We present the catalog of high Galactic-latitude ($|b|>10^{circ}$) X-ray sources detected in the first 37-month data of Monitor of All-sky X-ray Image (MAXI) / Gas Slit Camera (GSC). To achieve the best sensitivity, we develop a background model of t
he GSC that well reproduces the data based on the detailed on-board calibration. Source detection is performed through image fit with the Poisson likelihood algorithm. The catalog contains 500 objects detected in the 4--10 keV band with significance of $s_{rm D, 4-10 keV} geq 7$. The limiting sensitivity is $approx 7.5times10^{-12}$ ergs cm$^{-2}$ s$^{-1}$ ($approx 0.6$ mCrab) in the 4--10 keV band for 50% of the survey area, which is the highest ever achieved as an all-sky survey mission covering this energy band. We summarize the statistical properties of the catalog and results from cross matching with the Swift/BAT 70-month catalog, the meta-catalog of X-ray detected clusters of galaxies, and the MAXI/GSC 7-month catalog. Our catalog lists the source name (2MAXI), position and its error, detection significances and fluxes in the 4--10 keV and 3--4 keV bands, their hardness ratio, and basic information of the likely counterpart available for 296 sources.
We study the comoving space density of X-ray-selected luminous active galactic nuclei (AGNs) and the obscured AGN fraction at high redshifts ($3 < z < 5$) in the Subaru/{it XMM-Newton} Deep Survey (SXDS) field. From an X-ray source catalog with high
completeness of optical identification thanks to deep optical images, we select a sample of 30 AGNs at $z > 3$ with intrinsic (de-absorbed and rest-frame 2--10 keV) luminosities of $L_{rm X} = 10^{44-45}$ erg s$^{-1}$ detected in the 0.5--2 keV band, consisting of 20 and 10 objects with spectroscopic and photometric redshifts, respectively. Utilizing the $1/V_{rm max}$ method, we confirm that the comoving space density of luminous AGNs decreases with redshift above $z > 3$. When combined with the {it Chandra}-COSMOS result of Civano et al. (2011), the density decline of AGNs with $L_{rm X} = 10^{44-45}$ erg s$^{-1}$ is well represented by a power law of $(1 + z)^{-6.2 pm 0.9}$. We also determine the fraction of X-ray obscured AGNs with $N_{rm H} > 10^{22}$ cm$^{-2}$ in the Compton-thin population to be 0.54$^{+0.17}_{-0.19}$, by carefully taking into account observational biases including the effects of photon statistics for each source. This result is consistent with an independent determination of the type-2 AGN fraction based on optical properties, for which the fraction is found to be 0.59$pm$0.09. Comparing our result with that obtained in the local Universe, we conclude that the obscured fraction of luminous AGNs increases significantly from $z=0$ to $z>3$ by a factor of 2.5$pm$1.1.
We construct a new X-ray (2--10 keV) luminosity function of Compton-thin active galactic nuclei (AGNs) in the local universe, using the first MAXI/GSC source catalog surveyed in the 4--10 keV band. The sample consists of 37 non-blazar AGNs at $z=0.00
2-0.2$, whose identification is highly ($>97%$) complete. We confirm the trend that the fraction of absorbed AGNs with $N_{rm H} > 10^{22}$ cm$^{-2}$ rapidly decreases against luminosity ($L_{rm X}$), from 0.73$pm$0.25 at $L_{rm X} = 10^{42-43.5}$ erg s$^{-1}$ to 0.12$pm0.09$ at $L_{rm X} = 10^{43.5-45.5}$ erg s$^{-1}$. The obtained luminosity function is well fitted with a smoothly connected double power-law model whose indices are $gamma_1 = 0.84$ (fixed) and $gamma_2 = 2.0pm0.2$ below and above the break luminosity, $L_{*} = 10^{43.3pm0.4}$ ergs s$^{-1}$, respectively. While the result of the MAXI/GSC agrees well with that of HEAO-1 at $L_{rm X} gtsim 10^{43.5}$ erg s$^{-1}$, it gives a larger number density at the lower luminosity range. Comparison between our luminosity function in the 2--10 keV band and that in the 14--195 keV band obtained from the Swift/BAT survey indicates that the averaged broad band spectra in the 2--200 keV band should depend on luminosity, approximated by $Gammasim1.7$ for $L_{rm X} ltsim 10^{44}$ erg s$^{-1}$ while $Gammasim 2.0$ for $L_{rm X} gtsim 10^{44}$ erg s$^{-1}$. This trend is confirmed by the correlation between the luminosities in the 2--10 keV and 14--195 keV bands in our sample. We argue that there is no contradiction in the luminosity functions between above and below 10 keV once this effect is taken into account.
We present the first unbiased source catalog of the Monitor of All-sky X-ray Image (MAXI) mission at high Galactic latitudes ($|b| > 10^{circ}$), produced from the first 7-month data (2009 September 1 to 2010 March 31) of the Gas Slit Camera in the 4
--10 keV band. We develop an analysis procedure to detect faint sources from the MAXI data, utilizing a maximum likelihood image fitting method, where the image response, background, and detailed observational conditions are taken into account. The catalog consists of 143 X-ray sources above 7 sigma significance level with a limiting sensitivity of $sim1.5times10^{-11}$ ergs cm$^{-2}$ s$^{-1}$ (1.2 mCrab) in the 4--10 keV band. Among them, we identify 38 Galactic/LMC/SMC objects, 48 galaxy clusters, 39 Seyfert galaxies, 12 blazars, and 1 galaxy. Other 4 sources are confused with multiple objects, and one remains unidentified. The log $N$ - log $S$ relation of extragalactic objects is in a good agreement with the HEAO-1 A-2 result, although the list of the brightest AGNs in the entire sky has significantly changed since that in 30 years ago.
We carried out an international spectroscopic observation campaign of the dwarf nova GW Librae (GW Lib) during the 2007 superoutburst. Our observation period covered the rising phase of the superoutburst, maximum, slowly decaying phase (plateau), and
long fading tail after the rapid decline from the plateau. The spectral features dramatically changed during the observations. In the rising phase, only absorption lines of H$alpha$, H$beta$, and H$gamma$ were present. Around the maximum, the spectrum showed singly-peaked emission lines of H$alpha$, He I 5876, He I 6678, He II 4686, and C III/N III as well as absorption lines of Balmer components and He I. These emission lines significantly weakened in the latter part of the plateau phase. In the fading tail, all the Balmer lines and He I 6678 were in emission, as observed in quiescence. We find that the center of the H$alpha$ emission component was mostly stable over the whole orbital phase, being consistent with the low inclination of the system. Comparing with the observational results of WZ Sge during the 2001 superoutburst, the same type of stars as GW Lib seen with a high inclination angle, we interpret that the change of the H$alpha$ profile before the fading tail phase is attributed to a photoionized region formed at the outer edge of the accretion disk, irradiated from the white dwarf and inner disk.
