Distance measurement of gamma-ray pulsars is a current challenge in pulsar studies.The Large Area Telescope（LAT） aboard the Fermi gamma-ray observatory discovered more than 70 gamma-ray pulsars including 24 new gamma-selected pulsars with almost no distance information.We study the relation between gammaray emission efficiency（η=Lγ/E˙） and pulsar parameters for young radio-selected gamma-ray pulsars with known distance information in the first gamma-ray pulsar catalog reported by Fermi/LAT.We have introduced three generation-order parameters to describe the gamma-ray emission properties of pulsars,and find a strong correlation of η-ζ3,a generation-order parameter which reflectsγ-ray photon generation in the pair cascade processes induced by magnetic field absorption in a pulsar＇s magnetosphere. A good correlation of η-BLC,the magnetic field at the light cylinder radius,is also found.These correlations are the distance indicators in gamma-ray pulsars used to evaluate distances for gamma-selected pulsars.Distances of 25 gamma-selected pulsars are estimated,which could be tested by other distance measurement methods.The physical origin of the correlations may also be interesting for pulsar studies.
We identify new strong lensing clusters of galaxies from the Sloan Digital Sky Survey Ⅲ （SDSS DR8） by visually inspecting color images of a large sample of clusters of galaxies. We find 68 new clusters showing giant arcs in addition to 30 known lensing systems. Among 68 cases, 13 clusters are ＂almost certain＂ lensing systems with tangential giant arcs, 22 clusters are ＂probable＂ and 31 clusters are ＂pos- sible＂ lensing systems. We also find two exotic systems with blue rings. The giant arcs have angular separations of 2.0jj - 25.7j~ from the bright central galaxies. We note that the rich clusters are more likely to be lensing systems and the separations between the arcs and the central galaxies increase with cluster richness.
A digital pulsar backend based on a Field Programmable Gate Array （FPGA） is developed. It is designed for incoherent de-dispersion of pulsar observations and has a maximum bandwidth of 512MHz. The channel bandwidth is fixed to 1 MHz, and the highest time resolution is 10 p.s. Testing observations were carried out using the Urumqi 25-m telescope administered by Xinjiang Astronomical Observatory and the Kunming 40-m telescope administered by Yunnan Observatories, targeting PSR J0332＋5434 in the L band and PSR J0437-4715 in the S band, respectively. The successful observation of PSR J0437-4715 demonstrates its ability to observe millisecond pulsars.
Recent INTEGRAL/IBIS hard X-ray surveys have detected about 10 young pulsars. We show hard X-ray properties of these 10 young pulsars, which have a luminosity of 10^33 - 10^37 erg s^-1 and a photon index of 1.6-2.1 in the energy range of 20-100 keV. The correlation between X-ray luminosity and spin-down power of Lx ∝ Lsd^1.31 suggests that the hard X-ray emission in rotation-powered pulsars is dominated by the pulsar wind nebula （PWN） component. Assuming spectral properties are similar in 20-100keV and 2-10 keV for both the pulsar and PWN components, the hard X-ray luminosity and flux of 39 known young X-ray pulsars and 8 millisecond pulsars are obtained, and a correlation of Lx ∝ Lsd^1.5 is derived. About 20 known young X-ray pulsars and 1 millisecond pulsars could be detected with future INTEGRAL and HXMT surveys. We also carry out Monte Carlo simulations of hard X-ray pulsars in the Galaxy and the Gould Belt, assuming values for the pulsar birth rate, initial position, proper motion velocity, period, and magnetic field distribution and evolution based on observational statistics and the Lx - Lsd reltions：Lx ∝Lsd^1.31 and Lx∝Lsd^1.5 More than 40 young pulsars （mostly in the Galactic plane） could be detected after ten years of INTEGRAL surveys and the launch of HXMT. So, the young pulsars would be a significant part of the hard X-ray source population in the sky, and will contribute to unidentified hard X-ray sources in present and future hard X-ray surveys by INTEGRAL and HXMT.
We report the discovery of 4 strong gravitational lensing systems by visual inspections of the Sloan Digital Sky Survey images of galaxy clusters in Data Release 6 （SDSS DR6）. Two of the four systems show Einstein rings while the others show tangen- tial giant arcs. These arcs or rings have large angular separations （〉 8″） from the bright central galaxies and show bluer color compared with the red cluster galaxies. In addition, we found 5 probable and 4 possible lenses by galaxy clusters.
Zhong-Lue WenJin-Lin HanXiang-Yang XuYun-Ying JiangZhi-Qing GuoPeng-Fei WangFeng-Shan Liu
Radio detection of pulsars in the Galactic disk is strongly affected by the dispersion and scattering effect of the interstellar medium and the Galactic background radio emission. In order to know the best conditions for discovery of pulsars, we select and simulate pulsar samples in the Galactic disk, and calculate the detection probability with various observation conditions (such as observational frequency, telescope aperture, receiver bandwidth and integration time). We have found that the detection fraction increases with the telescope aperture, receiver bandwidth and integration time. To detect pulsars in the nearer half of the Galactic disk, the observation frequency should be in the range of 1-2 GHz, while for pulsars in the farther half of the disk, the frequency should be in the range of 3.5-4.5 GHz. Due to the strong influence of scattering, the short period pulsars are hard to be detected, especially for pulsars in the farther half of the Galactic disk.
Pulsar hulling is a phenomenon of sudden cessation of pulse emission for a number of periods. The nulling fraction was often used to characterize the phenomenon. We propose a new method to analyse pulsar hulling phenomenon, by involving two key parameters, the nulling degree, X, which is defined as the angle in a rectangular coordinates for the numbers of nulling periods and bursting periods, and the nulling scale, N, which is defined as the effective length of the consecutive nulling periods and bursting periods. The nulling degree X can be calculated by tanX = Nnulling/Nbursting and the mean is related to the nulling fraction, while the nulling scale, N, is also a newly defined fundamental parameter which indicates how often the nulling occurs. We determined the distributions ofx and N for 10 pulsars by using the data in literature. We found that the nulling degree X indicates the relative length of nulling to that of bursting, and the nulling scale N is found to be related to the derivative of rotation frequency and hence the loss rate of rotational energy of pulsars. Their deviations reflect the randomness of the nulling process.
