Gamma-ray Pulsars Research Articles

A stacking survey of gamma-ray pulsars

ABSTRACT We report on a likelihood-stacking search for γ-ray pulsars at 362 high-latitude locations that coincide with known radio pulsar positions. We observe a stacked signal conservatively 2.5σ over the background. Stacking their likelihood profiles in spectral parameter space implies a pulsar-like spectral index and a characteristic flux a factor of 2 below the Fermi Large Area Telescope point-source sensitivity, assuming isotropic/unbeamed emission from all sample pulsars. The same procedures performed on empty control fields indicate that the pulsars as a population can be distinguished from the background with a Δ(TS) = 28, where TS refers to test statistic, at the peak location (or 4.8σ), and the stacked spectra of the control fields are distinctly softer than those of the pulsars. This study also probes a unique region of parameter space populated by low $\dot{E}$ pulsars, most of which have no γ-ray ephemeris available, and is sensitive to high duty cycles. We also discuss the possible γ-ray emission mechanism from such pulsars.

Temporal and Spectral Evolution of Gamma-Ray Burst Broad Pulses: Identification of High-latitude Emission in the Prompt Emission

We perform a detailed analysis of broad pulses in bright gamma-ray bursts (GRBs) to understand the evolution of GRB broad pulses. Using the temporal and spectral properties, we test the high-latitude emission (HLE) scenario in the decaying phase of broad pulses. The HLE originates from the curvature effect of a relativistic spherical jet, where higher-latitude photons are delayed and softer than the observer’s line-of-sight emission. The signature of HLE has not yet been identified undisputedly during the prompt emission of GRBs. The HLE theory predicts a specific relation, ∝ , between the peak energy E p in ν F ν spectra and the spectral flux F ν measured at E p , . We search for evidence of this relation in 2157 GRBs detected by the Gamma-ray Burst Monitor on board the Fermi Gamma-ray Space Telescope from 2008 to 2017. After imposing unbiased selection criteria in order to minimize contamination in a signal by background and overlaps of pulses, we build a sample of 32 broad pulses in 32 GRBs. We perform a time-resolved spectral analysis on each of these 32 broad pulses and find that the evolution of 18 pulses (56%) is clearly consistent with the HLE relation. For the 18 broad pulses, the exponent δ in the relation of ∝ E p δ is distributed as a Gaussian function with a median and width of 1.99 and 0.34, respectively. This result provides a constraint on the emission radius of GRBs with the HLE signature.

Heterogeneous Quasi-Continuous Spiking Cortical Model for Pulse Shape Discrimination

The present study introduces the heterogeneous quasi-continuous spiking cortical model (HQC-SCM) method as a novel approach for neutron and gamma-ray pulse shape discrimination. The method utilizes specific neural responses to extract features in the falling edge and delayed fluorescence parts of radiation pulse signals. In addition, the study investigates the contributions of HQC-SCM’s parameters to its discrimination performance, leading to the development of an automatic parameter selection strategy. As HQC-SCM is a chaotic system, a genetic algorithm-based parameter optimization method was proposed to locate local optima of HQC-SCM’s parameter solutions efficiently and robustly in just a few iterations of evolution. The experimental results of this study demonstrate that the HQC-SCM method outperforms traditional and state-of-the-art pulse shape discrimination algorithms, including falling edge percentage slope, zero crossing, charge comparison, frequency gradient analysis, pulse-coupled neural network, and ladder gradient methods. The outstanding discrimination performance of HQC-SCM enables plastic scintillators to compete with liquid and crystal scintillators’ neutron and gamma-ray pulse shape discrimination ability. Additionally, the HQC-SCM method outperforms other methods when dealing with noisy radiation pulse signals. Therefore, it is an effective and robust approach that can be applied in radiation detection systems across various fields.

Novel radionuclides identification method based on Hilbert–Huang Transform and Convolutional Neural Network with gamma-ray pulse signal

Traditional radionuclide identification algorithms are based on gamma-ray spectrum analysis. A novel radionuclide identification method was proposed in this work and it was based on the combined use of the Hilbert–Huang Transform and a Convolutional Neural Network (HHT-CNN) and taken as input data gamma-ray pulses, instead of an entire gamma-ray spectrum. Firstly, HHT was used to analyze the nuclear pulse signal in frequency domain, and then the frequency in the instantaneous-frequency-edge spectrum was divided into multiple intervals, and the accumulation of amplitude in each interval was taken as the characteristic of the nuclear pulse signal. After constructing the data set with signal features, the one-dimensional Convolutional Neural Network (1D-CNN) model was established and trained to complete the nuclide recognition. In the simulated experiments, the model was tested by the nuclear pulse signals of 137Cs, 60Co, 152Eu, 133Ba, 40K, 60Co+137Cs, 60Co+152Eu and 137Cs+152Eu, which were simulated with the Geant4 toolkit and pulse signal simulator DT5800D (produced by CAEN Technologies Inc.). At the same time, the influence of pulse number and noise on the model recognition results was discussed. Finally, the model was applied to the actual experimental data to verify the model’s feasibility further. The results show that the proposed method can quickly and accurately identify radioactive nuclides. The study provides a new solution for radionuclides identification.

Gluon condensation signature in the GeV gamma-ray spectra of pulsars

The accumulation of gluons inside nucleons, i.e., the gluon condensation, may lead to a characteristic broken power-law gamma-ray spectrum in high-energy nucleon collisions. Here we show that the observed spectra of at least 25 sources in the second Fermi Large Area Telescope Catalog of Gamma-ray Pulsars can be well fitted by such a broken power-law function that has only four free parameters. It strongly indicates that the gamma-ray emission from these pulsars is of hadronic origin, but with gluon condensation inside hadrons. It is well known that the quark-gluon distribution in a free nucleon is different from that in a bound nucleon. This work exposes the nuclear $A$ dependence of the gluon condensation effect, where $A$ refers to the baryon number. Our study reveals the gluon condensation under the condition of $A\ensuremath{\rightarrow}\ensuremath{\infty}$, which may open a new window for eavesdropping on the structure of compact stars on the subnuclear level.

Radiation damage on the performance of a silicon photomultiplier-coupled Cs2LiYCl6:Ce3+ detector

A silicon photomultiplier (SiPM) coupled Cs2LiYCl6:Ce3+ (CLYC) detector was developed for neutron detection in the narrow, mixed radiation field. Studies show that the SiPM and scintillator will suffer a certain degree of damage in high-intensity irradiation environments. To evaluate the effects of the radiation damage, the detector was exposed to a zero-power research reactor. The thermal neutron exposures ranged from 0 up to 7.60 × 107 n/cm2. The performance specifications on the gamma ray and thermal neutron pulses, 6Li(n, α)3H thermal neutron peaks, energy resolutions, and pulse shape discrimination were analyzed. The results showed that the standard gamma ray and thermal neutron pulses were slightly altered, the thermal neutron peak centroid reduced by 40%, the energy resolution of the 6Li(n, α)3H thermal neutron peak deteriorated from 15% to 21%, and the figure of merit of pulse shape discrimination decreased from 1.41 to 1.16. These variation curves can be applied to evaluate and correct the detector irradiation damage.

Wakefield acceleration in the universe

The important role of magnetic fields in the phenomena in and evolution of the Universe is well appreciated. A salient example of this is to make (often episodic) large magnetic fields in AGN accretion disks and their emanation of well-collimated and longitudinally extended astrophysical jets. Such typical cases or related astrophysical processes, we find, provide a fertile ground for exciting large-amplitude oscillations in the magnetic fields that constitute the spine of the jets. The energy sources of these oscillations can be traced originally to the gravitational energy of the central object. During their long propagation along the jet, because of the gradual changes of the density and magnetic fields, these large magnetic pulsations turn into relativistic amplitude electromagnetic (EM) pulses, which in turn induce intense wakefields that are capable of acceleration of electrons, positrons, and ions to high energies. In this review, we survey a variety of astrophysical objects ranging from as large as the cosmic AGN accretion disks and their jets to as small as microquasars, to find or predict that there exist common astrophysical processes of emission of high-energy particles and gamma (and other EM) emissions. A variety of these objects will be ideally observed and studied in the multimessenger astrophysical observations. One example that already stuck out was the case of the simultaneous observations of gravitational wave emission and gamma-ray pulse from the collision of the two neutron stars and their subsequent structure formation (such as a disk) around them.

Inferring neutron star properties with continuous gravitational waves

ABSTRACT Detection of continuous gravitational waves from rapidly spinning neutron stars opens up the possibility of examining their internal physics. We develop a framework that leverages a future continuous gravitational wave detection to infer a neutron star’s moment of inertia, equatorial ellipticity, and the component of the magnetic dipole moment perpendicular to its rotation axis. We assume that the neutron star loses rotational kinetic energy through both gravitational wave and electromagnetic radiation, and that the distance to the neutron star can be measured, but do not assume electromagnetic pulsations are observable or a particular neutron star equation of state. We use the Fisher information matrix and Monte Carlo simulations to estimate errors in the inferred parameters, assuming a population of gravitational-wave-emitting neutron stars consistent with the typical parameter domains of continuous gravitational wave searches. After an observation time of 1 yr, the inferred errors for many neutron stars are limited chiefly by the error in the distance to the star. The techniques developed here will be useful if continuous gravitational waves are detected from a radio, X-ray, or gamma-ray pulsar, or else from a compact object with known distance, such as a supernova remnant.

The Green Bank North Celestial Cap Survey. VII. 12 New Pulsar Timing Solutions

We present timing solutions for 12 pulsars discovered in the Green Bank North Celestial Cap 350 MHz pulsar survey, including six millisecond pulsars (MSPs), a double neutron star (DNS) system, and a pulsar orbiting a massive white dwarf companion. Timing solutions presented here include 350 and 820 MHz Green Bank Telescope data from initial confirmation and follow-up, as well as a dedicated timing campaign spanning 1 ryr PSR J1122−3546 is an isolated MSP, PSRs J1221−0633 and J1317−0157 are MSPs in black widow systems and regularly exhibit eclipses, and PSRs J2022+2534 and J2039−3616 are MSPs that can be timed with high precision and have been included in pulsar timing array experiments seeking to detect low-frequency gravitational waves. PSRs J1221−0633 and J2039−3616 have Fermi Large Area Telescope gamma-ray counterparts and also exhibit significant gamma-ray pulsations. We measure proper motions for three of the MSPs in this sample and estimate their space velocities, which are typical compared to those of other MSPs. We have detected the advance of periastron for PSR J1018−1523 and therefore measure the total mass of the DNS system, m tot = 2.3 ± 0.3 M ⊙. Long-term pulsar timing with data spanning more than 1 yr is critical for classifying recycled pulsars, carrying out detailed astrometry studies, and shedding light on the wealth of information in these systems post-discovery.

Energetic requirements of the gamma-ray emission from pulsars: A nonparametric analysis of the data in the Fermi-LAT 12-Year Catalog

The prevalent view that the radio-loud gamma-ray pulsars have gamma-ray luminosities that exceed their radio luminosities by several orders of magnitude is based on the assumption that the decay with distance of their gamma-ray fluxes obeys the inverse-square law as does that of their radio fluxes. The results presented here, of testing the hypothesis of independence of luminosities and distances of gamma-ray pulsars by means of the Efron–Petrosian statistic, do not uphold this assumption however: they imply that the observational data in the Fermi-LAT 12-Year Catalog are consistent with the dependence S∝D−3/2 of the flux densities S of the gamma-ray pulsars on their distances D at substantially higher levels of significance than they are with the dependence S∝D−2. These results, which were theoretically predicted in Ardavan (2021), are not incompatible with the requirements of the conservation of energy because the radiation process by which the superluminally moving current sheet in the magnetosphere of a neutron star has been shown to generate the slowly decaying gamma-ray pulses is intrinsically transient: the difference in the fluxes of power across any two spheres centred on the star is balanced by the change with time of the energy contained inside the shell bounded by those spheres. Once the over-estimation of their values is rectified, the luminosities of gamma-ray pulsars turn out to have the same range of values as do the luminosities of radio pulsars. This conclusion agrees with that reached earlier on the basis of the smaller data set in the Second Fermi-LAT Catalog of Gamma-ray Pulsars.

The TRAPUM L-band survey for pulsars in Fermi-LAT gamma-ray sources

ABSTRACT More than 100 millisecond pulsars (MSPs) have been discovered in radio observations of gamma-ray sources detected by the Fermi Large Area Telescope (LAT), but hundreds of pulsar-like sources remain unidentified. Here, we present the first results from the targeted survey of Fermi-LAT sources being performed by the Transients and Pulsars with MeerKAT (TRAPUM) Large Survey Project. We observed 79 sources identified as possible gamma-ray pulsar candidates by a Random Forest classification of unassociated sources from the 4FGL catalogue. Each source was observed for 10 min on two separate epochs using MeerKAT’s L-band receiver (856–1712 MHz), with typical pulsed flux density sensitivities of $\sim 100\, \mu$Jy. Nine new MSPs were discovered, eight of which are in binary systems, including two eclipsing redbacks and one system, PSR J1526−2744, that appears to have a white dwarf companion in an unusually compact 5 h orbit. We obtained phase-connected timing solutions for two of these MSPs, enabling the detection of gamma-ray pulsations in the Fermi-LAT data. A follow-up search for continuous gravitational waves from PSR J1526−2744 in Advanced LIGO data using the resulting Fermi-LAT timing ephemeris yielded no detection, but sets an upper limit on the neutron star ellipticity of 2.45 × 10−8. We also detected X-ray emission from the redback PSR J1803−6707 in data from the first eROSITA all-sky survey, likely due to emission from an intrabinary shock.

Peculiarities of Excitation of a Particle in a Single-Level Quantum Well by an Extremely Short Attosecond Pulse

Using the solution of the time-dependent Schrodinger equation, the features of the excitation of a bound state of a particle in a one-dimensional rectangular quantum well of small depth by an extremely short light pulse are studied. The case of a shallow well with only one energy level is considered. In this case, the system is excited by an attosecond pulse whose duration is shorter than the characteristic time associated with the energy of the bound state of the particle in the well. It is shown that in this case the population of the bound state and the ionization probability are determined by the ratio of the electric area of the pulse to its atomic scale, which is inversely proportional to the well width. The calculation results showed that unipolar subcycle pulses with nonzero electric area can excite the system faster and more efficiently than bipolar pulses with zero area. The possibility of using unipolar gamma-ray pulses of zeptosecond duration for deuteron excitation is discussed, and numerical estimates of the required duration and electric area of the pulse are given. Keywords: extremely short pulses attosecond pulses, unipolar pulses, electric area of a pulse, atomic scale of electric area, one-dimensional quantum wells, nanostructures.

Особенности возбуждения частицы в одноуровневой квантовой яме предельно коротким аттосекундным импульсом

Using the solution of the time Schrödinger equation, the features of the excitation of a bound state of a particle in a one-dimensional rectangular quantum well of small depth by an extremely short light pulse are studied. The case of a shallow well with only one energy level is considered. In this case, the system is excited by an attosecond pulse whose duration is shorter than the characteristic time associated with the energy of the bound state of the particle in the well. It is shown that in this case the population of the bound state and the ionization probability are determined by the ratio of the electric area of the pulse to its atomic measure, which is inversely proportional to the well width. The calculation results showed that unipolar subcycle pulses with nonzero electric area can excite the system faster and more efficiently than bipolar pulses with zero area. The possibility of using unipolar gamma-ray pulses of zeptosecond duration for deuteron excitation is discussed, and numerical estimates of the required duration and electric area of the pulse are given.

Development of gamma-ray-induced positron age-momentum correlation measurement.

In conventional positron annihilation spectroscopy using radioisotopes, source contributions are unavoidable since positrons annihilate in the material covering the radioisotopes. Part of the positrons annihilate within the radioisotopes even when radioisotopes are deposited directly on a sample. Gamma-ray-induced positron annihilation spectroscopy makes it possible to measure only the spectra of a sample without source contributions since positrons are directly generated inside the sample from the gamma rays by pair production and annihilate inside the same sample. In this study, a new positron age-momentum correlation measurement system using ultrashort pulsed gamma rays is developed. The gamma rays with an energy of 6.6MeV are generated by the inverse Thomson scattering of laser photons by high-energy electrons and are irradiated to the sample. The laser pulse can fully control the timing of gamma-ray generation. This characteristic and the use of a digital oscilloscope with a 12-bit vertical resolution enable us to develop a simple measurement system. Time-resolved momentum distributions for stainless steel with no defects and deformed interstitial free steel show the explicit differences reflecting the type of defect; for BaF2 single crystals, the results have been interpreted by considering the formation of positronium.

Monte Carlo Simulation of Transient Response of Coaxial Cable Irradiated by Intense Pulsed Gamma Rays

To obtain the transient current law of typical coaxial cable irradiated by intense pulsed gamma rays, the irradiation effect experiment of intense pulsed gamma rays on typical coaxial cable was carried out on the “Qiangguang-1” accelerator, and the relationship between the amplitude of pulsed current in the center conductor of coaxial cable and the instantaneous gamma dose rate was measured. The simulation model of irradiation effect of intense pulsed gamma rays on the coaxial cable is presented. By using the Monte Carlo particle transport method, the electron charge deposition rate in the center conductor and the outer shielding conductor of different types of coaxial cables under intense pulsed gamma irradiation is calculated. The calculated results are basically consistent with the experimental results. When the gamma ray energy is greater than 0.6 MeV, the electron charge deposition rate in the center conductor of coaxial cable first increases, then decreases, and then increases with the increase of gamma ray energy. When the gamma ray energy is greater than 0.1 MeV, the number of electrons deposited in the center conductor of the cable per unit length increases with the increase of gamma ray energy. The number of electron charges deposited in the outer shielding conductor layer is greater than that deposited in the center conductor for typical coaxial cable. The gamma radiation sensitivity of the coaxial cable increases at the same gamma ray intensity when the cable is obliquely irradiated.

The Galactic population of canonical pulsars

Context. Current wisdom suggests that the observed population of neutron stars are manifestations of their birth scenarios and their thermal and magnetic field evolution. Neutron stars can be observed at various wavebands as pulsars, and radio pulsars represent by far the largest population of neutron stars. Aims. In this paper, we aim to constrain the observed population of the canonical neutron star period, its magnetic field, and its spatial distribution at birth in order to understand the radio and high-energy emission processes in a pulsar magnetosphere. For this purpose we design a population synthesis method, self-consistently taking into account the secular evolution of a force-free magnetosphere and the magnetic field decay. Methods. We generated a population of pulsars and evolved them from their birth to the present time, using the force-free approximation. We assumed a given initial distribution for the spin period, surface magnetic field, and spatial Galactic location. Radio emission properties were accounted for by the polar cap geometry, whereas the gamma-ray emission was assumed to be produced within the striped wind model. Results. We find that a decaying magnetic field gives better agreement with observations compared to a constant magnetic field model. Starting from an initial mean magnetic field strength of B = 2.5 × 108 T with a characteristic decay timescale of 4.6 × 105 yr, a neutron star birth rate of 1/70 yr and a mean initial spin period of 60 ms, we find that the force-free model satisfactorily reproduces the distribution of pulsars in the P−Ṗ diagram with simulated populations of radio-loud, radio-only, and radio quiet gamma-ray pulsars similar to the observed populations.

The SPAN512 mid-latitude pulsar survey at the Nançay Radio Telescope

Context. The large number of ongoing surveys for pulsars and transients at various radio observatories is motivated by the science obtained from these sources. Timing and polarisation analysis of relativistic binaries can place strong constraints on theories of gravity. The observation of a growing number of millisecond pulsars (MSPs) spread over the celestial sphere may allow the detection of a stochastic gravitational wave background arising from supermassive black hole binaries. A more complete sample of young pulsars improves our knowledge of neutron star birth and evolution. Transients such as fast radio bursts can serve to probe the intergalactic medium. Aims. The SPAN512 pulsar survey covers intermediate Galactic latitudes using the L-band receiver of the Nançay Radio Telescope (NRT). The survey covers 224 sq. deg. of the sky for a total exposure time of 2200 h. Population syntheses predict the discovery of 3 to 19 new normal pulsars and a few MSPs. Methods. We present detailed modelling of the NRT beam with its L-band receiver and its sensitivity which we used to precisely assess the expected survey yield. We used the flexible Pulsar Arecibo L-band Feed Array data processing pipeline to search the 47 TB of SPAN512 data for pulsars and transients. Results. The SPAN512 survey discovered two new MSPs and one new middle-aged pulsar. We focus on the analysis of the 2.4-ms spin period pulsar J2205+6012 for which we also report the detection of gamma-ray pulsations. Its narrow pulse width (35µs at an observing frequency of 2.55 GHz) allows for sub-microsecond timing precision over 8 yr, with exciting prospects for pulsar timing array programs.

Detection of the Farthest Globular Cluster NGC 6715 and Two Other GCs in Gamma-Rays with Fermi-LAT

In this paper, ∼12 yr long-term Pass 8 data from Fermi Large Area Telescope for the 157 globular clusters are carefully re-analyzed. Besides the 31 globular clusters reported in the fourth Fermi Large Area Telescope catalog Data Release 2, NGC 1851 is identified as a gamma-ray emitter and the significant gamma-ray emissions from NGC 6715 and NGC 6723 are detected. Especially NGC 6715 is located at a distance of 26.8 kpc, so far it is the farthest globular cluster detected in gamma-rays. A detailed analysis for these three globular clusters has been performed, but their gamma-ray pulsation emissions or flux variabilities are not found. The numbers of millisecond pulsars (MSPs) in these globular clusters are estimated under the assumption that each MSP inside globular clusters emits a similar amount of gamma-rays. Some possible origins of gamma-ray emission from globular clusters, such as MSPs, pulsar binary systems and/or dark matter, are discussed.

Development of a Signal Processing Software for Scintillation Detectors and Implementation on an FPGA for Fast Sensing

An open-source code RadSigPro 1.0 has been developed and used for fast processing of nanosecond-long pulses from scintillation detectors. This processing includes pulse height distribution (PHD), pulse shape discrimination (PSD), and time of flight (TOF). The code has been implemented onto the programmable logic design of a field programmable gate array (FPGA) design for on-the-fly processing of neutron and gamma-ray pulses. A weighted average of the percent difference of the results for RadSigPro 1.0 implemented on a CPU and a FPGA logic design is calculated. This shows a 0% difference for the PHD data sets, a 0.458% and 0.344% difference for the designated gamma detector and neutron detector PSD data sets, respectively, and a 0% difference for the TOF data set. When the FPGA logic design is applied and simulated, it computed the total and tail pulse areas within 5 ns of the arrival of the final data point used for accumulation and also captured the pulse height value within 2 ns of the arrival of the pulse’s maximum data point.

Synchro-curvature emitting regions in high-energy pulsar models

ABSTRACT The detected high-energy pulsars’ population is growing in number, and thus, having agile and physically relevant codes to analyse it consistently is important. Here, we update our existing synchro-curvature radiation model by including a better treatment of the particle injection, particularly where the large pitch angle particles dominate the spectra, and by implementing a fast and accurate minimization technique. The latter allows a large improvement in computational cost, needed to test model enhancements, and to apply the model to a larger pulsar population. We successfully fit the sample of pulsars with X-ray and gamma-ray data. Our results indicate that, for every emitting particle, the spatial extent of their trajectory where the pitch angle is large and most of the detected X-ray radiation is produced is a small fraction of the light cylinder. We also confirm with this new approach that synchrotron radiation is not negligible for most of the gamma-ray pulsars detected. In addition, with the results obtained, we argue that J0357+3205 and J2055+2539 are MeV pulsar candidates and are suggested for exhaustive observations in this energy band.