119402342
ROSAC: Studying the clustering properties of X-ray selected AGNs
We present the first ROSAC results of an AGN clustering analysis. This study comprises a sample of 200 AGNs, 75% of which being at low redshifts z<0.5, in the Ursa Major constellation. The spatial 2-point-correlation function (SCF) as well as the minimal spanning tree (MST) technique were applied. Some evidence for clustering is found in the SCF, although with low significance. Using the MST technique, we could find two AGN groups. This result is preliminary and the exact significance will be tested with careful simulations.
11077788
A GRB Follow-up System at the Xinglong Observatory and Detection of the High-Redshift GRB 060927 ⋆
A gamma-ray burst (GRB) optical photometric follow-up system at the Xinglong Observatory of National Astronomical Observatories of China (NAOC) has been constructed. It uses the 0.8-m Tsinghua-NAOC Telescope (TNT) and the 1-m EST telescope, and can automatically respond to GRB Coordinates Network (GCN) alerts. Both telescopes slew relatively fast, being able to point to a new target field within ~1 min upon a request. Whenever available, the 2.16-m NAOC telescope is also used. In 2006 the system responded to 15 GRBs and detected seven early afterglows. In 2007 six GRBs have been detected among 18 follow-up observations. TNT observations of the second most distant GRB 060927 (z = 5.5) are shown, which started as early as 91 s after the GRB trigger. The afterglow was detected in the combined image of the first 19×20 s unfiltered exposures. This GRB follow-up system has joined the East-Asia GRB Follow-up Observation Network (EAFON).
2493678
Large-scale structures in the distribution of X-ray selected AGN
We are searching for large-scale structures in the distribution of AGN discovered by the ROSAT All-Sky Survey. The RASS detected > 60000 X-ray objects, of which approximately 35% are AGN at z < 0.5. The surface density in the extragalactic sky is approximately 0.5 AGN/deg^2, which has not been reached until now by any other survey for this redshift range. We efficiently single out the AGN among all the RASS sources using the Hamburg/RASS database of optical identifications, which contains presently 13867 entries. 
Follow-up spectroscopy of RASS AGN candidates identified in selected areas of the northern sky is underway to determine the spatial distribution of the AGN in these areas. In every area structures reminiscent of clusters and filaments are found on scales 50 - 100 h^{-1}Mpc. These structures have a similar size as the serendipitously discovered groups of AGN in optical surveys at higher redshifts. Samples of low redshift AGN drawn from the RASS are large enough to be used with samples of higher redshift to study evolutionary effects in the large-scale distribution of AGN.
14732557
Very early multi-color observations of the plateau phase of GRB 041006 afterglow
Observations of the optical afterglow of GRB 041006 with the Kiso Observatory 1.05 m Schmidt telescope, the Lulin Observatory 1.0 m telescope and the Xinglong Observatory 0.6 m telescope. Three-bands (B, V and R) of photometric data points were obtained on 2004 October 6, 0.025−0.329 days after the burst. These very early multi band light curves imply the existence of a color dependent plateau phase. The B-band light curve shows a clear plateau at around 0.03 days after the burst. The R band light curve shows the hint of a plateau, or a possible slope change, at around 0.1 days after the burst. The overall behavior of these multi-band light curves may be interpreted in terms of the sum of two separate components, one showing a monotonic decay the other exhibiting a rising and a falling phase, as described by the standard afterglow model. Department of Physics, Saitama University, Shimo-Okubo, Saitama, 338-8570, Japan RIKEN (Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan, Republic of China National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan Kiso Observatory, Institute of Astronomy, The University of Tokyo, Mitake-mura, Kiso-gun, Nagano 397-0101, Japan Ulugh Beg Astronomical Institute, Tashkent 700052, Uzbekistan Space Research Institute, 84/32 Profsoyuznaya Str, Moscow 117997, Russia Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
16983032
Optical and radio variability of the BL Lacertae object AO 0235+16: A possible 5-6 year periodicity
The BL Lacertae object AO 0235+16 is well known for its extreme optical and radio variability. New optical and radio data have been collected in the last four years by a wide international collaboration, which conrm the intense activity of this source: on the long term, overall variations of 5 mag in the R band and up to a factor 18 in the radio fluxes were detected, while short-term variability up to 0:5 mag in a few hours and 1: 3m ag in one day was observed in the optical band. The optical data also include the results of the Whole Earth Blazar Telescope (WEBT) rst-light campaign organized in November 1997, involving a dozen optical observatories. The optical spectrum is observed to basically steepen when the source gets fainter. We have investigated the existence of typical variability time scales and of possible correlations between the optical and radio emissions by means of visual inspection and Discrete Correlation Function (DCF) analysis. On the long term, the autocorrelation function of the optical data shows a double-peaked maximum at 4100{4200 days (11:2{11:5 years), while a double-peaked maximum at 3900{4200 days (10:7{11:5 years) is visible in the radio autocorrelation functions. The existence of this similar characteristic time scale of variability in the two bands is by itself an indication of optical-radio correlation. A further analysis by means of Discrete Fourier Transform (DFT) technique and folded light curves reveals that the major radio outbursts repeat quasi-regularly with a periodicity of5:7 years, i.e. half the above time scale. This period is also in agreement with the occurrence of some of the major optical outbursts, but not all of them. Visual inspection and DCF analysis of the optical and radio light curves then reveal that in some cases optical outbursts seem to be simultaneous with radio ones, but in other cases they lead the radio events. Moreover, a deep inspection of the radio light curves suggests that in at least two occasions (the 1992{1993 and 1998 outbursts) flux variations at the higher frequencies may have led those at the lower ones.
95137172
Soft x-ray imaging and spectroscopy of single nanocrystals
Resonant photoemission electron microscopy (PEEM) at the Fe L3,2 absorption edge was utilized to image single γ-Fe2O3 nanocrystals of 10 nm average diameter (∼20 000 Fe atoms) and to record soft x-ray absorption spectra of individual particles. Within the spectral resolution of the experiment, no damage to the individual nanoparticles occurs during repeated, prolonged exposure to the intense x-ray beam. Furthermore, no differences in the position or shape of the soft x-ray absorption spectrum of a single nanocrystal and the ensemble are observed within the experimental resolution. PEEM contrast images and soft x-ray absorption spectra, however, show strong intensity variations between different particles reflecting the size distribution of the sample. This proof-of-principle experiment successfully demonstrates the applicability of x-ray spectromicroscopy to the study of nanoscale systems on a hitherto unachieved length scale.
119256368
The properties of a large sample of low surface brightness galaxies from SDSS
A large sample of low surface brightness (LSB) disk galaxies is selected from SDSS with B-band central surface brightness mu_0(B) from 22 to 24.5 mag arcsec^(-2). Some of their properties are studied, such as magnitudes, surface brightness, scalelengths, colors, metallicities, stellar populations, stellar masses and multiwavelength SEDs from UV to IR etc. These properties of LSB galaxies have been compared with those of the galaxies with higher surface brightnesses. Then we check the variations of these properties following surface brightness.
1567381
The structure of the Galactic halo : SDSS versus SuperCOSMOS
The halo structure at high Galactic latitudes near both the north and south poles is studied using Sloan Digital Sky Survey (SDSS) and SuperCOSMOS data. For the south cap halo, the archive of the SuperCOSMOS photographic photometry sky survey is used. The coincident source rate between SuperCOSMOS data in B J band from 16.5 to 20.5 mag and SDSS data is about 92 per cent, in a common sky area in the south. While that in the R F band is about 85 per cent from 16.5 to 19.5 mag. Transformed to the SuperCOSMOS system and downgraded to the limiting magnitudes of SuperCOSMOS, the star counts in the North Galactic Cap from SDSS show up to an 16.9±6.3 per cent asymmetric ratio (defined as relative fluctuations over the rotational symmetry structure) in the B J band, and up to 13.5 ± 6.7 per cent asymmetric ratio in the R F band. From SuperCOSMOS Bj and R F bands, the structure of the Southern Galactic hemisphere does not show the same obvious asymmetric structures as the northern sky does in both the original and downgraded SDSS star counts. An axisymmetric halo model with n = 2.8 and q = 0.7 can fit the projected number density from SuperCOSMOS fairly well, with an average error of about 9.17 per cent. By careful analysis of the difference of star counts between the downgraded SDSS northern halo data and SuperCOSMOS southern halo data, it is shown that no asymmetry can be detected in the South Galactic Cap at the accuracy of SuperCOSMOS, and the Virgo overdensity is likely a foreign component in the Galactic halo.
123336656
The importance of pion and extended Brueckner–Hartree–Fock theory
Abstract The pion is important in nuclear physics. The fact that the pion is a pseudoscalar particle makes it very difficult to treat explicitly in the nuclear many-body problem. Matrix elements of the tensor component in the pion exchange interaction vanish in the spin-saturated Hartree–Fock (HF) state. Hence, we are forced to include 2 p − 2 h excitations from the HF state in the model space and use the variational principle to get an extended differential equation for single particle states in the HF state. The structure of this differential equation resembles to that of the Brueckner–Hartree–Fock (BHF) theory and we name the new many-body framework as extended BHF (EBHF) theory. We discuss the similarity and difference between the BHF and EBHF theories. We apply the EBHF theory to nuclear matter and study the equation of state (EOS) and the occupation probability of high momentum states.
123272027
Extension of Hartree–Fock theory including tensor correlation in nuclear matter
Extension of Hartree–Fock theory including tensor correlation in nuclear matter Jinniu Hu1,2,∗,†, Hiroshi Toki1,∗,†, and Yoko Ogawa1,∗,† 1Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki, Osaka 567-0047, Japan 2State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China ∗E-mail: jinniuhu@rcnp.osaka-u.ac.jp (JH), toki@rcnp.osaka-u.ac.jp (HT), ogaway@rcnp.osaka-u.ac.jp (YO)
14866078
The asymmetric structure of the Galactic halo
Using the stellar photometry catalogue based on the latest data release (DR4) of the Sloan Digital Sky Survey (SDSS), a study of the Galactic structure using star counts is carried out for selected areas of the sky. The sample areas are selected along a circle at a Galactic latitude of +60 ◦ , and 10 strips of high Galactic latitude along different longitudes. Direct statistics of the data show that the surface densities of l from 180 ◦ to 360 ◦ are systematically higher than those of l from 0 ◦ to 180 ◦ , defining a region of overdensity (in the direction of Virgo) and another one of underdensity (in the direction of Ursa Major) with respect to an axisymmetric model. It is shown by comparing the results from star counts in the (g r) colour that the density deviations are due to an asymmetry of the stellar density in the halo. Theoretical models for the surface density profile are built and star counts are performed using a triaxial halo of which the parameters are constrained by observational data. Two possible reasons for the asymmetric structure are discussed.