Characterizing the dead time of the ECLAIRs camera on board the mission SVOM

French (CNES) and Chinese (CNSA) space agencies collaborate to build the SVOM (Space-based multi-band Variable Object Monitor) mission due to be launched in 2021 to study gamma-ray bursts and high-energy transients. The SVOM prime instrument, ECLAIRs, will detect and localize GRBs autonomously as well as provide a spectral and temporal characterization of the GRB prompt emission. ECLAIRs is expected to detect around 200 GRBs during the 3 year nominal lifetime of the mission. ECLAIRs is a wide-field (\(\sim 2 \text {sr}\)) coded mask camera with a detection plane made of 8 independent sectors of 800 Schottky CdTe detectors working in the 4-150 keV energy range. Each sector is connected to independent readout electronics. In this paper, we focus on the study of the temporal performance and we estimate how dead time will affect bright transient lightcurves. We discuss the analytical model based on simulations over a large range of source count rates on a dedicated test bench. We show that dead time will not significantly affect ECLAIRs data, even for the brightest GRBs (3.7% of lost counts for a count rate of 10⁵ counts.s^??1 over the detection plane in the energy range 4?150 keV) and our model can nicely correct the parts of the lightcurves which are the most affected by dead time effects for very bright GRBs.     

The two basic components of the interstellar neutral hydrogen and its relation with the galactic structure

The two basic components of the neutral hydrogen, cool dense clouds merged in a hotter tenuous medium, are studied using 21 cm absorption data of the Parkes Survey. The mean parameters obtained for the typical clouds next to the galactic plane are τ_p = 1.7, velocity half-width=3.3 km s^?1. Their temperatures areT _sc ≥40 K with a meanT _sc =63±12 K and the obtained hot gas density isn _HH=(0.15±0.05) atom cm^?3. Theoretical analysis following Giovanelli and Brown (1973) reveals that the pressure equilibrium condition (n _HH+2n _e )·T _SH≈n _HC·T _sc is compatible with the quoted values if it is assumed that the cosmic abundances in the interstellar medium are below the adopted normal solar abundance. This lack of heavy elements suggests accretion to grains which is consistent with the observed narrow concentration of the dark matter on the galactic layer (≤100 pc halfwidth). The same pressure condition leads to a mean cool cloud density ofn _HC～30 atom cm^?3 and a hot gas temperature ofT _SH～10 500 K. Comparison with data from Hii regions suggests that the cool clouds are somewhat denser and less extensive than such regions. An explanation for it is the expansion that the Hii regions went through in their origin. Comparison with 21 cm emission data shows that the cloud galactic layer is only about a quarter as thick as the hot gas layer. All the present results suggest that only such clouds can be spatially related with the typical I population associated with the spiral structure.     

Angular momenta in binary systems

The correlations angular momentaL to massesM are studied for different types of spectroscopic binaries. The functionsL=AM ^b have the coefficientb with the values expected from a Keplerian mechanics, but the valuesA(q, T), A(q, a), A(q, v), associated tob=5/3, 3/2, and 2, respectively, are given (statistically speaking) by multiples or submultiples of discrete values of: the mass ratiosq, the semi-major axesa, periodsT, and velocitiesv of the reduced mass. This indicates the existence of a discrete unit of actionL=(1/2)×potential energy xperiod. Postulates about equivalent states of angular momenta for different orbital parameters are introduced, being this coherent with the analysis of the up-to-date data. Among other examples of the application of such equivalence postulates, we haveL(M) (W-type of the WUMa systems)L(M) (main group of the Algol binaries). The quantum units of action seen here are equivalent to those seen in the solar system in one of our previous works. From comparisons with galaxies and single stars, it is evidence that there is not an unique universal functionL=AM ^b, when the fine structure of the relation is analysed: each type of object has its own coefficients,A, b. It sems to be that there are an upper and a lower limit for all the possible functions. The upper limit isL=A _gM^5/3, withA _g1 associated to periodsT Hubble time, and the lower limit isL=GM ^2/c, with 1. The existence of the upper limit can be investigated with studies of pairs of galaxies, and the lower limit can be tested with analysis of single G, K, M stars. The quantical hypothesis introduced here can be checked definitely, when available larger samples of data with low errors, with similar quality as the selected list of almost 80 eclipsing binaries (mainly detached systems) analysed here.     

Properties of theβ pictoris disc deduced from optical imaging polarimetry

The asymmetries in the brightness structure and levels of polarization between the two sides of the Pic disc are discussed. The possibility of these differences being caused by a planet, or planets, within the circumstellar disc is investigated.     

The spiral structure in the inner parts of the Galaxy

The spiral structure of the inner parts of the Galaxy is studied using 21 cm line data and stellar data. To study the neutral hydrogen distribution in the galactic layer a parameter =(dV/dr) proportional to the mean densities is calculated using a first approximation for the velocity gradients due to differential rotation.The obtained distribution (R, Z) shows spiral features completely consistent with the early star distribution and with the Hii regions. The corrugation effect of the galactic layer is observed in all the studied zones in neutral hydrogen and in the distribution of the OB stars in the Carina zone.The pattern obtained indicates four spiral arms for the inner parts of the Galaxy, three of which are identified also in the stellar data (arms -I, -II, and -III) and the more distant -IV in Hii regions.The local arm according to the stellar data of Kilkennyet al. forms a feature completely similar to the arms -I and -II and there are no indications that this arm is a special material branch between two main spiral arms as has been supposed in order to conciliate the neutral hydrogen pattern with the stellar distribution.The pitch angles for the spiral arms are approximately 13°–17°.The observed wave form distribution of the hydrogen cloud layer is completely consistent with the theoretical predictions of Nelson (1976) but there are no indications of such an effect in the intercloud hydrogen. The corrugated cloud layer has a width of 100 pc, a wave amplitude of 70 pc, and a wavelength which grows with the galactic center distance (approx. 2 kpc in the zones next to the galactic nucleus and 2.6–3.0 kpc in the zones next to the Sun). To each wavelength correspond two spiral arms. The spiral features in our Galaxy show characteristics quite similar to the features in the Andromeda nebula, not only in the component materials (neutral hydrogen, Hii regions and possibly also dust and stars) but also in their kinematics.     

Fingerprinting TCE in a bedrock aquifer using compound-specific isotope analysis

A dual isotope approach based on compound-specific isotope analysis (CSIA) of carbon (C) and chlorine (Cl) was used to identify sources of persistent trichloroethylene (TCE) that caused the shut-down in 1994 of a municipal well in an extensive fractured dolostone aquifer beneath Guelph, Ontario. Several nearby industrial properties have known subsurface TCE contamination; however, only one has created a comprehensive monitoring network in the bedrock. The impacted municipal well and many monitoring wells were sampled for volatile organic compounds (VOCs), inorganic parameters, and CSIA. A wide range in isotope values was observed at the study site. The TCE varies between -35.6‰ and -21.8‰ and from 1.6‰ to 3.2‰ for δ(13) C and δ(37) Cl, respectively. In case of cis-1,2-dichloroethene, the isotope values range between -36.3‰ and -18.9‰ and from 2.4‰ to 4.7‰ for δ(13) C and δ(37) Cl, respectively. The dual isotope approach represented by a plot of δ(13) C vs. δ(37) Cl shows the municipal well samples grouped in a domain clearly separate from all other samples from the property with the comprehensive well network. The CSIA results collected under non-pumping and short-term pumping conditions thus indicate that this particular property, which has been studied intensively for several years, is not a substantial contributor of the TCE presently in the municipal well under non-pumping conditions. This case study demonstrates that CSIA signatures would have been useful much earlier in the quest to examine sources of the TCE in the municipal well if bedrock monitoring wells had been located at several depths beneath each of the potential TCE-contributing properties. Moreover, the CSIA results show that microbial reductive dechlorination of TCE occurs in some parts of the bedrock aquifer. At this site, the use of CSIA for C and Cl in combination with analyses of VOC and redox parameters proved to be important due to the complexity introduced by biodegradation in the complex fractured rock aquifer. It is highly recommended to revisit the study when the municipal well is back into full operation.