Context. Vela X-1 is one of the best-studied and most luminous accreting X-ray pulsars. The supergiant optical companion produces a strong radiatively driven stellar wind that is accreted onto the ...neutron star, producing highly variable X-ray emission. A complex phenomenology that is due to both gravitational and radiative effects needs to be taken into account to reproduce orbital spectral variations. Aims. We have investigated the spectral and light curve properties of the X-ray emission from Vela X-1 along the binary orbit. These studies allow constraining the stellar wind properties and its perturbations that are induced by the pulsating neutron star. Methods. We took advantage of the All Sky Monitor MAXI/GSC data to analyze Vela X-1 spectra and light curves. By studying the orbital profiles in the 4−10 and 10−20 keV energy bands, we extracted a sample of orbital light curves (~15% of the total) showing a dip around the inferior conjunction, that is, a double-peaked shape. We analyzed orbital phase-averaged and phase-resolved spectra of both the double-peaked and the standard sample. Results. The dip in the double-peaked sample needs NH ~ 2 × 1024cm-2 to be explained by absorption alone, which is not observed in our analysis. We show that Thomson scattering from an extended and ionized accretion wake can contribute to the observed dip. Fit by a cutoff power-law model, the two analyzed samples show orbital modulation of the photon index that hardens by ~0.3 around the inferior conjunction, compared to earlier and later phases. This indicates a possible inadequacy of this model. In contrast, including a partial covering component at certain orbital phase bins allows a constant photon index along the orbital phases, indicating a highly inhomogeneous environment whose column density has a local peak around the inferior conjunction. We discuss our results in the framework of possible scenarios.
We present the first MAXI/GSC X-ray source catalog in the low-Galactic-latitude sky outside the Galactic center region ( , l < 30°, and l > 330°) based on 7-year data from 2009 August 13 to 2016 July ...31. To overcome source confusion in crowded regions, we have accurately calibrated the position-dependent shape of the point-spread function of the MAXI/GSC by analyzing onboard data. We have also taken into account the Galactic ridge X-ray emission. Using a maximum likelihood image fitting method, we have detected 221 sources with a significance threshold >6.5 , 7 of which are transients only detected in 73-day time-sliced images. The faintest source has a flux of 5.2 × 10−12 erg cm−2 s−1 (or an intensity of 0.43 mCrab) in the 4-10 keV band. We have identified the counterparts for about 81% of the detected sources, by cross-matching with the Swift, Uhuru, RXTE, XMM-Newton, MCXC, and ROSAT all-sky survey catalogs. Our catalog contains the source name, position and its error, flux and detection significance in the 3-4 keV, 4-10 keV, and 10-20 keV bands, hardness ratios, and information on the likely counterpart for the individual detected sources. We have obtained 73-day bin light curves of all the cataloged sources over 7 years and have calculated their periodograms. On the basis of the mean properties of time variability and spectral hardness, we suggest that the majority of the unidentified sources are low-mass X-ray binaries or blazars. Finally, we present the log N-log S relations at different Galactic longitudes and for different source populations.
We present the third MAXI/GSC catalog in the high Galactic latitude sky ( ) based on the 7-year data from 2009 August 13 to 2016 July 31, complementary to that in the low Galactic latitude sky ( ) ...(Hori et al. 2018). We compile 682 sources detected at significances of sD,4-10 keV ≥ 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 0.48 mCrab, or 5.9 × 10−12 erg cm−2 s−1, over half of the survey area. Compared with the 37-month Hiroi et al. (2013) catalog, which adopted a threshold of sD,4-10 keV ≥ 7, the source number increases by a factor of ∼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 light curves in 1-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, as well as an X-ray galaxy cluster catalog (MCXC). Our catalog provides the fluxes, positions, detection significances, HRs, 1-year bin light curves, variability indices, and counterpart candidates.
The Super-Kamiokande detector Fukuda, S.; Hayakawa, T.; Ichihara, E. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2003, Letnik:
501, Številka:
2
Journal Article
Recenzirano
Super-Kamiokande is the world's largest water Cherenkov detector, with net mass 50,000 tons. During the period April, 1996 to July, 2001, Super-Kamiokande I collected 1678 live-days of data, ...observing neutrinos from the Sun, Earth's atmosphere, and the K2K long-baseline neutrino beam with high efficiency. These data provided crucial information for our current understanding of neutrino oscillations, as well as setting stringent limits on nucleon decay. In this paper, we describe the detector in detail, including its site, configuration, data acquisition equipment, online and offline software, and calibration systems which were used during Super-Kamiokande I.
A number of different fits to solar neutrino mixing and mass square difference were performed using 1496 days of Super-Kamiokande-I's solar neutrino data. These data select two allowed areas at large ...neutrino mixing when combined with either the solar
8B flux prediction of the standard solar model or the SNO interaction rate measurements. A global fit combining SK data with the solar neutrino interaction rates measured by Homestake, SNO, Gallex/GNO and SAGE prefers a single allowed area, the Large Mixing Angle solution, at the 98.9% confidence level. The mass square difference
Δm
2 between the two mass eigenstates ranges from about 3 to 19×10
−5 eV
2, while the mixing angle
θ is in the range of tan
2
θ≈0.25–0.65.
We study the process e+e- -> pi+pi-pi+pi-gamma, with a photon emitted from the initial-state electron or positron, using 454.3 fb^-1 of data collected with the BABAR detector at SLAC, corresponding ...to approximately 260,000 signal events. We use these data to extract the non-radiative sigma(e+e- ->pi+pi-pi+pi-) cross section in the energy range from 0.6 to 4.5 Gev. The total uncertainty of the cross section measurement in the peak region is less than 3%, higher in precision than the corresponding results obtained from energy scan data.
We report the result of a search for neutrino oscillations using precise measurements of the recoil electron energy spectrum and zenith angle variations of the solar neutrino flux from 1258 days of ...neutrino-electron scattering data in Super-Kamiokande. The absence of significant zenith angle variation and spectrum distortion places strong constraints on neutrino mixing and mass difference in a flux-independent way. Using the Super-Kamiokande flux measurement in addition, two allowed regions at large mixing are found.
We present the observation of an extraordinary luminous soft X-ray transient, MAXI J0158-744, by the Monitor of All-sky X-ray Image (MAXI) on 2011 November 11. This transient is characterized by a ...soft X-ray spectrum, a short duration (1.3 x 10 super(3) s < Delta T sub(d) < 1.10 x 10 super(4) s), a rapid rise (<5.5 x 10 super(3) s), and a huge peak luminosity of 2 x 10 super(40) erg s super(-1) in 0.7-7.0 keV band. With Swift observations and optical spectroscopy from the Small and Moderate Aperture Research Telescope System, we confirmed that the transient is a nova explosion, on a white dwarf in a binary with a Be star, located near the Small Magellanic Cloud. An early turn-on of the super-soft X-ray source (SSS) phase (<0.44 days), the short SSS phase duration of about one month, and a 0.92 keV neon emission line found in the third MAXI scan, 1296 s after the first detection, suggest that the explosion involves a small amount of ejecta and is produced on an unusually massive O-Ne white dwarf close to, or possibly over, the Chandrasekhar limit. We propose that the huge luminosity detected with MAXI was due to the fireball phase, a direct manifestation of the ignition of the thermonuclear runaway process in a nova explosion.
We present the results of the three-month above-ground commissioning run of the Large Underground Xenon (LUX) experiment at the Sanford Underground Research Facility located in Lead, South Dakota, ...USA. LUX is a 370kg liquid xenon detector that will search for cold dark matter in the form of Weakly Interacting Massive Particles (WIMPs). The commissioning run, conducted with the detector immersed in a water tank, validated the integration of the various sub-systems in preparation for the underground deployment. Using the data collected, we report excellent light collection properties, achieving 8.4 photoelectrons per keV for 662keV electron recoils without an applied electric field, measured in the center of the WIMP target. We also find good energy and position resolution in relatively high-energy interactions from a variety of internal and external sources. Finally, we have used the commissioning data to tune the optical properties of our simulation and report updated sensitivity projections for spin-independent WIMP-nucleon scattering.
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