8102056
An Energetic Afterglow from a Distant Stellar Explosion
We present the discovery of radio afterglow emission from the high-redshift (z = 6.295) burst GRB 050904. The peak flux density for this burst is similar to typical low-redshift gamma-ray bursts (GRBs). We further show that beyond a redshift of order unity, the flux densities of radio afterglows are largely insensitive to redshift, consistent with predictions. By combining the existing X-ray, near-infrared, and radio measurements, we derive estimates for the kinetic energy and opening angle of the blast wave and for the density of the circumburst medium into which it expands. Both the kinetic and radiated energy indicate that GRB 050904 was an unusually energetic burst (10^52 ergs). More importantly, we are able to make an in situ measurement of the density structure of the circumburst medium. We conclude that GRB 050904 exploded into a constant-density medium with n0 = 680 cm^−3, which is 2 orders of magnitude above the nominal value for low-redshift GRBs. The next generation of centimeter (EVLA) and millimeter radio instruments (ALMA) will be able to routinely detect events such as GRB 050904 and use them to study magnetic fields and the atomic and molecular gas in the high-redshift universe.
113407190
A THEORETICAL COLOR-VELOCITY CORRELATION FOR SUPERNOVAE ASSOCIATED WITH GAMMA-RAY BURSTS
We carry out the first multi-dimensional radiative transfer calculations to simultaneously compute synthetic spectra and light curves for models of supernovae driven by fast bipolar outflows. These allow us to make self-consistent predictions for the orientation dependence of both color evolution and spectral features. We compare models with different degrees of asphericity and metallicity and find significant observable consequences of both. In aspherical models, we find spectral and light curve features that vary systematically with observer orientation. In particular, we find that the early-phase light curves are brighter and bluer when viewed close to the polar axis but that the peak flux is highest for equatorial (off-axis) inclinations. Spectral line features also depend systematically on observer orientation, including the velocity of the Si II 6355 A line. Consequently, our models predict a correlation between line velocity and color that could assist the identification of supernovae associated with off-axis jet-driven explosions. The amplitude and range of this correlation depends on the degree of asphericity, the metallicity, and the epoch of observation but we find that it is always present and acts in the same direction.
5990408
The Science Case for PILOT I: Summary and Overview
PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed 2.5-m optical/infrared telescope to be located at Dome C on the Antarctic plateau. Conditions at Dome C are known to be exceptional for astronomy. The seeing (above ∼30 m height), coherence time, and isoplanatic angle are all twice as good as at typical mid-latitude sites, while the water-vapour column, and the atmosphere and telescope thermal emission are all an order of magnitude better. These conditions enable a unique scientific capability for PILOT, which is addressed in this series of papers. The current paper presents an overview of the optical and instrumentation suite for PILOT and its expected performance, a summary of the key science goals and observational approach for the facility, a discussion of the synergies between the science goals for PILOT and other telescopes, and a discussion of the future of Antarctic astronomy. Paper II and Paper III present details of the science projects divided, respectively, between the distant Universe (i.e. studies of first light, and the assembly and evolution of structure) and the nearby Universe (i.e. studies of Local Group galaxies, the Milky Way, and the Solar System).
13255925
The Mount Stromlo A bell Cluster Supernova Search
We have initiated a 3 year project to find supernovae in a well-defined sample of high-density southern Abell clusters with redshifts z ≤ 0.08. These observations will provide a volume-limited sample of Type Ia supernovae (SNe Ia) to more than a magnitude below their peak brightness and will enable us to (1) measure the luminosity function of SNe, (2) further explore the correlation of light-curve shape with the absolute luminosity of SNe Ia to better understand SNe Ia as distance indicators, (3) measure SN rates, (4) measure the bulk motion of the Local Group using SNe Ia, and (5) directly compare SN Ia distances with brightest cluster galaxy distances. We use the MACHO wide-field two-color imager on the 1.3 m telescope at Mount Stromlo to routinely monitor ~12 clusters per week. We describe our technique for target selection and scheduling search observations, and for finding and identifying SN candidates. We also describe the results from the first year of our program, including the detection of 19 SNe, several RR Lyrae variables, and hundreds of asteroids.
118556930
HATS-1b: The First Transiting Planet Discovered by the HATSouth Survey
We report the discovery of HATS-1b, a transiting extrasolar planet orbiting the moderately bright V = 12.05 G dwarf star GSC 6652-00186, and the first planet discovered by HATSouth, a global network of autonomous wide-field telescopes. HATS-1b has a period of P 3.4465 days, mass of Mp 1.86 M J, and radius of Rp 1.30 R J. The host star has a mass of 0.99 M ☉ and radius of 1.04 R ☉. The discovery light curve of HATS-1b has near-continuous coverage over several multi-day timespans, demonstrating the power of using a global network of telescopes to discover transiting planets.
3943345
First Searches for Optical Counterparts to Gravitational-wave Candidate Events
During the Laser Interferometer Gravitational-wave Observatory and Virgo joint science runs in 2009-2010, gravitational wave (GW) data from three interferometer detectors were analyzed within minutes to select GW candidate events and infer their apparent sky positions. Target coordinates were transmitted to several telescopes for follow-up observations aimed at the detection of an associated optical transient. Images were obtained for eight such GW candidates. We present the methods used to analyze the image data as well as the transient search results. No optical transient was identified with a convincing association with any of these candidates, and none of the GW triggers showed strong evidence for being astrophysical in nature. We compare the sensitivities of these observations to several model light curves from possible sources of interest, and discuss prospects for future joint GW-optical observations of this type.
73663027
Gas gain uniformity tests performed on multiwire proportional chambers for the LHCb muon system
We present the experimental setup and the results of the gas gain uniformity tests performed as part of the quality control of the multiwire proportional chambers produced at CERN for the LHCb muon system. The test provides a relative gas gain measurement over the whole chamber sensitive area. It is based on the analysis of the pulse height spectrum obtained when the chamber is exposed to a 241 Am radioactive source. Since the measurement is normalized to the peak of a precise pulse generator, the gain uniformity can also be evaluated among different gas gaps and different chambers. In order to cope with the specific requirements related to the relatively high number of chambers and to their varying geometry, a standalone and compact data acquisition system has been developed which is programmable at the hardware level and may be applied to many other applications requiring precise time-to-digital and analog-to-digital conversion, in correlated or non-correlated mode. r 2008 Elsevier B.V. All rights reserved. PACS: 06.60.Mr; 07.05.Hd; 29.30.Kv; 29.40.Cs
56449268
Time-Resolved Electron Beam Phase Space Tomography at a Soft X-Ray Free-Electron Laser
High-gain free-electron lasers (FELs) in the ultraviolet and x-ray regime put stringent demands on the peak current, transverse emittance, and energy spread of the driving electron beam. At the soft x-ray FEL FLASH, a transverse deflecting microwave structure (TDS) has been installed to determine these parameters for the longitudinally compressed bunches, which are characterized by a narrow leading peak of high charge density and a long tail. The rapidly varying electromagnetic field in the TDS deflects the electrons vertically and transforms the time profile into a streak on an observation screen. The bunch current profile was measured single shot with an unprecedented resolution of 27 fs under FEL operating conditions. A precise single-shot measurement of the energy distribution along a bunch was accomplished by using the TDS in combination with an energy spectrometer. Variation of quadrupole strengths allowed for a determination of the horizontal emittance as a function of the longitudinal position within a bunch, the so-called slice emittance. In the bunch tail, a normalized slice emittance of about $2\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ was found, in agreement with expectations. In the leading spike, however, surprisingly large emittance values were observed, in apparent contradiction with the low emittance deduced from the measured FEL gain. By applying three-dimensional phase space tomography, we were able to show that the bunch head contains a central core of low emittance and high local current density, which is presumably the lasing part of the bunch.
121591364
Electron motion in counting gases — New answers and new questions
Abstract An experimental method is described which allows the simultaneous measurement of drift velocity, longitudinal and transverse diffusion coefficients of electrons in counting gas mixtures. Results in CF 4 and argon/CF 4 are presented. In CH 4 and Ar/CH 4 mixtures the problems in the calculation of the transverse diffusion in molecular gases are discussed. An empirical formula which can be used for practical purposes has been derived. A comparison with recently published theoretical results suggests that a multiterm Boltzmann code could be the adequate formalism to calculate the motion of electrons in counting gas mixtures.
118504484
Final results of the EDELWEISS-II WIMP search using a 4-kg array of cryogenic germanium detectors with interleaved electrodes
Abstract The EDELWEISS-II Collaboration has completed a direct search for WIMP dark matter with an array of ten 400-g cryogenic germanium detectors in operation at the Laboratoire Souterrain de Modane. The combined use of thermal phonon sensors and charge collection electrodes with an interleaved geometry enables the efficient rejection of γ -induced radioactivity as well as near-surface interactions. A total effective exposure of 384 kg d has been achieved, mostly coming from fourteen months of continuous operation. Five nuclear recoil candidates are observed above 20 keV, while the estimated background is 3.0 events. The result is interpreted in terms of limits on the cross-section of spin-independent interactions of WIMPs and nucleons. A cross-section of 4.4 × 10 − 8 pb is excluded at 90%CL for a WIMP mass of 85 GeV. New constraints are also set on models where the WIMP-nucleon scattering is inelastic.
120535624
Precision measurements of magnetic deflection angles and drift velocities in crossed electric and magnetic fields
Abstract An experiment is described that allows to measure the magnetic deflection angle α and the drift velocity w in crossed electric and magnetic fields for arbitrary gas mixtures. The method covers about two orders of magnitude in the reduced electric field, magnetic fields up to 1 T and tan α up to 4.5. An unprecedented accuracy for w and tan α of about ± 1% including systematic uncertainties could be achieved. Results of measurements in pure methane, argon with 10% methane and krypton with 5% methane are presented and discussed.