Challenging GRB models through the broadband dataset of GRB060908

Context: Multiwavelength observations of gamma-ray burst prompt and afterglow emission are a key tool to disentangle the various possible emission processes and scenarios proposed to interpret the complex gamma-ray burst phenomenology. Aims: We collected a large dataset on GRB060908 in order to carry out a comprehensive analysis of the prompt emission as well as the early and late afterglow. Methods: Data from Swift-BAT, -XRT and -UVOT together with data from a number of different ground-based optical/NIR and millimeter telescopes allowed us to follow the afterglow evolution from about a minute from the high-energy event down to the host galaxy limit. We discuss the physical parameters required to model these emissions. Results: The prompt emission of GRB060908 was characterized by two main periods of activity, spaced by a few seconds of low intensity, with a tight correlation between activity and spectral hardness. Observations of the afterglow began less than one minute after the high-energy event, when it was already in a decaying phase, and it was characterized by a rather flat optical/NIR spectrum which can be interpreted as due to a hard energy-distribution of the emitting electrons. On the other hand, the X-ray spectrum of the afterglow could be fit by a rather soft electron distribution. Conclusions: GRB060908 is a good example of a gamma-ray burst with a rich multi-wavelength set of observations. The availability of this dataset, built thanks to the joint efforts of many different teams, allowed us to carry out stringent tests for various interpretative scenarios showing that a satisfactorily modeling of this event is challenging. In the future, similar efforts will enable us to obtain optical/NIR coverage comparable in quality and quantity to the X-ray data for more events, therefore opening new avenues to progress gamma-ray burst research.Comment: A&A, in press. 11 pages, 5 figure

ATLASGAL - Ammonia observations towards the southern Galactic Plane

Context: The initial conditions of molecular clumps in which high-mass stars form are poorly understood. In particular, a more detailed study of the earliest evolutionary phases is needed. The APEX Telescope Large Area Survey of the whole inner Galactic disk at 870 μm, ATLASGAL, has therefore been conducted to discover high-mass star-forming regions at different evolutionary phases. Aims: We derive properties such as velocities, rotational temperatures, column densities, and abundances of a large sample of southern ATLASGAL clumps in the fourth quadrant. Methods: Using the Parkes telescope, we observed the NH3 (1, 1) to (3, 3) inversion transitions towards 354 dust clumps detected by ATLASGAL within a Galactic longitude range between 300° and 359° and a latitude within ± 1.5°. For a subsample of 289 sources, the N2H+ (1–0) line was measured with the Mopra telescope. Results: We measured a median NH3 (1, 1) line width of ~ 2 km s-1, rotational temperatures from 12 to 28 K with a mean of 18 K, and source-averaged NH3 abundances from 1.6 × 10-6 to 10-8. For a subsample with detected NH3 (2, 2) hyperfine components, we found that the commonly used method to compute the (2, 2) optical depth from the (1, 1) optical depth and the (2, 2) to (1, 1) main beam brightness temperature ratio leads to an underestimation of the rotational temperature and column density. A larger median virial parameter of ~ 1 is determined using the broader N2H+ line width than is estimated from the NH3 line width of ~ 0.5 with a general trend of a decreasing virial parameter with increasing gas mass. We obtain a rising NH3 (1, 1)/N2H+ line-width ratio with increasing rotational temperature. Conclusions: A comparison of NH3 line parameters of ATLASGAL clumps to cores in nearby molecular clouds reveals smaller velocity dispersions in low-mass than high-mass star-forming regions and a warmer surrounding of ATLASGAL clumps than the surrounding of low-mass cores. The NH3 (1, 1) inversion transition of 49% of the sources shows hyperfine structure anomalies. The intensity ratio of the outer hyperfine structure lines with a median of 1.27 ± 0.03 and a standard deviation of 0.45 is significantly higher than 1, while the intensity ratios of the inner satellites with a median of 0.9 ± 0.02 and standard deviation of 0.3 and the sum of the inner and outer hyperfine components with a median of 1.06 ± 0.02 and standard deviation of 0.37 are closer to 1

Stereocontrolled alkylation of chiral pyridinium salt toward a short enantioselective access to 2-alkyl- and 2,6-dialkyl-1,2,5,6-tetrahydropyridines.

Treatment of salts 1a?b with Grignard reagents gives, after reduction of the resulting unstable dihydropyridines 7, the tetrahydropyridines 8a?c, with modest selectivities but in very few steps and under practical conditions. Higher stereoand regioselectivities are obtained with salt 1c which gives the tetrahydropyridines 15a?e. In addition, the dihydropyrid- Introduction The enantioselective synthesis of six-membered nitrogen heterocycles has been the subject of a large number of studies during the past few years due to the interest of these intermediates in natural alkaloid and medicinal chemistry. As a consequence, efficient methods are now available for preparing chiral 2- and 2,6-substituted piperidines.[1] However, few methods are available concerning the corresponding enantiopure substituted tetrahydropyridines.[2] Therefore, we now present a strategy which is briefly summarized in Scheme 1. The main features of this approach are: (a) selective alkylation with Grignard reagents[3?5] of pyridinium salts 1 (Scheme 1), now readily available from chiral primary amines;[6] (b) protonation of the resulting dihydropyridines 2 to give dihydropyridinium salt equivalents 3;[7] (c) additional treatment with a Grignard reagent affording the 2,6-disubstituted tetrahydropyridines 4. Scheme 1. General strategy for the enantioselective construction of substituted tetrahydropyridines The interest of this approach is illustrated by the short synthesis from salt 1c (Scheme 2) of (2)-lupetidin, (1)- solenopsin A and indolizidines (2)-5 and (2)-6, this last synthesis being designed as an example of further ring elaboration of the tetrahydropyridines 4. [a] Institut de Chimie des Substances Naturelles, C.N.R.S. Avenue de la Terrasse, 91198 Gif-Sur-Yvette CEDEX, France Fax: (internat.) 1 33-1/69077247 E-mail: [email protected] [b] Departamento de Quimica, ICEB, Universidad Federal de Ouro Preto, Campus Morro de Cruzeiro, 35400.00, Ouro Preto, MG, Brazil Eur. J. Org. Chem. 2000, 139121399 ? WILEY-VCH VerlagGmbH, D-69451Weinheim, 2000 14342193X/00/040821391 $ 17.501.50/0 1391 ine intermediates 11b cyclize to give the new oxazolidine derivatives 12a?e, which turn out to be good precursors of the 2,6-trans-disubstituted tetrahydropyridines 21a?e. Selective syntheses of (?)-lupetidin, (+)-solenopsin, and indolizidines (?)-5 and (?)-6 are presented as representative examples of applications