A Comparative Analysis of the Supernova Legacy Survey Sample with {\Lambda}CDM and the Rh=ctR_{\rm h}=ct Universe

The use of Type~Ia SNe has thus far produced the most reliable measurement of the expansion history of the Universe, suggesting that $\Lambda$CDM offers the best explanation for the redshift--luminosity distribution observed in these events. But the analysis of other kinds of source, such as cosmic chronometers, gamma ray bursts, and high-$z$ quasars, conflicts with this conclusion, indicating instead that the constant expansion rate implied by the $R_{\rm h}=ct$ Universe is a better fit to the data. The central difficulty with the use of Type~Ia SNe as standard candles is that one must optimize three or four nuisance parameters characterizing supernova luminosities simultaneously with the parameters of an expansion model. Hence in comparing competing models, one must reduce the data independently for each. We carry~out such a comparison of $\Lambda$CDM and the $R_{\rm h}=ct$ Universe, using the Supernova Legacy Survey (SNLS) sample of 252 SN~events, and show that each model fits its individually reduced data very well. But since $R_{\rm h}=ct$ has only one free parameter (the Hubble constant), it follows from a standard model selection technique that it is to be preferred over $\Lambda$CDM, the minimalist version of which has three (the Hubble constant, the scaled matter density and either the spatial curvature constant or the dark-energy equation-of-state parameter). We estimate by the Bayes Information Criterion that in a pairwise comparison, the likelihood of $R_{\rm h}=ct$ is $\sim 90\%$, compared with only $\sim 10\%$ for a minimalist form of $\Lambda$CDM, in which dark energy is simply a cosmological constant. Compared to $R_{\rm h}=ct$, versions of the standard model with more elaborate parametrizations of dark energy are judged to be even less likely.Comment: 31 Pages, 5 Figures, 1 Table. Accepted for publication in A

Semiparametric Inference and Lower Bounds for Real Elliptically Symmetric Distributions

This paper has a twofold goal. The first aim is to provide a deeper understanding of the family of the Real Elliptically Symmetric (RES) distributions by investigating their intrinsic semiparametric nature. The second aim is to derive a semiparametric lower bound for the estimation of the parametric component of the model. The RES distributions represent a semiparametric model where the parametric part is given by the mean vector and by the scatter matrix while the non-parametric, infinite-dimensional, part is represented by the density generator. Since, in practical applications, we are often interested only in the estimation of the parametric component, the density generator can be considered as nuisance. The first part of the paper is dedicated to conveniently place the RES distributions in the framework of the semiparametric group models. The second part of the paper, building on the mathematical tools previously introduced, the Constrained Semiparametric Cram\'{e}r-Rao Bound (CSCRB) for the estimation of the mean vector and of the constrained scatter matrix of a RES distributed random vector is introduced. The CSCRB provides a lower bound on the Mean Squared Error (MSE) of any robust $M$-estimator of mean vector and scatter matrix when no a-priori information on the density generator is available. A closed form expression for the CSCRB is derived. Finally, in simulations, we assess the statistical efficiency of the Tyler's and Huber's scatter matrix $M$-estimators with respect to the CSCRB.Comment: This paper has been accepted for publication in IEEE Transactions on Signal Processin

A Magnetic Dynamo Origin For The Sub-mm Excess In Sgr A*

The sub-mm bump observed in the spectrum of Sgr A* appears to indicate the existence of a compact emitting component within several Schwarzschild radii, $r_S$, of the nucleus at the Galactic Center. This is interesting in view of the predicted circularized flow within $\sim 5-10 r_S$, based on detailed multi-dimensional hydrodynamic simulations of Bondi-Hoyle accretion onto this unusual object. In this paper, we examine the physics of magnetic field generation by a Keplerian dynamo subject to the conditions pertaining to Sgr A*, and show that the sub-mm bump can be produced by thermal synchrotron emission in this inner region. This spectral feature may therefore be taken as indirect evidence for the existence of this circularization. In addition, the self-Comptonization of the sub-mm bump appears to produce an X-ray flux exceeding that due to bremsstrahlung from this region, which may account for the X-ray counterpart to Sgr A* discovered recently by {\it Chandra}. However, the required accretion rate in the Keplerian flow is orders of magnitude smaller than that predicted by the Bondi-Hoyle simulations. We speculate that rapid evaporation, in the form of a wind, may ensue from the heating associated with turbulent mixing of gas elements with large eccentricity as they settle down into a more or less circular (i.e., low eccentricity) trajectory. The spectrum of Sgr A* longward of $\sim 1-2$ mm may be generated outside of the Keplerian flow, where the gas is making a transition from a quasi-spherical infall into a circularized pattern.Comment: 40 pages, 9 figure

Pharmacokinetic profiles of the active metamizole metabolites in healthy horses

Metamizole (MT) is an analgesic and antipyretic drug labelled for use in humans, horses, cattle, swine and dogs. MT is rapidly hydrolysed to the active primary metabolite 4-methylaminoantipyrine (MAA). MAA is formed in much larger amounts compared with other minor metabolites. Among other secondary metabolites, 4-aminoantipyrine (AA) is also relatively active. The aim of this research was to evaluate the pharmacokinetic profiles of MAA and AA after dose of 25 mg/kg MT by intravenous (i.v.) and intramuscular (i.m.) routes in healthy horses. Six horses were randomly allocated to two equally sized treatment groups according to a 2 9 2 crossover study design. Blood was collected at predetermined times within 24 h, and plasma was analysed by a validated HPLC-UV method. No behavioural changes or alterations in health parameters were observed in the i.v. or i.m. groups of animals during or after (up to 7 days) drug administration. Plasma concentrations of MAA after i.v. and i.m. administrations of MT were detectable from 5 min to 10 h in all the horses. Plasma concentrations of AA were detectable in the same range of time, but in smaller amounts. Maximum concentration (Cmax), time to maximum concentration (Tmax) and AUMC0-last of MAA were statistically different between the i.v. and i.m. groups. The AUCIM/AUCIV ratio of MAA was 1.06. In contrast, AUC0-last of AA was statistically different between the groups (P < 0.05) with an AUCIM/AUCIV ratio of 0.54. This study suggested that the differences in the MAA and AA plasma concentrations found after i.m. and i.v. administrations of MT might have minor consequences on the pharmacodynamics of the drug

Long-Term Radio Modulation in Sagittarius A* from Spin-Induced Disk Precession

There is some evidence, though yet unconfirmed, that Sagittarius A*--the supermassive black hole at the Galactic center--emits its radio waves modulated with a ~100-day period. What is intriguing about this apparent quasi-periodicity is that, though the amplitude of the modulation increases with decreasing wavelength (from 3.6 to 1.3 cm), the quasi-period itself does not seem to depend on the frequency of the radiation. It is difficult to imagine how a binary companion, were that the cause of this modulation, could have escaped detection until now. Instead, it has been suggested that the spin-induced precession of a disk surrounding a slowly rotating black hole could have the right period to account for this behavior. In this paper, we examine how Sagittarius A*'s light curve could be modulated by this mechanism. We demonstrate that the partial occultation of a nonthermal halo by a compact, radio-opaque disk does indeed produce the observed frequency-dependent amplitude. This appears to be in line with other observational arguments suggesting that Sagittarius A*'s mm/sub-mm spectrum is produced by a ~10 Schwarzschild-radius disk, whereas its cm-waves originate from a nonthermal particle distribution in a halo extending out to over 20 Schwarzschild radii. Interestingly, this model suggests that the observed period corresponds to half the precession period and that a non-axisymmetric disk could produce a second period roughly twice as long as the first.Comment: 17 pages, 5 figures, accepted to Ap

An Accretion-Induced X-ray Flare in Sgr A*

The recent detection of a three-hour X-ray flare from Sgr A* by Chandra provides very strong evidence for a compact emitting region near this supermassive black hole at the Galactic center. Sgr A*'s mm/sub-mm spectrum and polarimetric properties, and its quiescent-state X-ray flux density, are consistent with a model in which low angular momentum gas captured at large radii circularizes to form a hot, magnetized Keplerian flow within tens of Schwarzschild radii of the black hole's event horizon. In Sgr A*'s quiescent state, the X-ray emission appears to be produced by self-Comptonization (SSC) of the mm/sub-mm synchrotron photons emitted in this region. In this paper, we show that the prominent X-ray flare seen in Sgr A* may be due to a sudden enhancement of accretion through the circularized flow. Depending on whether the associated response of the anomalous viscosity is to increase or decrease in tandem with this additional injection of mass, the X-ray photons during the outburst may be produced either via thermal bremsstrahlung (if the viscosity decreases), or via SSC (if the viscosity increases). However, the latter predicts a softer X-ray spectrum than was seen by Chandra, so it appears that a bremsstrahlung origin for the X-ray outburst is favored. A strong correlation is expected between the mm/sub-mm and X-ray fluxes when the flare X-rays are produced by SSC, while the correlated variability is strongest between the sub-mm/far-IR and X-rays when bremsstrahlung emission is dominant during the flare. In addition, we shows that future coordinated multi-wavelength observations planned for the 2002 and 2003 cycles may be able to distinguish between the accretion and jet scenarios.Comment: 15 pages, 3 figures, To appear in ApJ Lette