Scientific prospects for spectroscopy of the gamma-ray burst prompt emission with SVOM

SVOM (Space-based multi-band astronomical Variable Objects Monitor) is a Sino-French space mission dedicated to the study of Gamma-Ray Bursts (GRBs) in the next decade, capable to detect and localise the GRB emission, and to follow its evolution in the high-energy and X-ray domains, and in the visible and NIR bands. The satellite carries two wide-field high-energy instruments: a coded-mask gamma-ray imager (ECLAIRs; 4–150 keV), and a gamma-ray spectrometer (GRM; 15–5500 keV) that, together, will characterise the GRB prompt emission spectrum over a wide energy range. In this paper we describe the performances of the ECLAIRs and GRM system with different populations of GRBs from existing catalogues, from the classical ones to those with a possible thermal component superimposed to their non-thermal emission. The combination of ECLAIRs and the GRM will provide new insights also on other GRB properties, as for example the spectral characterisation of the subclass of short GRBs showing an extended emission after the initial spike.     

A statistical analysis applied to the Rf/φ method

A statistical analysis for the R_f/φ method is developed in the paper. The technique provides estimates of R_s, R_i and θ according to R_f and φ. Moreover, we can restore the pattern of initial orientations of marker objects by means of their frequency histogram, provided the strain is homogeneous. It is unnecessary to postulate random initial orientations if the principal directions of strain ellipsoid are known.     

“Extreme boiling” model for variable salinity of the Hokko low-sulfidation epithermal Au prospect, southwestern Hokkaido, Japan

The Hokko prospect is located in the Minamikayabe area southwestern Hokkaido, Japan, where gold-bearing quartz veins of Pliocene age are exposed at the surface. The alteration mineral assemblage is typical of low-sulfidation epithermal systems, with the quartz veins associated with adularia alteration overprinted on Late Miocene propylitic alteration. Fluid inclusion studies of the vein quartz reveal mean homogenization temperatures of approximately 220 °C, and the co-existence of low-salinity (<2 wt.% NaCl equivalent) and moderate salinity (2 to 12 wt.% NaCl equivalent) fluid inclusions within the same veins. The moderate salinity fluid inclusions (2–12 wt.% NaCl equivalent) typically have relatively low homogenization temperatures between 150° to 200 °C. The results obtained from stable isotope analysis of  δ¹⁸O in quartz vein material showed a gradual decrease in  δ¹⁸O signatures with increasing depth. The majority of the samples have calculated fluid source signatures (δ¹⁸O_H2O) between −8.0 and −10.0‰, but there is a significant change in the composition above 185 m drill depth. The shallower samples in particular show a wide range of oxygen isotope signatures that are associated with the moderate salinity fluid inclusions. We interpret that low-salinity inclusions within the Hokko system represent the composition of the liquid phase of the fluid, before boiling, and that the moderate-salinity inclusions are representative of the residual liquid phase, after extensive non-adiabatic boiling and vapor loss in an open system. This mechanism resulted in the entrapment of fluids with variable salinities at the same time, and in close proximity to each other. This is also reflected in the  δ¹⁸O_H2O values which become more variable and heavier where the moderate-salinity inclusions occur. Deposition of ore minerals within the Hokko vein system also occurred at this time as a result of boiling and gas loss. Received: 30 May 1997 / Accepted: 6 January 1998     

Biofilms, microbial mats and microbe-particle interactions: electron microscope observations from diatomaceous sediments

Sediments and diatoms from the mudflats of the Bay of Bourgneuf in western France were examined in an electron microscope study of biofilms and microbial mats. The sediments were kept in an aquarium for study and a diatom culture was made of the benthic diatoms. The sediment biofilm was composed of exopolymeric substances (EPS), incorporated clay particles and, rarely, bacteria. This film coated all particles at the sediment-water interface. Its surface morphology reflected its composition and internal structure. Thin films were smooth, whilst a lumpy structure or incorporated fibrils produced either a mammillated or ropy surface, and clays in the structure gave rise to a flaky morphology. At shallow depths in the sediment column (0.5 cm) the biofilm was already degraded. The biofilm coating degraded diatom frustules in the benthic diatom culture consisted of EPS and bacteria and presented a ragged appearance. Microbial mats occurred on the surface of the fresh littoral sediments as well as those in the aquarium, and on the wall of the aquarium. The mat on the surface of the aquarium sediments had an open structure with webs of fibrils and bacteria in the pore space. It formed in a relatively quiet environment. Pore space was more limited in the mat from the surface of the fresh littoral sediments, in which direct contact between biofilm coated particles was common. In the exposed environment of the aquarium wall there was a thick, resistant coating of EPS. In addition to binding particles together, the presence of mats and biofilms in sediments affects sediment physical properties such as porosity and permeability, the flux of dissolved substances in pore waters and the dissolution of particles and can, therefore, influence early diagenesis. Mats and biofilms seem to be more readily preserved in the geological record than the micro-organisms, such as bacteria, which produce them. Their identification in the sedimentary record would greatly aid interpretation of sediment genesis and evaluation of the microbial role in sediment formation.     

Forward-Modeling of Doppler Shifts in EUV Spectral Lines

The interpretation of red- and blueshifts in EUV spectral observations remains a challenge that could provide important clues to the heating processes in the solar atmosphere. Hinode/EUV Imaging Spectrometer (EIS) observations near the footpoints of coronal loops show blueshifts for emission lines with temperatures above 1 MK and redshifts for lines below 1 MK. The implications are addressed through numerical modeling of loop dynamics. The simulation results are converted into synthetic EIS observations. A single one-dimensional loop cannot reproduce the observed behavior. However, persistent red- and blueshifts can be understood as a collective spectral signature of a bundle of 10 or more loops that have an average temperature of around 1 MK and evolve in a similar way: small-scale heating events occur randomly along each loop on a timescale of several minutes. Strong blueshifts are accompanied by low intensities. The power-law index of the energy distribution has a minor role in determining the average Doppler shifts.     

Emission curve of growth for Feii in chromospheric limb spectra

The 270 chromospheric emission lines of Feii ranging between 2000 and 3200 Å observed by Skylab at a height of 4 (2900 km) above the limb of the quiet Sun are analyzed by the emission curve of growth method, using newly calculated gf-values. It is derived that the excitation temperature is 7.2 × 10³ K and that the turbulent velocity is consistent with the previous results that the microturbulent velocity is lower than 10 km s^–1 in the cool (<10⁴ K) region of the chromosphere.Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 270.     

Infrared Study of T Tauri Stars Based on IRAS and 2MASS Observations

The IRAS and 2MASS associations for 193 T Tauri stars are identified in this paper. From the color–color diagrams and spectral index, it is found that the IR excesses for most samples are due to thermal emission from the circumstellar material, as suggested previously. It is also found that the IR excesses at IRAS region for few T Tauri stars and the near-IR excesses for some T Tauri stars are likely attributed to free-free emission or free-bound emission from the circumstellar ionized gas. Moreover, It is found in deredened J–H versus H–K color–color diagram that there is a slight separation in different spectral groups. The T Tauri stars locus equation in J–H versus H–K color–color diagram for our sample is also presented.     

The bottom magnetic field and magnetosphere evolution of neutron star in low-mass X-ray binary

The accretion-induced neutron star (NS) magnetic field evolution is studied through considering the accretion flow to drag the field lines aside and dilute the polar-field strength, and as a result the equatorial field strength increases, which is buried inside the crust on account of the accretion-induced global compression of star crust. The main conclusions of model are as follows: (i) the polar field decays with increase in the accreted mass; (ii) the bottom magnetic field strength of about 10⁸ G can occur when the NS magnetosphere radius approaches the star radius, and it depends on the accretion rate as     ; and (iii) the NS magnetosphere radius decreases with accretion until it reaches the star radius, and its evolution is little influenced by the initial field and the accretion rate after accreting  ∼0.01 M_⊙  , which implies that the magnetosphere radii of NSs in low-mass X-ray binaries would be homogeneous if they accreted the comparable masses. As an extension, the physical effects of the possible strong magnetic zone in the X-ray NSs and recycled pulsars are discussed. Moreover, the strong magnetic fields in the binary pulsars PSR 1831−00 and PSR 1718−19 after accreting about  0.5 M_⊙  in the binary-accretion phase,  8.7 × 10¹⁰  and  1.28 × 10¹² G  , respectively, can be explained through considering the incomplete frozen flow in the polar zone. As an expectation of the model, the existence of the low magnetic field  (∼3 × 10⁷ G)  NSs or millisecond pulsars is suggested.