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Register a new userConstraining the spectral parameters of RXJ0925.7-4758 with the BeppoSAX LECS
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The Super Soft Source RX J0925.7--4758 was observed by BeppoSAX LECS and MECS on January 25--26 1997. The source was clearly detected by the LECS but only marginally detected by the MECS. We apply detailed Non-Local Thermodynamic Equilibrium (Non-LTE) models including metal line opacities to the observed LECS spectrum. We test whether the X-ray spectrum of RX J0925 is consistent with that of a white dwarf and put constraints upon the effective temperature and surface gravity by considering the presence or absence of spectral features such as absorption edges and line blends in the models and the observed spectrum. We find that models with effective temperatures above ~1e6 K or below ~7.5e5 K can be excluded. If we assume a single model component for RX J0925 we observe a significant discrepancy between the model and the data above the NeIX edge energy at 1.19 keV. This is consistent with earlier observations with ROSAT and ASCA. The only way to account for the emission above ~1.2 keV is by introducing a second spectral (plasma) component. This plasma component may be explained by a shocked wind originating from the compact object or from the irradiated companion star. If we assume log g = 9 then the derived luminosity is consistent with that of a nuclear burning white dwarf at a distance of ~4 kpc.
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Gravitational-wave detectors have begun to observe coalescences of heavy black holes at a consistent pace for the past few years. Accurate models of gravitational waveforms are essential for unbiased and precise estimation of source parameters. Recently developed surrogate models based on high-accuracy numerical relativity (NR) simulations are ideal for constraining physical parameters of heavy black hole merger events. In this paper, we first demonstrate the viability of these multi-modal surrogates as reliable parameter estimation tools. We show that NR surrogates can extract additional information from GW data that is inaccessible to traditional models, by analyzing a set of synthetic signals with the NR surrogate and other approximants. We also consider the case of two of the earliest binary black holes detected by the LIGO observatories: GW150914 and GW170104. We reanalyze their data with fully-precessing NR-surrogate templates and freely provide the resulting posterior samples as supplemental material. We find that our refined analysis is able to extract information from sub-dominant GW harmonics in data, and therefore better resolve the degeneracy in measuring source luminosity distance and orbital inclination for both events. We estimate the sources of both events to be 20-25% further away than was previously estimated. Our analyses also constrain their orbital orientation more tightly around face-on or face-off configurations than before. Additionally, for GW150914 we constrain the effective inspiral spin more tightly around zero. This work is one of the first to unambiguously extract sub-dominant GW mode information from real events. It is also a first step toward eliminating the approximations used in semi-analytic waveform models from GW parameter estimation. It also motivates that NR surrogates be extended to cover more of the binary black hole parameter space.
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We present the comparison of the analytical microscopic spectral density for lattice QCD with $N_{rm f}=2$ twisted mass fermions with the one obtained on the lattice utilizing configurations produced by the ETM collaboration. We extract estimates for the chiral condensate as well as the low-energy constant $W_8$ of Wilson $chi$-PT by employing spectral information of the Wilson Dirac operator with fixed index at finite volume.
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