119260012
Multiwavelength properties of a new Geminga-like pulsar: PSR J2021+4026
In this paper, we report on a detailed investigation of the multiwavelength properties of a newly detected gamma-ray pulsar, PSR J2021+4026, in both observational and theoretical aspects. We first identify an X-ray source in the XMM-Newton serendipitous source catalogue, 2XMM J202131.0+402645, located within the 95 per cent confidence circle of PSR J2021+4026. With an archival Chandra observation, this identification provides an X-ray position with arcsecond accuracy which is helpful in facilitating further investigations. Searching for the pulsed radio emission at the position of 2XMM J202131.0+402645 with a 25-m telescope at Urumqi Astronomical Observatory resulted in null detection and places an upper limit of 0.1 mJy for any pulsed signal at 18 cm. Together with the emission properties in X-ray and gamma-ray, the radio quietness suggests PSR J2021+4026 to be another member of Geminga-like pulsars. In the radio sky survey data, extended emission features have been identified in the gamma-ray error circle of PSR J2021+4026. We have also re-analysed the gamma-ray data collected by Fermi's Large Area Telescope. We found that the X-ray position of 2XMM J202131.0+402645 is consistent with that of the optimal gamma-ray timing solution. We have further modelled the results in the context of the outer gap model, which provides us with constraints for the pulsar emission geometry such as the magnetic inclination angle and the viewing angle. We have also discussed the possibility of whether PSR J2021+4026 has any physical association with the supernova remnant G78.2+2.1 (gamma-Cygni).
53583135
Three-dimensional two-layer outer gap model: Fermi energy-dependent light curves of the Vela pulsar
We extend the two-dimensional two-layer outer gap model to a three-dimensional geometry and use it to study the high-energy emission of the Vela pulsar. In this model, the outer gap is divided into two parts, i.e. the main acceleration region on the top of last-open field lines and the screening region around the upper boundary of the gap. In the main acceleration region, the charge density is much lower than the Goldreich–Julian charge density, and the charged particles are accelerated by the electric field along the magnetic field to emit multi-GeV photons. In the screening region, the charge density is larger than the Goldreich–Julian value to close the gap, and particles in this region are responsible for multi-100 MeV photon emission. We apply this three-dimensional two-layer model to the Vela pulsar and compare the model light curves, the phase-averaged spectrum and the phase-resolved spectra with the recent Fermi observations, which also reveals the existence of the third peak between two main peaks. The phase position of the third peak moves with the photon energy, which cannot be explained by the geometry of magnetic field structure and the caustic effects of the photon propagation. We suggest that the existence of the third peak and its energy-dependent movement results from the azimuthal structure of the outer gap.
118889930
POPULATION STUDY FOR γ-RAY PULSARS WITH THE OUTER GAP MODEL
Inspired by the increase of the population of {gamma}-ray emitting pulsars by the Fermi telescope, we perform a population study for {gamma}-ray emitting canonical pulsars. We use a Monte Carlo technique to simulate the Galactic population of neutron stars and the radio pulsars. For each simulated neutron star, we consider the {gamma}-ray emission from the outer gap accelerator in the magnetosphere. In our outer gap model, we apply the gap closure mechanism proposed by Takata et al., in which both photon-photon pair-creation and magnetic pair-creation processes are considered. Simulating the sensitivities of previous major radio surveys, our simulation predicts that there are {approx}18-23 radio-loud and {approx}26-34 {gamma}-ray-selected {gamma}-ray pulsars, which can be detected with a {gamma}-ray flux F{sub {gamma}} {>=} 10{sup -10} erg cm{sup -2} s{sup -1}. Applying the sensitivity of the six month observation of the Fermi telescope, 40-61 radio-selected and 36-75 {gamma}-ray selected pulsars are detected within our simulation. We show that the distributions of various pulsar parameters for the simulated {gamma}-ray pulsars can be consistent with the observed distribution of the {gamma}-ray pulsars detected by the Fermi telescope. We also predict that {approx}64 radio-loud and {approx}340 {gamma}-ray-selected pulsars irradiate the Earth with a flux F{sub {gamma}} {>=}more » 10{sup -11} erg cm{sup -2} s{sup -1}, and most of those {gamma}-ray pulsars are distributed with a distance greater than 1 kpc and a flux F{sub {gamma}} {approx} 10{sup -11} erg cm{sup -2} s{sup -1}. The ratio between the radio-selected and {gamma}-ray-selected pulsars depends on the sensitivity of the radio surveys. We also discuss the Galactic distribution of the unidentified Fermi sources and the canonical {gamma}-ray pulsars.« less
118161430
Population study for gamma-ray pulsars; II Millisecond pulsars
The population of $\gamma$-ray emitting millisecond pulsars (MSPs) is studied by using Monte-Carlo techniques. We simulate the Galactic distributions of the MSPs, and apply the outer gap model for the $\gamma$-ray emission from each simulated MSP. We take into account the dependence of the observed $\gamma$-ray flux on the viewing angle and inclination angle, which is the angle between the rotation axis and the magnetic axis, respectively. Using the sensitivity of the six-month long observation of the $Fermi$ telescope and radio sensitivities of existing pulsar surveys, 9-13 radio-selected and 22-35 $\gamma$-ray-selected pulsars are detected within our simulation. The statistical properties of the simulated population are consistent with the $Fermi$ observations. Scaling the observed sensitivity $\propto \sqrt{T}$, where $T$ is the length of observation time, the present model predicts that over the 5-year mission $Fermi$ would detect 15-22 radio-selected $\gamma$-ray MSPs, and 95-152 $\gamma$-ray-selected MSPs. Our simulation also predicts that about 100 (or 200-300) $\gamma$-ray MSPs with a flux larger $F\ge 10^{-11}~\mathrm{erg/cm^2 s}$ (or $5\times 10^{-12}~\mathrm{erg/cm^2 s}$) irradiate the Earth. With the present sensitivities of the radio surveys, most of them are categorized as $\gamma$-ray-selected pulsars, indicating that most of the $\gamma$-ray MSPs have been missed by the present $Fermi$ observations. We argue that the Galactic $Fermi$ unidentified sources located at high latitudes should be dominated by MSPs, whereas the sources in the galactic plane are dominated by radio-quiet canonical pulsars.
119299391
Outer gap accelerator closed by magnetic pair-creation process
We discuss outer gap closure mechanism in the trans-field direction with the magnetic pair-creation process near the stellar surface. The gap closure by the magnetic pair-creation is possible if some fraction of the pairs are produced with an outgoing momentum. By assuming that multiple magnetic field will affect the local field near the stellar surface, we show a specific magnetic field geometry near the stellar surface resulting in the outflow of the pairs. Together with the fact that the electric field is weak below null charge surface, the characteristic curvature photon energy emitted by incoming particles, which were accelerated in the outer gap, decreases drastically to ∼ 100MeV near the stellar surface. We estimate the height measured from the last-open field line, above which 100 MeV photons is converted into pairs by the magnetic pair-creation. We also show the resultant multiplicity due to the magnetic pair-creation process could acquire Me± ∼ 10− 10. In this model the fractional outer gap size is proportional to P. The predicted gamma-ray luminosity (Lγ) and the characteristic curvature photon energy (Ec) emitted from the outer gap are proportional to B P and BP respectively. This model also predicts that Lγ and Ec are related to the spin down power (Lsd) or the spin down age of pulsars (τ) as Lγ ∝ L 5/8 sd or Lγ ∝ τ , and Ec ∝ L 1/4 sd or Ec ∝ τ −1/2 respectively. Subject headings: pulsars: general– radiation mechanisms:non-thermal– -gamma rays:theory–magnetic field
118660389
TWO-PHASE ICM IN THE CENTRAL REGION OF THE RICH CLUSTER OF GALAXIES A1795: A JOINT CHANDRA, XMM-NEWTON, AND SUZAKU VIEW
Based on a detailed analysis of the high-quality Chandra, XMM-Newton, and Suzaku data of the X-ray bright cluster of galaxies A1795, we report clear evidence for a two-phase intracluster medium (ICM) structure, which consists of a cool (with a temperature T-c approximate to 2.0-2.2 keV) and a hot (T-h approximate to 5.0-5.7 keV) component that coexist and dominate the X-ray emission at least in the central 80 kpc. A third weak emission component (T-3 approximate to 0.8 keV) is also detected within the innermost 144 kpc and is ascribed to a portion of interstellar medium of the cD galaxy. Deprojected spectral analysis reveals flat radial temperature distributions for both the hot phase and cool phase components. These results are consistent with the ASCA measurements reported by Xu et al. and resemble the previous findings for the Centaurus Cluster. By analyzing the emission measure ratio and gas metal abundance maps created from the Chandra data, we find that the cool phase component is more metal-enriched than the hot phase one in the 50-100 kpc region, which agrees with that found in M87. The coexistence of the cool phase and hot phase ICM cannot be realized by bubble uplifting from active galactic nuclei (AGNs) alone. Instead, the two-phase ICM properties are better reconciled with a cD corona model. In this model, the cool phase may be ascribed to the plasmas confined in magnetic loops, which are surrounded by the intruding hot phase ICM and have been polluted by metals synthesized in the cD galaxy. AGN feedback energy released in the innermost 10 kpc can serve as the heating source to prevent the loop-interior gas from cooling down to temperatures much lower than the observed value. The total gravitating mass profile exhibits a hierarchical structure, regardless of the ICM temperature modeling.
122101803
First results on the hybrid photodiode tube
Abstract The performance of a new breed of light detectors based on a photocathode followed by a planar silicon diode working in the bombarding mode is reported. This detector was developed by the LAA project in order to produce a fast light detector capable of covering a span of the more than 4 orders of magnitude of linearity required by the scintillating fibre and lead (“spaghetti”) calorimeter. Linear signals from single, to more than 10 6 photoelectrons per pulse were measured. The general characteristics of this detector are reported here.
28167252
THE LAMOST SURVEY OF BACKGROUND QUASARS IN THE VICINITY OF THE ANDROMEDA AND TRIANGULUM GALAXIES. II. RESULTS FROM THE COMMISSIONING OBSERVATIONS AND THE PILOT SURVEYS
We present new quasars discovered in the vicinity of the Andromeda and Triangulum galaxies with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, also named the Guoshoujing Telescope, during the 2010 and 2011 observational seasons. Quasar candidates are selected based on the available Sloan Digital Sky Survey, Kitt Peak National Observatory 4 m telescope, Xuyi Schmidt Telescope Photometric Survey optical, and Wide-field Infrared Survey Explorer near-infrared photometric data. We present 509 new quasars discovered in a stripe of ~135 deg^2 from M31 to M33 along the Giant Stellar Stream in the 2011 pilot survey data sets, and also 17 new quasars discovered in an area of ~100 deg^2 that covers the central region and the southeastern halo of M31 in the 2010 commissioning data sets. These 526 new quasars have i magnitudes ranging from 15.5 to 20.0, redshifts from 0.1 to 3.2. They represent a significant increase of the number of identified quasars in the vicinity of M31 and M33. There are now 26, 62, and 139 known quasars in this region of the sky with i magnitudes brighter than 17.0, 17.5, and 18.0, respectively, of which 5, 20, and 75 are newly discovered. These bright quasars provide an invaluable collection with which to probe the kinematics and chemistry of the interstellar/intergalactic medium in the Local Group of galaxies. A total of 93 quasars are now known with locations within 2fdg5 of M31, of which 73 are newly discovered. Tens of quasars are now known to be located behind the Giant Stellar Stream, and hundreds are behind the extended halo and its associated substructures of M31. The much enlarged sample of known quasars in the vicinity of M31 and M33 can potentially be utilized to construct a perfect astrometric reference frame to measure the minute proper motions (PMs) of M31 and M33, along with the PMs of substructures associated with the Local Group of galaxies. Those PMs are some of the most fundamental properties of the Local Group.
16270452
A CHANDRA STUDY OF TEMPERATURE SUBSTRUCTURES IN INTERMEDIATE-REDSHIFT GALAXY CLUSTERS
By analyzing the gas temperature maps created from the Chandra archive data, we reveal the prevailing existence of temperature substructures on ~100 h –1 70 kpc scales in the central regions of nine intermediate-redshift (z ≈ 0.1) galaxy clusters, which resemble those found in the Virgo and Coma Clusters. Each substructure contains a clump of hot plasma whose temperature is about 2-3 keV higher than the environment, corresponding to an excess thermal energy of ~1058-1060 erg per clump. If there were no significant nongravitational heating sources, these substructures would have perished in 108-109 yr due to thermal conduction and turbulent flows, whose velocity is found to range from about 200 to 400 km s–1, we conclude that the substructures cannot be created and sustained by inhomogeneous radiative cooling. We also eliminate the possibilities that the temperature substructures are caused by supernova explosions, or by the nonthermal X-ray emission due to the inverse-Comptonization of the cosmic microwave background photons. By calculating the rising time of active galactic nucleus (AGN)-induced buoyant bubbles, we speculate that the intermittent AGN outbursts (≥1060 erg per burst) may have played a crucial role in the formation of the high-temperature substructures. Our results are supported by the recent study of McNamara and Nulsen, posing a tight observational constraint on future theoretical and numerical studies.
123544625
A new design of large area MCP-PMT for the next generation neutrino experiment
This manuscript discusses a new design of large area MCP-PMT for the next generation neutrino experiments. The main motivation of the design is to improve the quantum efficiency (photo detection efficiency) of the PMT. Two sets of small MCP units, the transmission photocathode coated on the front hemisphere and the reflection photocathode coated on the rear hemisphere are assembled in the same glass envelope to form nearly 4 pi viewing angle to enhance the efficiency of the photoelectron detection. The photoelectrons from the 4 pi photocathode are collected and amplified by two sets of MCP units. Our goal is eventually to produce 20 in. diameter PMT following such an approach. We will report preliminary results of our ptoelectronic simulation and the results of a 5 in. diameter prototype PMT. Future plans and prospects are discussed at the end. (C) 2011 Elsevier B.V. All rights reserved.