare the characteristics of pulsars with a high spin-down energy-loss rate (E) against those with a low E. We show that the differences in the total intensity pulse morphology between the two classes are in general rather subtle. A much more significant difference is the fractional polarization which is very high for high E pulsars and low for low E pulsars. The E at the transition is very similar to the death line predicted for curvature radiation. This suggests a possible link between high energy and radio emission in pulsars and could imply that γ-ray efficiency is correlated with the degree of linear polarization in the radio band. The degree of circular polarization is in general higher in the second component of doubles, which is possibly caused by the effect of corotation on the curvature of the field lines in the inertial observer frame. The most direct link between the high-energy emission and the radio emission could be the subgroup of pulsars which we call the energetic wide beam pulsars. These young pulsars have very wide profiles with steep edges and are likely to be emitted from a single magnetic pole. The similarities with the high-energy profiles suggest that both types of emission are produced at the same extended height range in the magnetosphere. Alternatively, the beams of the energetic wide beam pulsars could be magnified by propagation effects in the magnetosphere. This would naturally lead to decoupling of the wave modes, which could explain the high degree of linear polarization. As part of this study, we have discovered three previously unknown interpulse pulsars (and we detected one for the first time at 20 cm). We also obtained rotation measures for 18 pulsars whose values had not previously been measured.

The Fermi Gamma-Ray Space Telescope Discovers the Pulsar in the Young Galactic Supernova Remnant CTA 1

Energetic young pulsars and expanding blast waves [supernova remnants (SNRs)] are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 milliseconds and a period derivative of 3.614 x 10(-13) seconds per second. Its characteristic age of 10(4) years is comparable to that estimated for the SNR. We speculate that most unidentified Galactic gamma-ray sources associated with star-forming regions and SNRs are such young pulsars.

DA 495: An Aging Pulsar Wind Nebula

We present a radio continuum study of the pulsar wind nebula (PWN) DA 495 (G65.7+1.2), including images of total intensity and linear polarization from 408 to 10550 MHz based on the Canadian Galactic Plane Survey and observations with the Effelsberg 100 m Radio Telescope. Removal of flux density contributions from a superimposed H II region and from compact extragalactic sources reveals a break in the spectrum of DA 495 at 1.3 GHz, with a spectral index α = − 0.45 ± 0.20 below the break and α = − 0.87 ± 0.10 above it (Sν ∝ να). The spectral break is more than 3 times lower in frequency than the lowest break detected in any other PWN. The break in the spectrum is likely the result of synchrotron cooling, and DA 495, at an age of ~20,000 yr, may have evolved from an object similar to the Vela X nebula, with a similarly energetic pulsar. We find a magnetic field of ~1.3 mG inside the nebula. After correcting for the resulting high internal rotation measure, the magnetic field structure is quite simple, resembling the inner part of a dipole field projected onto the plane of the sky, although a toroidal component is likely also present. The dipole field axis, which should be parallel to the spin axis of the putative pulsar, lies at an angle of ~50° east of the north celestial pole and is pointing away from us toward the southwest. The upper limit for the radio surface brightness of any shell-type supernova remnant emission around DA 495 is Σ1GHz ~ 5.4 × 10−23 W m−2 Hz−1 sr−1 (assuming a radio spectral index of α = − 0.5), lower than the faintest shell-type remnant known to date.

Pulsar wind zone processes in LS 5039

Several γ-ray binaries have been recently detected by the high-energy stereoscopy array (HESS) and the major atmospheric imaging cerenkov (MAGIC) telescope. In at least two cases, their nature is unknown. In this paper we aim to provide the details of a theoretical model of close γ-ray binaries containing a young energetic pulsar as compact object, earlier presented in recent letters. This model includes a detailed account of the system geometry, the angular dependence of processes such as Klein–Nishina inverse Compton and γγ absorption in the anisotropic radiation field of the massive star, and a Monte Carlo simulation of leptonic cascading. We present and derive the used formulae and give all details about their numerical implementation, particularly, on the computation of cascades. In this model, emphasis is put in the processes occurring in the pulsar wind zone of the binary, since, as we show, opacities in this region can be already important for close systems. We provide a detailed study on all relevant opacities and geometrical dependencies along the orbit of binaries, exemplifying with the case of LS 5039. This is used to understand the formation of the very high-energy lightcurve and phase dependent spectrum. For the particular case of LS 5039, we uncover an interesting behavior of the magnitude representing the shock position in the direction to the observer along the orbit, and analyze its impact in the predictions. We show that in the case of LS 5039, the HESS phenomenology is matched by the presented model, and explore the reasons why this happens while discussing future ways of testing the model.

A high-frequency search for radio pulsars in three EGRET error boxes

We present a new survey for pulsars in the error boxes of the low-latitude EGRET sources 3EG J1027−5817, 3EG J1800−2338 and 3EG J1810−1032. Although all of these sources have been covered by previous pulsar surveys, the recent discovery of the young, energetic pulsar PSR J1410−6132 at 6.7 GHz has shown that pulsars of this type can be hidden from low-frequency surveys. Using an observing frequency of 3.1 GHz, we discovered a 91-ms pulsar, PSR J1028−5819, which observations made at the Parkes telescope and the Australia Telescope Compact Array have shown to be young and energetic. We believe this pulsar is likely to be powering the unidentified EGRET source 3EG J1027−5817. Like other energetic pulsars, PSR J1028−5819 is highly linearly polarized, but astonishingly has a pulse duty cycle of only 0.4 per cent, one of the smallest in the entire pulsar catalogue.

PSR J1856+0245: Arecibo Discovery of a Young, Energetic Pulsar Coincident with the TeV γ-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 81 ms, a characteristic age of 21 kyr, and a spin-down luminosity (E) over dot = 4.6 x 10(36) ergs s(-1). 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 ( 100 GeV-100 TeV) 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/(E) over dot = 3.1 % (1-10 TeV, for a distance of 9 kpc), comparable to that observed in similar associations.

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

Abstract We present the discovery of PSR J1410-6132, a 50-ms pulsar found during a high-frequency survey of the Galactic plane, using a seven-beam 6.3-GHz receiver on the 64-m Parkes radio telescope. The pulsar lies within the error box of the unidentified Energetic Gamma Ray Experiment Telescope (EGRET) source 3EG J1410-6147, has a characteristic age of 26 kyr and a spin-down energy of 1037 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 γ-ray efficiency factor of ∼10 per cent is sufficient to power the γ-ray source. We therefore believe that 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.

Multifrequency integrated profiles of pulsars

We have observed a total of 67 pulsars at five frequencies ranging from 243 to 3100 MHz. Observations at the lower frequencies were made at the Giant Metre-Wave Telescope in India and those at higher frequencies at the Parkes Telescope in Australia. We present profiles from 34 of the sample with the best signal-to-noise ratio and the least scattering. The general ‘rules’ of pulsar profiles are seen in the data; profiles get narrower, the polarization fraction declines and outer components become more prominent as the frequency increases. Many counterexamples to these rules are also observed, and pulsars with complex profiles are especially prone to rule breaking. We hypothesize that the location of pulsar emission within the magnetosphere evolves with time as the pulsar spins down. In highly energetic pulsars, the emission comes from a confined range of high altitudes, in the middle range of spin down energies the emission occurs over a wide range of altitudes whereas in pulsars with low spin-down energies it is confined to low down in the magnetosphere.

INTEGRAL observations of PSR J1811−1925 and its associated pulsar wind nebula

Abstract We present spectral measurements made in the soft (20–100 keV) γ-ray band of the region containing the composite supernova remnant G11.2-0.3 and its associated pulsar PSR J1811−1925. Analysis of INTEGRAL/IBIS data allows characterization of the system above 10 keV. The IBIS spectrum is best fitted by a power law having photon index Γ= 1.8+0.4−0.3 and a 20–100 keV flux of 1.5 × 10−11 erg cm−2 s−1. Analysis of archival Chandra data over different energy bands rules out the supernova shell as the site of the soft γ-ray emission while broadband (1–200 keV) spectral analysis strongly indicates that the INTEGRAL/IBIS photons originate in the central zone of the system which contains both the pulsar and its nebula. The composite X-ray and soft γ-ray spectrum indicates that the pulsar provides around half of the emission seen in the soft γ-ray domain; its spectrum is hard with no sign of a cut off up to at least 80 keV. The other half of the emission above 10 keV comes from the pulsar wind nebula; with a Γ= 1.7 its spectrum is softer than that of the pulsar. From the IBIS/ISGRI mosaics we are able to derive 2σ upper limits for the 20–100 keV flux from the location of the nearby TeV source HESS J1809−193 to be 4.8 ×10−12 erg cm−2 s−1. We have also examined the likelihood of an association between PSR J1811−1925 and HESS J1809−193. Although PSR J1811−1925 is the most energetic pulsar in the region, the only one detected above 10 keV and thus a possible source of energy to fuel the TeV fluxes, there is no morphological evidence to support this pairing, making it an unlikely counterpart.

γ-rays from binary system with energetic pulsar and Be star with aspherical wind: PSR B1259−63/SS2883

At least one massive binary system containing an energetic pulsar, PSR B1259−63/SS2883, has been recently detected in the TeV γ -rays by the HESS telescopes. These γ -rays are likely produced by particles accelerated in the vicinity of the pulsar and/or at the pulsar wind shock, in comptonization of soft radiation from the massive star. However, the process of γ -ray production in such systems can be quite complicated due to the anisotropy of the radiation field, complex structure of the pulsar wind termination shock and possible absorption of produced γ -rays which might initiate leptonic cascades. In this paper, we consider in detail all these effects. We calculate the γ -ray light curves and spectra for different geometries of the binary system PSR B1259−63/SS2883 and compare them with the TeV γ -ray observations. We conclude that the leptonic inverse-Compton model, which takes into account the complex structure of the pulsar wind shock due to the aspherical wind of the massive star, can explain the details of the observed γ -ray light curve.

An empirical model for the beams of radio pulsars

Motivated by recent results on the location of the radio emission in pulsar magnetospheres, we have developed a model which can account for the large diversity found in the average profile shapes of pulsars. At the centre of our model lies the idea that radio emission at a particular frequency arises from a wide range of altitudes above the surface of the star, and that it is confined to a region close to the last open field lines. We assert that the radial height range over which emission occurs is responsible for the complex average pulse shapes rather than the transverse (longitudinal) range proposed in most current models. By implementing an abrupt change in the height range to discriminate between young, short-period, highly energetic pulsars and their older counterparts, we obtain the observed transition between the simple and complex average pulse profiles observed in each group respectively. Monte Carlo simulations are used to demonstrate the match of our model to real observations.

Discovery of the Putative Pulsar and Wind Nebula Associated with the TeV Gamma‐Ray Source HESS J1813−178

We present a Chandra X-ray observation of G12.82-0.02, a shell-like radio supernova remnant coincident with the TeV gamma-ray source HESS J1813-178. We resolve the X-ray emission from the colocated Advanced Satellite for Cosmology and Astrophysics (ASCA) source into a point source surrounded by structured diffuse emission that fills the interior of the radio shell. The morphology of the diffuse emission strongly resembles that of a pulsar wind nebula. The spectrum of the compact source is well characterized by a power law with index Γ ≈ 1.3, typical of young and energetic rotation-powered pulsars. For a distance of 4.5 kpc, consistent with the X-ray absorption and an association with the nearby star formation region W33, the 2-10 keV X-ray luminosities of the putative pulsar and nebula are LPSR = 3.2 × 1033 ergs s-1 and LPWN = 1.4 × 1034 ergs s-1, respectively. Both the flux ratio of LPWN/LPSR = 4.3 and the total luminosity of this system predict a pulsar spin-down power of Ė > 1037 ergs s-1, placing it among the 10 most energetic young pulsars in the Galaxy. A deep search for radio pulsations using the Parkes telescope sets an upper limit of ≈0.07 mJy at 1.4 GHz for periods 50 ms. We discuss the energetics of this source and consider briefly the proximity of bright H II regions to this and several other High Energy Stereoscopic System (H.E.S.S.) sources, which may produce their TeV emission via inverse Compton scattering.

HESS J1616−508: likely to be powered by PSR J1617−5055

HESS J1616 _ 508 is one of the brightest emitters in the TeV sky. Recent observations with the IBIS/ISGRI telescope onboard the INTEGRAL spacecraft have revealed that a young, nearby and energetic pulsar, PSR J1617 _ 5055, is a powerful emitter of soft γ-rays in the 20-100 keV domain. In this paper, we present an analysis of all available data from the INTEGRAL, Swift, BeppoSAX and XMM-Newton telescopes with a view to assessing the most likely counterpart to the High Energy Stereoscopic System (HESS) source. We find that the energy source that fuels the X/y-ray emissions is derived from the pulsar, both on the basis of the positional morphology, the timing evidence and the energetics of the system. Likewise the 1.2 per cent of the pulsar's spin-down energy loss needed to power the 0.1-10 TeV emission is also fully consistent with other HESS sources known to be associated with pulsars. The relative sizes of the X/y-ray and very high energy sources are consistent with the expected lifetimes against synchrotron and Compton losses for a single source of parent electrons emitted from the pulsar. We find that no other known object in the vicinity could be reasonably considered as a plausible counterpart to the HESS source. We conclude that there is good evidence to assume that the HESS J1616-508 source is driven by PSR J1617-5055 in which a combination of synchrotron and inverse-Compton processes combine to create the observed morphology of a broad-band emitter from keV to TeV energies.

Flux Densities and Radio Polarization Characteristics of Two Vela-like Pulsars

We report on dual-frequency radio polarimetry observations of two young, energetic pulsars, PSRs J0940-5428 and J1301-6305. These were among the first Vela-like pulsars discovered in the Parkes Multibeam survey. We conducted observations of these pulsars with the Australia Telescope Compact Array (ATCA) at center frequencies of 1384 and 2496 MHz using pulsar gating while preserving full Stokes parameters. After correcting for bandwidth depolarization, we have measured polarization characteristics, flux densities, and rotation measures for these pulsars. The spectral indices derived from the ATCA data are shallow but still consistent with values seen for pulsars of this type. The rotation measures for both pulsars are consistent with those reported recently using data from the Parkes telescope, and both pulsars have highly linearly polarized pulse profiles at both 1384 and 2496 MHz. Our results support a previously noted correlation between high degree of linear polarization, shallow spectral index, and large spin-down luminosity.

X‐Ray Timing Observations of PSR J1930+1852 in the Crab‐like SNR G54.1+0.3

We present new X-ray timing and spectral observations of PSR J1930+1852, the young energetic pulsar at the center of the non-thermal supernova remnant G54.1+0.3. Using data obtained with the Rossi X-ray Timing Explorer and Chandra X-ray observatories we have derived an updated timing ephemeris of the 136 ms pulsar spanning 6 years. During this interval, however, the period evolution shows significant variability from the best fit constant spin-down rate of $\dot P = 7.5112(6) \times 10^{-13}$ s s$^{-1}$, suggesting strong timing noise and/or glitch activity. The X-ray emission is highly pulsed ($71\pm5%$ modulation) and is characterized by an asymmetric, broad profile ($\sim 70%$ duty cycle) which is nearly twice the radio width. The spectrum of the pulsed emission is well fitted with an absorbed power law of photon index $\Gamma = 1.2\pm0.2$; this is marginally harder than that of the unpulsed component. The total 2-10 keV flux of the pulsar is $1.7 \times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$. These results confirm PSR J1930+1852 as a typical Crab-like pulsar.

Discovery of two candidate pulsar wind nebulae in very-high-energy gamma rays

We present the discovery of two very-high-energy gamma-ray sources in an ongoing systematic search for emission above 100 GeV from pulsar wind nebulae in survey data from the H.E.S.S. telescope array. Imaging Atmospheric Cherenkov Telescopes are ideal tools for searching for extended emission from pulsar wind nebulae in the very-high-energy regime. H.E.S.S., with its large field of view of 5 degrees and high sensitivity, gives new prospects for the search for these objects. An ongoing systematic search for very-high-energy emission from energetic pulsars over the region of the Galactic plane between -60 degrees < l < 30 degrees, -2 degrees < b < 2 degrees is performed. For the resulting candidates, the standard H.E.S.S. analysis was applied and a search for multi-wavelength counterparts was performed. We present the discovery of two new candidate gamma-ray pulsar wind nebulae, HESS J1718-385 and HESS J1809-193. H.E.S.S. has proven to be a suitable instrument for pulsar wind nebula searches.

The Chandra View of the Supernova Remnant 0506-68.0 in the Large Magellanic Cloud

A new Chandra observation of SNR 0506-68.0 (also called N23) reveals a complex, highly structured morphology in the low energy X-ray band and an isolated compact central object in the high energy band. Spectral analysis indicates that the X-ray emission overall is dominated by thermal gas whose composition is consistent with swept-up ambient material. There is a strong gradient in ambient density across the diameter of the remnant. Toward the southeast, near a prominent star cluster, the emitting density is 10 - 23 cm^{-3} while toward the northwest it has dropped to a value of only 1 cm^{-3}. The total extent of the X-ray remnant is 100" by 120" (24 pc x 29 pc for a distance of 50 kpc), somewhat larger than previously known. The remnant's age is estimated to be ~4600 yr. One part of the remnant shows evidence for enhanced O, Ne, and perhaps Mg abundances, which is interpreted as evidence for ejecta from a massive star core collapse supernova. The compact central object has a luminosity of a few times 10^{33} ergs/s and no obvious radio or optical counterpart. It does not show an extended nebula or pulsed emission as expected from a young energetic pulsar, but resembles the compact central objects seen in other core collapse SNe, such as Cas A.

A Near‐Infrared Search for Counterparts to Three Pulsars in Young Supernova Remnants

We present moderately deep JHKs-band searches for near-infrared counterparts to three energetic pulsars in young supernova remnants: PSR B1509-58, PSR J1811-1925, and PSR J1930+1852. We identify a possible counterpart to PSR B1509-58 (which has H 20.6 mag and Ks 19.4 mag, comparable to the flux extrapolated from the X-ray spectrum) with an X-ray-to-infrared flux ratio very similar to that of the Crab pulsar on the basis of its coincidence with the X-ray and radio positions and its anomalous colors, but whether or not we have identified the correct counterpart remains to be confirmed by future observations. For PSR J1811-1925 and PSR J1930+1852 we detect no counterparts, which seems to be consistent with the X-ray-to-infrared flux ratios implied by other young pulsars.

High-frequency observations of southern pulsars

We present polarization data for 32 mainly southern pulsars at 8.4 GHz. The observations show that the polarization fraction is low in most pulsars at this frequency except for the young, energetic pulsars which continue to show polarization fractions in excess of 60 per cent. All the pulsars in the sample show evidence for conal emission with only one third also showing core emission. Many profiles are asymmetric, with either the leading or the trailing part of cone not detectable. Somewhat surprisingly, the asymmetric profiles tend to be more polarized than the symmetrical profiles. Little or no pulse narrowing is seen between 1 and 8.4 GHz. The spectral behaviour of the orthogonal polarization modes and radius to frequency mapping can likely account for much of the observational phenomenology. Highly polarized components may orginate from higher in the magnetosphere than unpolarized components.

Radio Ejection and Bump‐related Orbital Period Gap of Millisecond Binary Pulsars

The monotonic increase of the radius of low mass stars during their ascent on the red giant branch halts when they suffer a temporary contraction. This occurs when the hydrogen burning shell reaches the discontinuity in hydrogen content left from the maximum increase in the convective extension, at the time of the first dredge up, and produces a well known in the luminosity function of the red giants of globular clusters. If the giant is the mass losing component in a binary in which mass transfer occurs on the nuclear evolution time scale, this event produces a temporary stop in the mass transfer, which we will name bump related detachment. If the accreting companion is a neutron star, in which the previous mass transfer has spun up the pulsar down to millisecond periods, the subsequent mass transfer phase may be altered by the presence of the energetic pulsar. In fact, the onset of a radio--ejection phase produces loss of mass and angular momentum from the sytem. We show that this sequence of events may be at the basis of the shortage of systems with periods between ~ 20 and 60 days in the distribution of binaries containing millisecond pulsars. We predict that systems which can be discovered at periods into the gap should have preferentially either magnetic moments smaller than ~ 2 x10^{26}Gcm^3, or larger than ~ 4x10^{26}Gcm^3. We further show that this period gap should not be present in population II.