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Register a new userThe 37-month MAXI/GSC source catalog in the high Galactic-latitude sky
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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 the 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.
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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 present the third MAXI/GSC catalog in the high Galactic-latitude sky ($|b| > 10^circ$) based on the 7-year data from 2009 August 13 to 2016 July 31, complementary to that in the low Galactic-latitude sky ($|b| < 10^circ$; Hori et al. 2018). We compile 682 sources detected at significances of $s_{rm D,4-10~keV} geq 6.5$ in the 4--10 keV band. A two-dimensional image fit based on the Poisson likelihood algorithm ($C$-statistics) is adopted for the detections and constraints on their fluxes and positions. The 4--10 keV sensitivity reaches $approx 0.48$ mCrab, or $approx 5.9 times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$, over the half of the survey area. Compared with the 37-month catalog (Hiroi et al. 2013), which adopted a threshold of $s_{rm D,4-10~keV} geq 7$, the source number increases by a factor of $sim$1.4. The fluxes in the 3--4 keV and 10--20 keV bands are further estimated, and hardness ratios (HRs) are calculated using the 3--4 keV, 4--10 keV, 3--10 keV, and 10--20 keV band fluxes. We also make the 4--10 keV lightcurves in one year bins for all the sources and characterize their variabilities with an index based on a likelihood function and the excess variance. Possible counterparts are found from five major X-ray survey catalogs by Swift, Uhuru, RXTE, XMM-Newton, and ROSAT, and an X-ray galaxy-cluster catalog (MCXC). Our catalog provides the fluxes, positions, detection significances, HRs, one-year bin lightcurves, variability indices, and counterpart candidates.
We report on preliminary results from the Fermi High-Latitude Extended Sources Catalog (FHES), a comprehensive search for spatially extended gamma-ray sources at high Galactic latitudes ($|b|>5^circ$) based on data from the Fermi Large Area Telescope (LAT). While the majority of high-latitude LAT sources are extragalactic blazars that appear point-like within the LAT angular resolution, there are several physics scenarios that predict the existence of populations of spatially extended sources. If Dark Matter consists of Weakly Interacting Massive Particles, the annihilation or decay of these particles in subhalos of the Milky Way would appear as a population of unassociated gamma-ray sources with finite angular extent. Gamma-ray emission from blazars could also be extended (so-called pair halos) due to the deflection of electron-positron pairs in the intergalactic magnetic field (IGMF). The pairs are produced in the absorption of gamma rays in the intergalactic medium and subsequently up-scatter photons of background radiation fields to gamma-ray energies. Measurement of pair halos could provide constraints on the strength and coherence length scale of the IGMF. In a dedicated search, we find 21 extended sources and 16 sources not previously characterized as extended. Limits on the flux of the extended source components are used to derive constraints on the strength of the IGMF using spectral and spatial templates derived from Monte Carlo simulations of electromagnetic cascades. This allows us to constrain the IGMF to be stronger than $3times10^{-16},$G for a coherence length $lambda gtrsim 10,$kpc.
We present the first results on the new black hole candidate, MAXI J1305-704, observed by MAXI/GSC. The new X-ray transient, named as MAXI J1305-704, was first detected by the MAXI-GSC all-sky survey on 2012 April 9 in the direction to the outer Galactic bulge at (l,b)=(304.2deg,-7.6deg). The Swift/XRT follow-up observation confirmed the uncatalogued point source and localized to the position at (13h06m56s.44,-70d274.91). The source continued the activity for about five months until 2012 August. The MAXI/GSC light curve in the 2--10 keV band and the variation of the hardness ratio of the 4-10 keV to the 2-4 keV flux revealed the hard-to-soft state transition on the the sixth day (April 15) in the brightening phase and the soft-to-hard transition on the ~60th day (June 15) in the decay phase. The luminosity at the initial hard-to-soft transition was significantly higher than that at the soft-to-hard transition in the decay phase. The X-ray spectra in the hard state are represented by a single power-law model with a photon index of ~2.0, while those in the soft state need such an additional soft component as represented by a multi-color disk blackbody emission with an inner disk temperature ~0.5--1.2 keV. All the obtained features support the source identification of a Galactic black-hole binary located in the Galactic bulge.
We present the first full catalog and science results for the NuSTAR serendipitous survey. The catalog incorporates data taken during the first 40 months of NuSTAR operation, which provide ~20Ms of effective exposure time over 331 fields, with an areal coverage of 13 sq deg, and 497 sources detected in total over the 3-24 keV energy range. There are 276 sources with spectroscopic redshifts and classifications, largely resulting from our extensive campaign of ground-based spectroscopic followup. We characterize the overall sample in terms of the X-ray, optical, and infrared source properties. The sample is primarily comprised of active galactic nuclei (AGNs), detected over a large range in redshift from z = 0.002 - 3.4 (median of <z> = 0.56), but also includes 16 spectroscopically confirmed Galactic sources. There is a large range in X-ray flux, from log( f_3-24keV / erg s^-1 cm^-2 ) ~ -14 to -11, and in rest-frame 10-40 keV luminosity, from log( L_10-40keV / erg s^-1 ) ~ 39 to 46, with a median of 44.1. Approximately 79% of the NuSTAR sources have lower energy (<10 keV) X-ray counterparts from XMM-Newton, Chandra, and Swift/XRT. The mid-infrared (MIR) analysis, using WISE all-sky survey data, shows that MIR AGN color selections miss a large fraction of the NuSTAR-selected AGN population, from ~15% at the highest luminosities (Lx > 10^44 erg s^-1) to ~80% at the lowest luminosities (Lx < 10^43 erg s^-1). Our optical spectroscopic analysis finds that the observed fraction of optically obscured AGNs (i.e., the Type 2 fraction) is F_Type2 = 53(+14-15)%, for a well-defined subset of the 8-24 keV selected sample. This is higher, albeit at a low significance level, than the Type 2 fraction measured for redshift- and luminosity-matched AGNs selected by <10 keV X-ray missions.
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