13913450
Ten Overdensities and an Arc Structure in the Galactic Halo
Aims. We use Sloan Digital Sky Survey (SDSS) DR5 photometric data to explore the structure of the Galaxy halo and hope to discover new companions or substructures which may reveal the forming history of the halo. Methods. We study overdensities in a sky area where � = 120 ◦ � 270 ◦ and � = 25 ◦ � 70 ◦ and pick out ten overdensity areas by comparing color-magnitude diagrams with known globular clusters or dwarf spheroidal galaxies. An automatic template matching method is developed to fit the color-magnitude diagram for ea ch overdensities with a suitable stellar evolution isochro nic line so that distance module and metalicity are roughly estimated. The performance test of the method indicates that our estimates on distance is acceptable. Results. The 10 overdensities and three known objects, UMa I, UMa II and Willman 1 are found to be connected with a long arc substructure starts from � 8kpc above the disk and spread to � 150kpc into north galactic cap. Evidence also shows a relationship between metalicities and distance modules of the overdensities. Conclusions. C7, one of the 10 overdensities is most likely a dwarf spheroidal galaxy according to radial density profile study and its absolute magnitude. Other overdensties are not classifi ed for poor information. The arc structure may either be a long tidal stream or be an intrinsic substructure of the halo. Follow-up study need to be done to clarify this problem.
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.
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
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.
2927391
A large sample of low surface brightness disc galaxies from the SDSS – I. The sample and the stellar populations
We present the properties of a large sample (12 282) of nearly face-on low surface brightness (LSB) disc galaxies selected from the main galaxy sample of SDSS-DR4. These properties include B-band central surface brightness μ 0 (B), scalelengths h, integrated magnitudes, colours and distances D. This sample has μ 0 (B) values from 22 to 24.5 mag arcsec -2 with a median value of 22.42 mag arcsec -2 , and disc scalelengths ranging from 2 to 19 kpc. They are quite bright with M B taking values from -18 to -23 mag with a median value of -20.08 mag. There exist clear correlations between log h and M B , log h and log D, log D and M B . However, no obvious correlations are found between μ 0 (B) and log h, colours, etc. The correlation between colours and log h is weak even though it exists. Both the optical-optical and optical-NIR colour-colour diagrams indicate that most of them have a mixture of young and old stellar populations. They also satisfy colour-magnitude relations, which indicate that brighter galaxies tend generally to be redder. The comparison between the LSBGs and a control sample of nearly face-on disc galaxies with higher surface brightness (HSB) with μ 0 (B) from 18.5 to 22 mag arcsec -2 show that, at a given luminosity or distance, the observed LSB galaxies tend to have larger scalelengths. These trends could be seen gradually by dividing both the LSBGs and HSBGs into two subgroups according to surface brightness. A volume-limited subsample was extracted to check the incompleteness of surface brightness. The only one of the property relations having an obvious change is the relation of log h versus μ 0 (B), which shows a correlation in this subsample.
123828193
Effective Λn potential from relativistic Brueckner-Hartree-Fock theory
118442181
GRB 070518: a gamma-ray burst with optically dim luminosity
We present our optical observations of the GRB 070518 afterglow obtained at the 0.8-m Tsinghua University-National Astronomical Observatory of China Telescope (TNT) at Xinglong Observatory. Our follow-up observations were performed from 512 s after the burst trigger. With the upper limit of redshift ~0.7, GRB 070518 is found to be an optically dim burst. The spectra indices β ox of optical to X-ray are slightly larger than 0.5, which implies that the burst might be a dark burst. The extinction A V of the host galaxy is 3.2 mag, inferred from the X-ray hydrogen column density with Galactic extinction law, and 0.3 mag with the Small Magellanic Cloud extinction law. Also, it is similar to three other low-redshift optically dim bursts, which belong to X-ray rich gamma-ray bursts or X-ray flashes and have mid-term duration (T 90 < 10, except for GRB 070419A, T 90 £= 116 s). Moreover, its R-band afterglow flux is well fitted by a single power law with an index of 0.87. The optical afterglow and the X-ray afterglow in the normal segment might have the same mechanism, as they are consistent with the prediction of the classical external shock model. Besides, GRB 070518 agrees with the Amati relation under reasonable assumptions. The Ghirlanda relation is also tested with the burst.
14520300
Distance Determination of Variable Galactic Sources
We have developed a timing analysis method to determine the distances of variable galactic X-ray sources based on the method advanced by Trumper and Schonfelder in 1973. The light-curve of the halo produced by the scattering of X-rays off the interstellar dust is delayed and smeared by the dust grains. This method utilizes the differences between the power density spectra of the point source and the halo. We present the details of this method and our first applications of this method to the Chandra data of X-ray binary Cyg X-3.
117824458
A confirmative spin-parity assignment for the key 6.15 MeV state in $^{18}$Ne of astrophysical importance
Proton resonant states in $^{18}$Ne have been investigated by the resonant elastic scattering of $^{17}$F+$p$. The $^{17}$F beam was separated by the CNS radioactive ion beam separator (CRIB), and bombarded a thick H$_2$ gas target at 3.6 MeV/nucleon. The recoiled light particles were measured by using three sets of ${\Delta}$E-E Si telescope at scattering angles of $\theta$$_{lab}$$\approx 3^\circ$, 10$^\circ$ and 18$^\circ$, respectively. Four resonances, {\it i.e.}, at $E_{x}$=6.15, 6.30, 6.85, and 7.05 MeV, were observed clearly. By $R$-matrix analysis of the excitation functions, $J^{\pi}$=1$^-$ was firmly assigned to the 6.15 MeV state which is a key state in calculating the reaction rate of $^{14}$O($\alpha$,$p$)$^{17}$F reaction. This reaction was thought to be one of the most probable key reactions for the breakout from the hot-CNO cycle to the $rp$-process in type I x-ray bursts In addition, a new excited state observed at $E_{x}$=6.85 MeV was tentatively assigned as 0$^{-}$, which could be the analog state of 6.880 MeV, 0$^{-}$ in mirror $^{18}$O.