Hard X‐ray polarimetry of solar flares with BATSE

We describe a technique for measuring the polarization of hard X‐rays from solar flares based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Since the albedo component can represent a relatively large fraction (up to 40%) of the direct source flux, there will generally be sufficient signal for making such a measurement. The sensitivity of this approach is therefore dictated by the effective area and the ability of a detector system to ‘image’ the albedo flux. The 4π coverage of the BATSE detectors on the Compton Gamma‐RayObservatory provides an opportunity to measure both the direct and the albedo flux from a given solar flare event. Although the BATSE design (with its large field‐of‐view for each detector) is not optimized for albedo polarimetry, we have nonetheless investigated the feasibility of this technique using BATSE data

Using BATSE to measure gamma-ray burst polarization

We describe a technique for measuring the polarization of hard x-rays from γ-ray bursts based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Although the BATSE design (with its large field-of-view for each detector) is not optimized for albedo polarimetry, we have nonetheless investigated the feasibility of this technique using BATSE data

Response of carrot roots to wounding stress induced by processing: changes in chemical composition and enzyme activity.

In the present work both whole carrot roots and Cenouretes® from the cultivars Esplanada and Sugar Snax 54, were stored for 17 days at 5 ± 1.5 °C under dark or light conditions and evaluated after 2, 5, 8, 11, 14 and 17 days of storage

Resistivity study of the pseudogap phase for (Hg,Re) - 1223 superconductors

The pseudogap phase above the critical temperature of high $T_{c}$ superconductors (HTSC) presents different energy scales and it is currently a matter of intense study. The complexity of the HTSC normal state requires very accurate measurements with the purpose of distinguishing different types of phenomena. Here we have performed systematically studies through electrical resistivity ($\rho$) measurements by several different current densities in order to obtain an optimal current for each sample. This approach allows to determine reliable values of the pseudogap temperature $T^{*}(n)$, the layer coupling temperature between the superconductor layers $T_{LD}(n)$, the fluctuation temperature $T_{scf}(n)$ and the critical temperature $T_{c}(n)$ as function of the doping $n$. The interpretation of these different temperature scales allows to characterize possible scenarios for the (Hg,Re) - 1223 normal state. This method, described in detail here, and used to derive the (Hg,Re)-1223 phase diagram is general and can be applied to any HTSC.Comment: 31 pages, 12 figures, Latex; 25 pages, LaTeX; 11 figures; rewrited section II and III; added 18 reference; rewrited title, added discussion sectio

Search for weakly interacting sub-eV particles with the OSQAR laser-based experiment: results and perspectives

Recent theoretical and experimental studies highlight the possibility of new fundamental particle physics beyond the Standard Model that can be probed by sub-eV energy experiments. The OSQAR photon regeneration experiment looks for "Light Shining through a Wall" (LSW) from the quantum oscillation of optical photons into "Weakly Interacting Sub-eV Particles" (WISPs), like axion or axion-like particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of $2 \times 14.3$ m. No excess of events has been detected over the background. The di-photon couplings of possible new light scalar and pseudo-scalar particles can be constrained in the massless limit to be less than $8.0\times10^{-8}$ GeV$^{-1}$. These results are very close to the most stringent laboratory constraints obtained for the coupling of ALPs to two photons. Plans for further improving the sensitivity of the OSQAR experiment are presented.Comment: 7 pages, 7 figure

Moody's Correlated Binomial Default Distributions for Inhomogeneous Portfolios

This paper generalizes Moody's correlated binomial default distribution for homogeneous (exchangeable) credit portfolio, which is introduced by Witt, to the case of inhomogeneous portfolios. As inhomogeneous portfolios, we consider two cases. In the first case, we treat a portfolio whose assets have uniform default correlation and non-uniform default probabilities. We obtain the default probability distribution and study the effect of the inhomogeneity on it. The second case corresponds to a portfolio with inhomogeneous default correlation. Assets are categorized in several different sectors and the inter-sector and intra-sector correlations are not the same. We construct the joint default probabilities and obtain the default probability distribution. We show that as the number of assets in each sector decreases, inter-sector correlation becomes more important than intra-sector correlation. We study the maximum values of the inter-sector default correlation. Our generalization method can be applied to any correlated binomial default distribution model which has explicit relations to the conditional default probabilities or conditional default correlations, e.g. Credit Risk${}^{+}$, implied default distributions. We also compare some popular CDO pricing models from the viewpoint of the range of the implied tranche correlation.Comment: 29 pages, 17 figures and 1 tabl

Low temperature structural phase transition and incommensurate lattice modulation in the spin gap compound BaCuSi2O6

Results of high resolution x-ray diffraction experiments are presented for single crystals of the spin gap compound BaCuSi$_2$O$_6$ in the temperature range from 16 to 300 K. The data show clear evidence of a transition from the room temperature tetragonal phase into an incommensurately modulated orthorhombic structure below $\sim$100 K. This lattice modulation is characterized by a resolution limited wave vector {\bf q}$_{IC}$=(0,$\sim$0.13,0) and its 2$^{nd}$ and 3$^{rd}$ harmonics. The phase transition is first order and exhibits considerable hysteresis. This observation implies that the spin Hamiltonian representing the system is more complex than originally thought.Comment: 4 pages, 4 figure

XTE J1946+274 = GRO J1944+26: An Enigmatic Be/X-ray Binary

XTE J1946+274 = GRO J1944+26 is a 15.8 s Be/X-ray pulsar discovered simultaneously in 1998 September with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) and the All-Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE). Here we present new results from BATSE and {\em RXTE} including a pulse timing analysis, spectral analysis, and evidence for an accretion disk. Our pulse timing analysis yielded an orbital period of 169.2 days, a moderate eccentricity of 0.33, and implied a mass function of 9.7 M_sun. We observed evidence for an accretion disk, a correlation between measured spin-up rate and flux, which was fitted to obtain a distance estimate of 9.5 +/- 2.9 kpc. XTE J1946+274 remained active from 1998 September - 2001 July, undergoing 13 outbursts that were not locked in orbital phase. Comparing RXTE PCA observations from the initial bright outburst in 1998 and the last pair of outbursts in 2001, we found energy and intensity dependent pulse profile variations in both outbursts and hardening spectra with increasing intensity during the fainter 2001 outbursts. In 2001 July, optical Halpha observations indicate a density perturbation appeared in the Be disk as the X-ray outbursts ceased. We propose that the equatorial plane of the Be star is inclined with respect to the orbital plane in this system and that this inclination may be a factor in the unusual outburst behavior of the system.Comment: 18 pages, 15 figures, To appear in ApJ v584, Feb 20, 2003 issu

SiO Outflows in the Most Luminous and Massive Protostellar Sources of the Southern Sky

(Abridged) High-mass star formation is far less understood than low-mass star formation. It entails molecular outflows, which disturb the protostellar clump. Studying these outflows and the shocked gas they cause is key for a better understanding of this process. This study aims to characterise the behaviour of molecular outflows in the most massive protostellar sources in the Southern Galaxy by looking for evolutionary trends and associating shocked gas with outflow activity. We present APEX SEPIA180 observations (beamwidth $\sim$36") of SiO outflow candidates of a sample of 32 luminous and dense clumps, candidates to harbouring Hot Molecular Cores. We study the SiO(4-3) line emission, an unambiguous tracer of shocked gas and recent outflow activity, the HCO$^+$(2-1) and H$^{13}$CO$^+$(2-1) lines. 78% of our sample present SiO emission. Nine of these also have wings in the HCO$^+$ line, indicating outflow activity. The SiO emission of these 9 sources is more intense and wider than the rest, suggesting that the outflows in this group are faster and more energetic. Three positive correlations between the outflow properties were found, which suggest that more energetic outflows bear to mobilise more material. No correlation was found between the evolutionary stage indicator $L/M$ and SiO outflow properties, supporting that outflows happen throughout the whole high-mass star formation process. We conclude that sources with both SiO emission and HCO$^+$ wings and sources with only SiO emission are in virtually the same advanced stage of evolution in the high-mass star formation process. The former present more massive and more powerful SiO outflows than the latter. Thus, looking for more outflow signatures such as HCO$^+$ wings could help identify more massive and active massive star-forming regions in samples of similarly evolved sources, as well as sources with older outflow activity.Comment: 24 pages, 37 figures, 11 table