Rubin-LSST

Abstract:

We report recent Chandra observations of the ULX in the elliptical galaxy NGC 3379 that clearly detect two flux variability cycles. Comparing these data with the Chandra observation of ∼5 years ago, we measure a flux modulation with a period of ∼12.6 hr. Moreover, we find that the emission undergoes a correlated spectral modulation, becoming softer at low flux. We argue that our results establish this source as a ULX binary in NGC 3379. Given the old stellar population of this galaxy, the ULX is likely to be a soft transient; however, historical X-ray sampling suggests that the current "on" phase has lasted ∼10yr. We discuss our results in terms of ADC and wind-feedback models. If the flux modulation is orbital, we can constrain the donor mass and orbital period at the onset of mass transfer within 1.15-1.4 Ṁ and 12.5-17 hr, respectively. The duration of the mass transfer phase so far is probably ∼ 1 Gyr, and the binary has been a soft X-ray transient throughout this time. These constraints are insensitive to the mass of the accretor. © 2006. The American Astronomical Society. All rights reserved.

Abstract:

We report a measurement of the tt̄ production cross section using the CDF II detector at the Fermilab Tevatron. The analysis is performed using 311pb-1 of pp̄ collisions at s=1.96TeV. The data consist of events selected with six or more hadronic jets with additional kinematic requirements. At least one of these jets must be identified as a b-quark jet by the reconstruction of a secondary vertex. The cross section is measured to be σtt̄=7. 5±2.1(stat.)-2.2+3.3(syst.)-0.4+0.5(lumi.)pb, which is consistent with the standard model prediction. © 2006 The American Physical Society.