Vela-like Pulsars Research Articles

Glitches due to quasineutron-vortex scattering in the superfluid inner crust of a pulsar

We revisit the mechanism of vortex unpinning caused by the neutron-vortex scattering \cite{prad1} in the inner crust of a pulsar. The strain energy released by the crustquake is assumed to be absorbed in some part of the inner crust and causes pair-breaking quasi-neutron excitations from the existing free neutron superfluid in the bulk of the inner crust. The scattering of these quasi-neutrons with the vortex core normal neutrons unpins a large number of vortices from the thermally affected regions and results in pulsar glitches. We consider the geometry of a cylindrical shell of the affected pinning region to study the implications of the vortex unpinning in the context of pulsar glitches. We find that a pulsar can release about $\sim 10^{11} - 10^{13}$ vortices by this mechanism. These numbers are equivalent to the glitch size of orders $\sim 10^{-11} - 10^{-9}$ for Vela-like pulsars with the characteristic age $\tau \simeq 10^4$ years. We also suggest a possibility of a vortex avalanche triggered by the movement of the unpinned vortices. A rough estimate of the glitch size caused by an avalanche shows an encouraging result.

Glitches in four gamma-ray pulsars and inferences on the neutron star structure

ABSTRACT We present timing solutions from the Fermi-LAT observations of gamma-ray pulsars PSR J0835 − 4510 (Vela), PSR J1023−5746, PSR J2111+4606, and PSR J2229+6114. Data ranges for each pulsar extend over a decade. From data analysis, we have identified a total of 20 glitches, 11 of which are new discoveries. Among them, 15 glitches are large ones with Δν/ν ≳ 10−6. PSR J1023−5746 is the most active pulsar with glitch activity parameter being Ag = 14.5 × 10−7 yr−1 in the considered data span and should be a target for frequently glitching Vela-like pulsars in future observations. We have done fits within the framework of the vortex creep model for 16 glitches with Δν/ν ≳ 10−7. By theoretical analysis of these glitches, we are able to obtain important information on the structure of neutron star, including moments of inertia of the superfluid regions participated in glitches and coupling time-scales between various stellar components. The theoretical prediction for the time to the next glitch from the parameters of the previous one is found to be in qualitative agreement with the observed inter-glitch time-scales for the considered sample. Recoupling time-scales of the crustal superfluid are within the range of theoretical expectations and scale inversely with the spin-down rate of a pulsar. We also determined a braking index n = 2.63(30) for PSR J2229+6114 after glitch-induced contributions have been removed.

Classification of Young Pulsars and Empirical Evolution of Regular Braking Index

Abstract—The distribution of young pulsars in the log(dP/dt)–log(tc) diagram that have a characteristic age tc ~10–16 is analyzed. Six clusters-stripes are revealed for the first time, along which the long-term evolution tracks of individual pulsars pass. The mean track in a stripe corresponds to the long-term regular evolution for a typical pulsar of this stripe. The clusters-stripes population composition is analyzed by object types. Rotating radio transients (RRATs) are present in all clusters-stripes at tc > 105 yr. It turns out that three stripes contain objects of only one of the three numerous (≥10) known types: magnetars, pulsars with a high magnetic field, and Vela-like pulsars. In three other clusters-stripes, objects of the indicated three types are not found. The following object classification in the composition of six clusters-stripes is proposed: magnetars (M), pulsars with a high magnetic field (HB), pulsars with a sub-high magnetic field (S-HB), Vela-type pulsars (V), sub-Vela pulsars (SV), and low magnetic field pulsars (LB). Four pulsars that are outside the stripes are referred to peculiar. Analytical formulas are presented for calculating evolution parameters in the log(dP/dt)–log(tc) diagram. As a result of the optimal fitting of the mean clusters-stripes track by the appropriate empirical function, long-term regular values of the braking index and the second derivative of the period are estimated for 327 pulsars for the first time. As a consequence of the clusters-stripes presence, the “striped” distribution of the dipole magnetic field at pulsar birth indicates the intervality in the mass distribution of pulsar progenitor stars. The recent supernovae explosion models (Pejcha & Thomson, 2015) also produce an interval mass distribution of progenitors generating neutron stars, which confirm that pulsar clusters-stripes do exist and their origin can be naturally explained.

Glitches: The Exact Quantum Signatures of Pulsars Metamorphosis

The observed recurrence of glitches in pulsars and neutron stars carry rich information about the evolution of their internal structures. In this article I show that the glitch-events observed in pulsars are exact quantum signatures for their metamorphosis into dark super-baryons (SBs), whose interiors are made of purely incompressible superconducting gluon-quark superfluids. Here the quantum nuclear shell model is adopted to describe the permitted energy levels of the SB, which are assumed to be identical to the discrete spinning rates $\Omega_{SB},$ that SBs are allowed to rotate with. Accordingly, a glitch-event corresponds to a prompt spin-down of the superconducting SB from one energy level to the next, thereby expelling a certain number of vortices, which in turn spins-up the ambient medium. The process is provoked mainly by the negative torque of the ambient dissipative nuclear fluid and by a universal scalar field $\phi$ at the background of a supranuclear dense matter. As dictated by the Onsager-Feynman equation, the prompt spin-down must be associated with increase of the dimensions of the embryonic SB to finally convert the entire pulsar into SB-Objects on the scale of Gyrs. Based on our calculations, a Vela-like pulsar should display billions of glitches during its lifetime, before it metamorphoses entirely into a maximally compact SB-object and disappears from our observational windows. The present model predicts the mass of SBs and $\Delta \Omega/\Omega$ in young pulsars to be relatively lower than their older counterparts.

Rotating NSs/QSs and recent astrophysical observations

Both fast and slow configurations of rotating neutron stars (NSs) are studied with the recently-constructed unified NS EoSs. The calculations for pure quark stars (QSs) and hybrid stars (HSs) are also done, using several updated quark matter EoSs and Gibbs construction for obtaining hadron-quark mixed phase. All three types of EoSs fulfill the recent 2-solar-mass constraint. By confronting the glitch observations with the theoretical calculations for the crustal moment of inertia (MoI), we find that the glitch crisis is still present in Vela-like pulsars. An upcoming accurate MoI measurement (eg., a possible 10% accuracy for pulsar PSR J0737–3039A) allows one to distinguish QSs from NSs, since the MoIs of QSs are generally ≳ 1.5 times larger than NSs and HSs, no matter the compactness and the mass of the stars. Using tabulated EoSs, we compute stationary and equilibrium sequences of rapidly rotating, relativistic stars in general relativity from the well-tested rns code, assuming the matter comprising the star to be a perfect fluid. All three observed properties of the short gamma-ray bursts (SGRBs) internal plateaus sample are simulated using the rotating configurations of NSs/QSs as basic inputs. We finally argue that for some characteristic SGRBs, the post-merger products of NS-NS mergers are probably supramassive QSs rather than NSs, and NS-NS mergers are a plausible location for quark deconfinement and the formation of QSs.

New long-term braking index measurements for glitching pulsars using a glitch-template method

Braking index measurements offer the opportunity to explore the processes affecting the long-term spin evolution of pulsars and possible evolutionary connections between the various pulsar populations. For young pulsars the long-term trends are generally obscured by short term phenomena such as timing noise and the recoveries form large glitches. Here we present a new method to overcome the latter and report on braking index measurements for the Vela-like pulsars PSR B1800-21 and PSR B1823-13, an updated measurement for Vela and new estimates for four more glitching pulsars observed at Jodrell Bank Observatory. The values of braking indices describe the long-term evolution of the pulsars across the P-P' diagram. Despite some measurements being affected by considerable uncertainties, there is evidence for a common trend involving low braking indices (n<=2) among young glitching pulsars. Such values introduce a new variant in the evolution of young pulsars and their relationship with other populations in the P-P' diagram. Low braking indices also imply that these pulsars could be a few times older than their characteristic ages. We consider PSR B1757-24 and conclude that the pulsar could be old enough to be related to the supernova remnant G5.4-1.2. Between glitches, the short-term evolution of Vela-like pulsars is characterised by large inter-glitch braking indices n_ig > 10. We interpret both short and long term trends as signatures of the large glitch activity, and speculate that they are driven by short-term post-glitch re-coupling and a cumulative long-term decoupling of superfluid to the rotation of the star.

Deep optical imaging of theγ-ray pulsar J1048–5832 with the VLT

(abridged) PSR J1048-5832 is a young Vela-like pulsar that was recently detected in gamma-rays with Fermi, and also in X-rays with Chandra and XMM-Newton. It powers a compact PWN visible in X-rays. We present deep optical observations with the ESO Very Large Telescope to search for optical counterparts of the pulsar and its nebula and to explore their multi-wavelength emission properties. The data were obtained in V and R bands and compared with archival data in other spectral domains. We do not detect the pulsar in the optical and derive informative upper limits of R > 28.1 mag and V > 28.4 mag for its brightness. Using a red-clump star method, we estimate an interstellar extinction towards the pulsar of 2 mag, which is consistent with the absorbing column density derived form X-rays. The respective distance agrees with the dispersion measure distance. We reanalyse the Chandra X-ray data and compare the dereddened upper limits with the unabsorbed X-ray spectrum of the pulsar. We find that regarding its optical-X-ray spectral properties this gamma-ray pulsar is not distinct from other pulsars detected in both ranges. However, like the Vela pulsar, it is very inefficient in the optical and X-rays. Among a dozen optical sources overlapping with the pulsar X-ray nebula we find one with V = 26.9 and R = 26.3 mag, whose colour is slightly bluer then that of the field stars and consistent with the peculiar colours typical for pulsar nebula features. It positionally coincides with a relatively bright feature of the pulsar X-ray nebula, resembling the Crab wisp and locating in 2 arcsec from the pulsar. We suggest this source as a counterpart candidate to the feature. Based on the substantial interstellar extinction towards the pulsar and its optical inefficiency, further optical studies should be carried out at longer wavelengths.

Deep optical observations of the γ-ray pulsar PSR J0007+7303 in the CTA 1 supernova remnant

The Fermi Large Area Telescope (LAT) discovered the time signature of a radio-silent pulsar coincident with RX J0007.0+7302, a plerion-like X-ray source at the centre of the CTA 1 supernova remnant. The inferred timing parameters of the gamma-ray pulsar PSR J0007+7303 (P=315.8 ms; dot{P}\sim3.6 10^{-13} s s^{-1}) point to a Vela-like neutron star, with an age comparable to that of CTA 1. The PSR J0007+7303 low distance (\sim 1.4 kpc), interstellar absorption (A_V\sim 1.6), and relatively high energy loss rate (dot{E} \sim4.5 10^{35} erg s^{-1}), make it a suitable candidate for an optical follow-up. Here, we present deep optical observations of PSR J0007+7303. The pulsar is not detected in the Gran Telescopio Canarias (GTC) images down to a limit of r'\sim 27.6 (3 sigma), the deepest ever obtained for this pulsar, while William Herschel Telescope (WHT) images yield a limit of V \sim 26.9. Our r'-band limit corresponds to an optical emission efficiency \eta_{opt}= L_{opt}/dot{E} < 9.4 10^{-8}. This limit is more constraining than those derived for other Vela-like pulsars, but is still above the measured optical efficiency of the Vela pulsar. We compared the optical upper limits with the extrapolation of the XMM-Newton X-ray spectrum and found that the optical emission is compatible with the extrapolation of the X-ray power-law component, at variance with what is observed, e.g. in the Vela pulsar.

A study of 315 glitches in the rotation of 102 pulsars

The rotation of more than 700 pulsars has been monitored using the 76-m Lovell Telescope at Jodrell Bank. Here we report on a new search for glitches in the observations, revealing 128 new glitches in the rotation of 63 pulsars. Combining these new data with those already published we present a database containing 315 glitches in 102 pulsars. The database was used to study the glitch activity among the pulsar population, finding that it peaks for pulsars with a characteristic age tau_c ~ 10kyr and decreases for longer values of tau_c, disappearing for objects with tau_c > 20Myr. The glitch activity is also smaller in the very young pulsars (tau_c <~ 1kyr). The cumulative effect of glitches, a collection of instantaneous spin up events, acts to reduce the regular long term spindown rate |nudot| of the star. The percentage of |nudot| reversed by glitch activity was found to vary between 0.5% and 1.6% for pulsars with spindown rates |nudot| between 10^(-14) and 3.2*10^(-11) Hz/s, decreasing to less than 0.01% at both higher and lower spindown rates. These ratios are interpreted in terms of the amount of superfluid involved in the generation of glitches. In this context the activity of the youngest pulsar studied, the Crab pulsar, may be explained by quake-like activity within the crust. Pulsars with low spindown rates seem to exhibit mostly small glitches, matching well the decrease of their crustal superfluid. Through the analysis of glitch sizes it was found that the particular glitching behaviour of PSR J0537-6910 and the Vela pulsar may be shared by most Vela-like pulsars. These objects present most of their glitches with characteristic frequency and frequency derivative jumps, occurring at regular intervals of time. Their behaviour is different from other glitching pulsars of similar characteristic age.

DISCOVERY OF NEW GAMMA-RAY PULSARS WITH AGILE

Using gamma-ray data collected by the Astro-rivelatore Gamma ad Immagini LEggero (AGILE) satellite over a period of almost one year (from 2007 July to 2008 June), we searched for pulsed signals from 35 potentially interesting radio pulsars, ordered according to and for which contemporary or recent radio data were available. AGILE detected three new top-ranking nearby and Vela-like pulsars with good confidence both through timing and spatial analysis. Among the newcomers we find pulsars with very high rotational energy losses, such as the remarkable PSR B1509 − 58 with a magnetic field in excess of 1013 Gauss, and PSR J2229 + 6114 providing a reliable identification for the previously unidentified EGRET source 3EG 2227 + 6122. Moreover, the powerful millisecond pulsar B1821 − 24, in the globular cluster M28, is detected during a fraction of the observations. Four other promising gamma-ray pulsar candidates, among which is the notable J2043 + 2740 with an age in excess of 1 million years, show a possible detection in the timing analysis only and deserve confirmation.

High‐Energy Phase‐Averaged Spectra from Gamma‐Ray Pulsars

We study high-energy radiation properties based on the vacuum outer gap model given by Zhang et al. In this model, the outer gap is sustained by a sufficient number of electron/positron pairs which are created through X-ray and high-energy photon interactions, forming a self-consistent outer gap. For a pulsar with known parameters such as period P, surface magnetic field Bp, and magnetic inclination angle α, the geometry of the outer gap (i.e., the transfield height and the radii of inner and outer boundaries of the outer gap) can be determined, and the radiation inside the outer gap along the kth field line which is tangent to the cylinder with a radius of R'L = kBRL is treated as a typical high-energy radiation, where RL = cP/2π is the light cylinder radius and kB is a parameter. We describe the calculation method of the γ-ray spectrum for a given γ-ray pulsar, calculate high-energy spectra for five known γ-ray pulsars (i.e., Geminga-like pulsars: Geminga and PSR B1055–52, and Vela-like pulsars: Vela, PSR B1951+32 and PSR B1706–44), and compare them with the observed data.

Hydrostatic equilibrium of causally consistent and dynamically stable neutron star models

We show that the mass-radius $(M-R)$ relation corresponding to the stiffest equation of state (EOS) does not provide the necessary and sufficient condition of dynamical stability for the equilibrium configurations, since such configurations can not satisfy the `compatibility criterion'. In this connection, we construct sequences composed of core-envelope models such that, like the stiffest EOS, each member of these sequences satisfy the extreme case of causality condition, $v = c = 1$, at the centre. We, thereafter, show that the $M-R$ relation corresponding to the said core-envelope model sequences can provide the necessary and sufficient condition of dynamical stability only when the `compatibility criterion' for these sequences is `appropriately' satisfied. However, the fulfillment of `compatibility criterion' can remain satisfied even when the $M-R$ relation does not provide the necessary and sufficient condition of dynamical stability for the equilibrium configurations. In continuation to the results of previous study, these results explicitly show that the `compatibility criterion' {\em independently} provides, in general, the {\em necessary} and {\em sufficient} condition of hydrostatic equilibrium for any regular sequence. Beside its fundamental feature, this study can also explain simultaneously, both (the higher as well as lower) values of the glitch healing parameter observed for the Crab and the Vela-like pulsars respectively, on the basis of starquake model of glitch generation.

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.

ChandraDetection of a Synchrotron Nebula around the Vela‐like Pulsar J1016−5857

We report on a 19 ks observation of the pulsar J1016-5857 with the Chandra X-Ray Observatory. This Vela-like pulsar has rotation period 107 ms, characteristic age 21 kyr, and spin-down power 2.6 × 1036 ergs s-1. A relatively bright, centrally peaked source of radius ≈25'' around the radio pulsar position has a spectrum that is well fitted by an absorbed power law with photon index 1.32 ± 0.25. We regard this as a newly identified pulsar wind nebula (PWN) that we designate PWN G284.0-1.8. We do not detect the pulsar as either a point X-ray source or a pulsed source in a 55 ks observation with the Rossi X-Ray Timing Explorer. The isotropic PWN luminosity is 3 × 1032 ergs s-1 in the 2-10 keV range, for a distance of 3 kpc that is consistent with the measured neutral hydrogen column density. The unpulsed flux from the pulsar is less than 30% of the measured PWN flux. The brightest component of the PWN, near the pulsar, shows extended emission of size ~2'' that may indicate, by analogy with other young pulsars, the wind termination shock. In the Chandra image we also detect a very faint extended structure ≈1' × 2' in size that is highly asymmetric about the pulsar position. This structure is a good match in width and position angle to the tip of a finger of radio emission that appears to connect to the nearby supernova remnant G284.3-1.8, but we cannot characterize it further with the available data. There is a variable X-ray point source only 15 from the pulsar, which we identify using optical spectroscopy as an accreting binary.

A search for giant pulses in Vela-like pulsars

We have carried out a survey for ‘giant pulses’ in six young, Vela-like pulsars. In no cases did we find single pulses with flux densities more than 10 times the mean flux density. However, in PSR B1706–44 we have detected giant micro-pulses very similar to those seen in the Vela pulsar. In PSR B1706–44 these giant micro-pulses appear on the trailing edge of the profile and have an intrinsic width of ∼1 ms. The cumulative probability distribution of their intensities is best described by a power law. If the power law continues to higher intensities, then 3.7×106 rotations are required to obtain a pulse with 20× the mean pulse flux. This number is similar to the giant pulse rate in PSR B1937+21 and PSR B1821–24 but significantly higher than that for the Crab.

Radiation from Vela-like pulsars near the death line

Radiation of both the outer gaps and the neutron star surface is considered for a Vela-like pulsar near the death line. It is shown that if such a pulsar is close enough to the death line, its optical, UV and X-ray emission has to increase. Using results of this consideration, it is argued that Geminga is not a close relative of Vela-like pulsars. The outer gap model of Geminga in which the main part of the outer gap volume operates as a Vela-like generator of $\gamma$-rays is ruled out. A Vela-like mechanism of $\gamma$-ray generation can operate only in a small region of the outer gap of Geminga. The length of this region along the magnetic field is an order of magnitude smaller than the outer gap dimensions. In the magnetosphere of Geminga the main mechanism of $\gamma$-ray generation at $\sim 10 - 10^4$ MeV is curvature radiation and not the synchrotron radiation as it was assumed for Vela-like pulsars.

Very high energy gamma rays from millisecond pulsars

In this paper we concentrate on the emission of TeV γ - rays from radio pulsars. It will be shown that the polar gap model fails to explain the observed TeV flux levels: The X-ray luminosity should exceed the TeV luminosity if the latter originates from the polar gap regions. The outer gap model of Cheng, Ho and Ruderman provides a consistent picture of TeV γ - ray emission: The total gap power is converted to TeV γ - rays by means of the inverse Compton scattering of primary electrons on the abundant soft IR flux in and around the gap. A fraction exp(−f − 1 2 ) escapes photon-photon absorption and may be observable Here f (∼ 0.1 for Vela and Vela-like pulsars) is the fraction of the open magnetosphere occupied by the gap. The remaining power is used for the gap sustaining mechanism. As the pulsar grows older, f → 1 and the TeV power increases and becomes comparable to the spindown power. This is the so-called “post Vela-like” stage. The model is applied to millisecond pulsars which are all Vela- and post Vela-like. The luminosity estimates are consistent with the TeV observations - despite the experimental uncertainties and theoretical assumptions.

Evolution of a short-period gamma-ray pulsar family - Crab, Vela. COS B source, gamma-ray burst source

view Abstract Citations (96) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evolution of a Short-Period Gamma-Ray Pulsar Family: Crab, Vela, COS B Source, Gamma-Ray Burst Source Ruderman, M. ; Cheng, K. S. Abstract The effects of spinning down are followed in a model for certain families of short-period solitary gamma-ray pulsars. The model pulsars evolve through phases in which they successively resemble the Crab pulsar, Vela, and 'unidentified' COS B source, a Geminga-like object, and a transient gamma-ray burst (GRB) source. The behavior of the star at each stage is discussed. The model ultimately results in a large Galactic population of aligned latent Vela-like pulsars with periods of 0.1-0.2 sec. If temporarily reignited by appropriate 'matches' such as small, infrequent pulsar cap X-ray bursts from weak accretion of interstellar matter, these latent, rapidly spinning pulsars could radiate with the intensity and spectrum of most hard-spectrum GRB sources. Publication: The Astrophysical Journal Pub Date: December 1988 DOI: 10.1086/166929 Bibcode: 1988ApJ...335..306R Keywords: Cos-B Satellite; Crab Nebula; Gamma Ray Bursts; Pulsars; Stellar Evolution; Stellar Rotation; Dipole Moments; Magnetic Dipoles; Astrophysics; GAMMA RAYS: BURSTS; PULSARS; STARS: EVOLUTION; STARS: ROTATION full text sources ADS | data products SIMBAD (9)