PSR J2021 Research Articles

The distance of the SNR Kes 75 and PWN PSR J1846-0258 system

The supernova remnant (SNR) Kes 75/PSR J1846-0258 association can be regarded as certain due to the accurate location of young PSR J1846-0258 at the center of Kes 75 and the detected bright radio/X-ray synchrotron nebula surrounding the pulsar. We provide a new distance estimate to the SNR/pulsar system by analyzing the HI and $^{13}$CO maps, the HI emission and absorption spectra, and the $^{13}$CO emission spectrum of Kes 75. No absorption features at negative velocities strongly argue against the widely-used large distance of 19 to 21 kpc for Kes 75, and show that Kes 75 is within the Solar circle, i.e. a distance $d<$13.2 kpc. Kes 75 is likely at distance of 5.1 to 7.5 kpc because the highest HI absorption velocity is at 95 km/s and no absorption is associated with a nearby HI emission peak at 102 km/s in the direction of Kes 75. This distance to Kes 75 gives a reasonable luminosity of PSR J1846-0258 and its PWN, and also leads to a much smaller radius for Kes 75. So the age of the SNR is consistent with the spin-down age of PSR J1846-0258, confirming this pulsar as the second-youngest in the Galaxy.

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.

X‐Ray Emission from PSR J1809−1917 and Its Pulsar Wind Nebula, Possibly Associated with the TeV Gamma‐Ray Source HESS J1809−193

We detected X-ray emission from the 50-kyr-old pulsar J1809‐1917 and resolved its pulsar wind nebula (PWN) with the Chandra X-ray Observatory. The pulsar’s observed flux is Fpsr = (1: 8� 0: 2)� 10 -14 ergs cm -2 s -1 in the 1‐6 keV band. A two-component blackbody+power-law (BB+PL) fit of the pulsar’s spectrum yields the photon index psr = 1: 2� 0: 6 and luminosity L psr = (4� 1)� 10 31 ergs s -1 of the PL component, in the 0.5‐8 keV band, for a plausible distance d = 3: 5 kpc and nH = 0: 7� 10 22 cm -2 . The BB component corresponds to the temperature T � 2 MK, and bolometric luminosity L bol � 1� 10 32 ergs s -1 . The bright inner PWN component of a 3 00 � 12 00 size is elongated in the north-south direction, with the pul sar close to its south end. This component is immersed in a larger (� 20 00 � 40 00 ), similarly elongated outer PWN component of lower surface brightness. The elongated shape of the compact PWN can be explained by the ram pressure confinement of the pulsar wind due to the supersonic motion of the pulsar. The observed flux of the compact PWN, including both components, is Fpwn ’ (1: 5� 0: 1)� 10 -13 ergs cm -2 s -1 in the 1‐6 keV band. The PWN spectrum can be fitted with a PL model with nH � 0: 7� 10 22 cm -2 and photon index pwn = 1: 4� 0: 1, corresponding to the 0.5‐8 keV luminosity Lpwn � 4� 10 32 ergs s -1 . The compact PWN appears to be inside a more extended (� 4 0 � 4 0 ) emission with the total observed flux Fext � 5� 10 -13 ergs s -1 in the 0.8‐7 keV band. This large-scale emission is more extended to the south of the pulsar, i.e. in the direction of the alleged pulsar motion. To explain the extended X-ray emission ahead of the moving pulsar, one has to invoke strong intrinsic anisotropy of the pulsar wind or assume that this e mission comes from a relic PWN swept by the asymmetrical reverse SNR shock. The pulsar and its PWN are located within the extent of the unidentified TeV source HESS J1809‐193. The brightest part of the TeV source is offset by � 8 0 to the south of the pulsar, i.e. in the same direction as the large-scale X-ray emission. Altho ugh the association between the PSR J1809‐1917 and HESS J1809‐193 is plausible, an alternative source of relativistic electrons powering HESS J1809‐193 might be the serendipitously discovered X-ray source CXOU J180940.7-192544. In addition to the CMBR or Galactic starlight background, the low-frequency seed p hotons for Compton upscattering to TeV energies might be supplied by bright infrared emission from dust-molecular clouds seen within HESS J1809‐193. Subject headings: pulsars: individual (PSR J1809‐1917) — X-rays: individual (CXOU J180940.7-192544, CXOU 180933.3-192959) — gamma-rays: individual (HESS J1809‐193) — ISM: individual (IRAS 18067‐1927, IRAS 18067‐1921)

INTEGRAL detection of the pulsar wind nebula in PSR J1846–0258

We communicate the detection of soft (20--200 keV) gamma-rays from the pulsar and pulsar wind nebula of PSR J1846-0258 and aim to identify the component of the system which is responsible for the gamma-ray emission. To pinpoint the source of gamma-ray emission we combine spectral information from the INTEGRAL gamma-ray mission with archival data from the Chandra X-ray Observatory. Our analysis shows that the soft gamma-rays detected from PSR J1846-0258 include emission from both the pulsar and the pulsar wind nebula, but the measured spectral shape is dominated by the pulsar wind nebula. We further discuss PSR J1846-0258 in the context of rotation-powered pulsars with high magnetic field strengths and review the anomalously high fraction of spin-down luminosity converted into X- and gamma-ray emission in light of a possible overestimate of the distance to this pulsar.

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.

First X-Ray Observations of the Young Pulsar J1357-6429

The first short Chandra and XMM-Newton observations of the young and energetic pulsar J1357-6429 provided strong indications of a tail-like pulsar-wind nebula associated with this object, as well as pulsations of its X-ray flux with a pulsed fraction above 50% and a thermal component dominating at lower photon energies (below 2 keV). The elongated nebula is very compact in size and may be interpreted as evidence for a pulsar jet. The thermal radiation is most plausibly emitted from the entire neutron star surface of a 10 km radius and a 1.0+/-0.1 K temperature, covered with a magnetized hydrogen atmosphere. At higher energies the pulsar's emission is of a nonthermal (magnetospheric) origin, with a power-law spectrum of a photon index of 1.1-1.3. This makes the X-ray properties of PSR J1357-6429 very similar to those of the youngest pulsars J1119-6127 and Vela with a detected thermal radiation.

VLT/NACOobservations of the high-magnetic field radio pulsar PSR J1119-6127

Context. Recent radio observations have unveiled the existence of a number of radio pulsars with spin-down derived magnetic fields in the magnetar range. However, their observational properties appear to be more similar to those of the classical radio pulsars than to the magnetars’s ones. Aims. To shed light on this puzzle we first have to determine whether the spin-down derived magnetic field values for these radio pulsars are indeed representative of the actual neutron star magnetic field or if they are polluted, e.g. by the effects of a torque from a fallback disk. Methods. To investigate this possibility, we have performed deep IR (J,H,Ks bands) observations of one of these high magnetic field radio pulsars (PSR J1119–6127) with the ESO VLT to search for IR emission which can be associated with a disk. Results. No IR emission is detected from the pulsar position down to J ∼ 24, H ∼ 23 and Ks ∼ 22. Conclusions. By comparing our flux upper limits with the predictions of fallback disk models, we have found that we can only exclude the presence of a disk with accretion rate u M > 3 × 10 16 gs −1 . This lower limit cannot rule out the presence of a substantial disk torque on the pulsar, which would then lead to overestimate the value of the magnetic field inferred from P and u P .W e have also compared the upper limit on the IR luminosity of PSR J1119–6127 with the IR luminosities of rotation-powered pulsars and magnetars. We found that, while magnetars are intrinsically more efficient IR emitters than rotation-powered pulsars, possibly because of their higher magnetic field, the relatively low IR emission efficiency of PSR J1119–6127 suggests that it is more similar to the latters than to the former.

INTEGRAL observations of TeV plerions

Amongst the sources seen in very high gamma-rays several are associated with Pulsar Wind Nebulae (“TeV plerions”). The study of hard X-ray/soft gamma-ray emission is providing an important insight into the energetic particle population present in these objects. The unpulsed emission from pulsar/pulsar wind nebula systems in the energy range accessible to the INTEGRAL satellite is mainly synchrotron emission from energetic and fast cooling electrons close to their acceleration site. Our analyses of public INTEGRAL data of known TeV plerions detected by ground based Cherenkov telescopes indicate a deeper link between these TeV plerions and INTEGRAL detected pulsar wind nebulae. The newly discovered TeV plerion in the northern wing of the Kookaburra region (G313.3+0.6 powered by the middle aged PSR J1420-6048) is found to have a previously unknown INTEGRAL counterpart which is besides the Vela pulsar the only middle aged pulsar detected with INTEGRAL. We do not find an INTEGRAL counterpart of the TeV plerion associated with the X-ray PWN “Rabbit” G313.3+0.1 which is possibly powered by a young pulsar.

Discovery of X-ray emission from the young radio pulsar PSR J1357–6429

We present the first X-ray detection of the very young pulsar PSR J1357-6429 (characteristic age of 7.3 kyr) using data from the XMM-Newton and Chandra satellites. We find that the spectrum is well described by a power-law plus blackbody model, with photon index Gamma=1.4 and blackbody temperature kT=160 eV. For the estimated distance of 2.5 kpc, this corresponds to a 2-10 keV luminosity of about 1.2E+32 erg/s, thus the fraction of the spin-down energy channeled by PSR J1357-6429 into X-ray emission is one of the lowest observed. The Chandra data confirm the positional coincidence with the radio pulsar and allow to set an upper limit of 3E+31 erg/s on the 2-10 keV luminosity of a compact pulsar wind nebula. We do not detect any pulsed emission from the source and determine an upper limit of 30% for the modulation amplitude of the X-ray emission at the radio frequency of the pulsar.

The Origin and Motion of PSR J0538+2817 in S147

We report on VLBA astrometry and CXO imaging of PSR J0538+2817 in the supernova remnant S147. We measure a parallax distance of $1.47^{+0.42}_{-0.27}$kpc along with a high-precision proper motion, giving a transverse velocity $V_\perp=400^{+114}_{-73}$km/s. A small extended wind nebula is detected around the pulsar; the symmetry axis of this structure suggests that the spin axis lies $12\arcdeg\pm4\arcdeg$ from the velocity vector (2-D), but the emission is too faint for robust model independent statements. The neutron star is hot, consistent with the young ~40kyr kinematic age. The pulsar progenitor is likely a runaway from a nearby cluster, with NGC 1960 (M36) a leading candidate.

A Shell of Thermal X‐Ray Emission Surrounding the Young Crab‐like Remnant 3C 58

Deep X-ray imaging spectroscopy of the bright pulsar wind nebula 3C 58 confirms the existence of an embedded thermal X-ray shell surrounding the pulsar PSR J0205+6449. Radially resolved spectra obtained with the XMM-Newton telescope are well characterized by a power-law model with the addition of a soft thermal emission component in varying proportions. These fits reproduce the well-studied increase in the spectral index with radius attributed to synchrotron burn off of high energy electrons. Most interestingly, a radially resolved thermal component is shown to map out a shell-like structure ≈6' in diameter. The presence of a strong emission line corresponding to the Ne IX He-like transition requires an overabundance of ~3 × (Ne/Ne☉) in the Raymond-Smith plasma model. The best-fit temperature kT ~ 0.23 keV is essentially independent of radius for the derived column density of NH = (4.2 ± 0.1) × 1021 cm-2. Our result suggests that thermal shells can be obscured in the early evolution of a supernova remnant by nonthermal pulsar wind nebulae emission; the luminosity of the 3C 58 shell is more than an order of magnitude below the upper limit on a similar shell in the Crab Nebula. We find the shell centroid to be offset from the pulsar location. If this neutron star has a velocity similar to that of the Crab pulsar, we derive an age of 3700 yr and a velocity vector aligned with the long axis of the PWN. The shell parameters and pulsar offset add to the accumulating evidence that 3C 58 is not the remnant of the supernova of CE 1181.

Three-dimensional hydrodynamic simulations of asymmetric pulsar wind bow shocks

We present three-dimensional, nonrelativistic, hydrodynamic simulations of bow shocks in pulsar wind nebulae. The simulations are performed for a range of initial and boundary conditions to quantify the degree of asymmetry produced by latitudinal variations in the momentum flux of the pulsar wind, radiative cooling in the postshock flow, and density gradients in the interstellar medium (ISM). We find that the bow shock is stable even when travelling through a strong ISM gradient. We demonstrate how the shape of the bow shock changes when the pulsar encounters density variations in the ISM. We show that a density wall can account for the peculiar bow shock shapes of the nebulae around PSR J2124-3358 and PSR B0740-28. A wall produces kinks in the shock, whereas a smooth ISM density gradient tilts the shock. We conclude that the anisotropy of the wind momentum flux alone cannot explain the observed bow shock morphologies but it is instead necessary to take into account external effects. We show that the analytic (single layer, thin shell) solution is a good approximation when the momentum flux is anisotropic, fails for a steep ISM density gradient, and ap- proaches the numerical solution for efficient cooling. We provide analytic expressions for the latitudinal dependence of a vacuum-dipole wind and the associated shock shape, and compare the results to a split-monopole wind. We find that we are unable to distinguish between these two wind models purely from the bow shock morphology.

Energy dependent γ-ray morphology in the pulsar wind nebula HESS J1825–137

Aims. We present results from deep $\gamma$-ray observations of the Galactic pulsar wind nebula HESS J1825-137 performed with the HESS array. Methods. Detailed morphological and spatially resolved spectral studies reveal the very high-energy (VHE) $\gamma$-ray aspects of this object with unprecedented precision. Results. We confirm previous results obtained in a survey of the Galactic Plane in 2004. The $\gamma$-ray emission extends asymmetrically to the south and south-west of the energetic pulsar PSR J1826-1334 , that is thought to power the pulsar wind nebula. The differential $\gamma$-ray spectrum of the whole emission region is measured over more than two orders of magnitude, from 270 GeV to 35 TeV, and shows indications for a deviation from a pure power law. Spectra have also been determined for spatially separated regions of HESS J1825-137. The photon indices from a power-law fit in the different regions show a softening of the spectrum with increasing distance from the pulsar and therefore an energy dependent morphology. Conclusions. This is the first time that an energy dependent morphology has been detected in the VHE $\gamma$-ray regime. The VHE $\gamma$-ray emission of HESS J1825-137 is phenomenologically discussed in the scenario where the $\gamma$-rays are produced by VHE electrons via Inverse Compton scattering. The high $\gamma$-ray luminosity of the source cannot be explained on the basis of constant spin-down power of the pulsar and requires higher injection power in past.

A Braking Index for the Young, High Magnetic Field, Rotation‐Powered Pulsar in Kesteven 75

We present the first phase-coherent measurement of a braking index for the young, energetic rotation-powered pulsar PSR J1846-0258. This 324 ms pulsar is located at the center of the supernova remnant Kesteven 75 and has a characteristic age of τc = 723 yr, a spin-down energy of Ė = 8.3 × 1036 ergs s-1, and an inferred magnetic field of 4.9 × 1013 G. Two independent phase-coherent timing solutions are derived, which together span 5.5 yr of data obtained with the Rossi X-Ray Timing Explorer. In addition, a partially phase-coherent timing analysis confirms the fully phase-coherent result. The measured value of the braking index, n = 2.65 ± 0.01, is significantly less than 3, the value expected from magnetic dipole radiation, implying another physical process must contribute to the pulsar's rotational evolution. Assuming the braking index has been constant since birth, we place an upper limit on the spin-down age of PSR J1846-0258 of 884 yr, the smallest age estimate of any rotation-powered pulsar.

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.

Green Bank Telescope Studies of Giant Pulses from Millisecond Pulsars

We have conducted a search for giant pulses from four millisecond pulsars using the 100m Green Bank Telescope. Coherently dedispersed time-series from PSR J0218+4232 were found to contain giant pulses of very short intrinsic duration whose energies follow power-law statistics. The giant pulses are in phase with the two minima of the radio integrated pulse profile but are phase aligned with the peaks of the X-ray profile. Historically, individual pulses more than 10-20 times the mean pulse energy have been deemed to be ``giant pulses''. As only 4 of the 155 pulses had energies greater than 10 times the mean pulse-energy, we argue the emission mechanism responsible for giant pulses should instead be defined through: (a) intrinsic timescales of microsecond or nanosecond duration; (b) power-law energy statistics; and (c) emission occurring in narrow phase-windows coincident with the phase windows of non-thermal X-ray emission. Four short-duration pulses with giant-pulse characteristics were also observed from PSR B1957+20. As the inferred magnetic fields at the light cylinders of the millisecond pulsars that emit giant pulses are all very high, this parameter has previously been considered to be an indicator of giant pulse emissivity. However, the frequency of giant pulse emission from PSR~B1957+20 is significantly lower than for other millisecond pulsars that have similar magnetic fields at their light cylinders. This suggests that the inferred magnetic field at the light cylinder is a poor indicator of the rate of emission of giant pulses.

Pulsar Wind Nebulae and the Nonthermal X‐Ray Emission of Millisecond Pulsars

The nonthermal, nonpulsed X-ray emission of MSPs is investigated. As in young pulsars, MSPs emit a relativistic wind, which in interacting with the ISM and/or a binary companion can significantly contribute to the nonpulsed emission of these pulsars. An application and extension of a simple model developed for young pulsars is applied to the old recycled MSP B1957+20. It is found that the pulsar wind can indeed contribute to both the resolved and unresolved X-ray emission. For other MSPs in the Galactic field for which the spectral index of the nonpulsed component has been measured (i.e., PSR B1937+21, PSR J0218+4232) the contribution of the pulsar wind to the nonpulsed X-ray luminosity is estimated. For the MSPs in the core regions of globular clusters, the pulsar wind nebula is likely affected by its interaction with the dense stellar environment, possibly leading to a diminished contribution to the total X-ray emission. In this case, the existence of nonthermal nonpulsed X-ray emission is more likely for binary than for isolated MSPs, with the emission arising from the interaction of the relativistic pulsar wind and a binary companion. Our study suggests that the magnetization parameter in the pulsar wind nebulae of MSPs is significantly larger than that of the Crab Nebula, by about a factor of 10. The nebulae powered by rapidly rotating neutron stars either in isolation or in the quiescent state of soft X-ray transients can contribute to the faint X-ray source population associated with nonaccreting neutron stars. The emission from MSPs moving at high velocities (100 km s-1) through regions of the ISM characterized by magnetic field strengths 0.1 mG may appear spatially extended with a tail-like morphology. Thus, MSPs may also contribute to the faint filamentary X-ray source subpopulation in the Galaxy.

Searches for diffuse X-ray emission around millisecond pulsars: an X-ray nebula associated with PSR J2124-3358

We report on diffuse X-ray emission associated with the nearby solitary millisecond pulsar PSR J2124-3358 detected with XMM-Newton and Chandra. The emission extends from the pulsar to the northwest by ~0.5 arcmin. The spectrum of the nebular emission can be modeled with a power-law of photon index $2.2\pm0.4$, in line with the emission originating from accelerated particles in the post shock flow. For PSR J0437-4715, PSR J0030+0451 and PSR J1024-0719, which all have spin parameters comparable to that of PSR J2124-3358, no diffuse emission is detected down to a 3-sigma limiting flux of $4-7\times10^{-15}$ ergs s$^{-1}$ cm$^{-2}$.

PSR J1833−1034: Discovery of the Central Young Pulsar in the Supernova Remnant G21.5–0.9

We have discovered the pulsar associated with the supernova remnant G21.5-0.9. PSR J1833-1034, with spin period P = 61.8 ms and dispersion measure 169 pc/cc, is very faint, with pulse-averaged flux density of approximately 70 microJy at a frequency of 1.4 GHz, and was first detected in a deep search with the Parkes telescope. Subsequent observations with Parkes and the Green Bank Telescope have confirmed this detection, and yield a period derivative dP/dt = 2.02e-13. These spin parameters imply a characteristic age tau_c = 4.8 kyr and a spin-down luminosity dE/dt = 3.3e37 ergs/s, the latter value exceeded only by the Crab pulsar among the rotation-powered pulsars known in our Galaxy. The pulsar has an unusually steep radio spectrum in the 0.8-2.0 GHz range, with power law index ~3.0, and a narrow single-peaked pulse profile with full-width at half maximum of 0.04P. We have analyzed 350 ks of archival Chandra X-ray Observatory High Resolution Camera (HRC) data, and find a point-like source of luminosity approximately 3e-5dE/dt, offset from the center of an elliptical region of size ~7"x5" and luminosity approximately 1e-3dE/dt within which likely lies the pulsar wind termination shock. We have searched for X-ray pulsations in a 30 ks HRC observation without success, deriving a pulsed fraction upper limit for a sinusoidal pulse shape of about 70% of the pulsar flux. We revisit the distance to G21.5-0.9 based on HI and CO observations, arguing that it is 4.7+-0.4 kpc. We use existing X-ray and radio observations of the pulsar wind nebula, along with the measured properties of its engine and a recent detection of the supernova remnant shell, to argue that G21.5-0.9 and PSR J1833-1034 are much younger than tau_c, and likely their true age is ~<1000 yr. In that case, the initial spin period of the pulsar was >~55 ms.

Tachyonic cyclotron radiation

We study superluminal cyclotron emission by electrons and muons in semiclassical orbits. The tachyonic line spectra of hydrogenic ions such as $\mbox{H}$ , ${}^{56}\mbox{Fe}^{25 + }$ , and ${}^{238} \mbox{U}^{91 + }$ , as well as their muonic counterparts ${p}\mu^-$ , ${}^{56}\mbox{Fe}^{26 + }\mu ^-$ and ${}^{238} \mbox{U}^{92 + }\mu^-$ are calculated, in particular the tachyonic power transversally and longitudinally radiated, the total intensity, and the power radiated in the individual harmonics. We also investigate tachyonic continuum radiation from electrons and protons cycling in the surface and light cylinder fields of $\gamma$ -ray and millisecond pulsars, such as the Crab pulsar, PSR B1509-58, and PSR J0218 + 4232. The superluminal spectral densities generated by non-relativistic, mildly relativistic and ultra-relativistic source particles are derived. We study the parameters determining the global shape of the transversal and longitudinal densities and the energy scales of the broadband spectrum. The observed cutoff frequency in the $\gamma$ -ray band of the pulsars is used to infer the upper edge of the orbital energy, and we conclude that electrons and nuclei cycling in the surface fields can reach energies beyond the "ankle" of the cosmic ray spectrum. This suggests $\gamma$ -ray pulsars as sources of ultra-high energy cosmic rays.