116977941
A glimpse of the end of the dark ages: the gamma-ray burst of 23 April 2009 at redshift 8.3
It is thought that the first generations of massive stars in the Universe were an important, and quite possibly dominant, source of the ultra-violet radiation that reionized the hydrogen gas in the intergalactic medium (IGM); a state in which it has remained to the present day. Measurements of cosmic microwave background anisotropies suggest that this phase-change largely took place in the redshift range z=10.8 +/- 1.4, while observations of quasars and Lyman-alpha galaxies have shown that the process was essentially completed by z=6. However, the detailed history of reionization, and characteristics of the stars and proto-galaxies that drove it, remain unknown. Further progress in understanding requires direct observations of the sources of ultra-violet radiation in the era of reionization, and mapping the evolution of the neutral hydrogen fraction through time. The detection of galaxies at such redshifts is highly challenging, due to their intrinsic faintness and high luminosity distance, whilst bright quasars appear to be rare beyond z~7. Here we report the discovery of a gamma-ray burst, GRB 090423, at redshift z=8.26 -0.08 +0.07. This is well beyond the redshift of the most distant spectroscopically confirmed galaxy (z=6.96) and quasar (z=6.43). It establishes that massive stars were being produced, and dying as GRBs, ~625 million years after the Big Bang. In addition, the accurate position of the burst pinpoints the location of the most distant galaxy known to date. Larger samples of GRBs beyond z~7 will constrain the evolving rate of star formation in the early universe, while rapid spectroscopy of their afterglows will allow direct exploration of the progress of reionization with cosmic time.
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).
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.
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.
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.
49382390
MEASUREMENT AND STABILIZATION OF THE BUNCH ARRIVAL TIME AT FLASH
To fully exploit the experimental opportunities offered by the 10 − 30 fs long light pulses from FLASH, e.g. in pump-probe experiments, precise measurements and control of the electron-bunch arrival-time on the 10 fs scale are needed. A bunch arrival time monitor which uses the optical synchronization system of FLASH as a reference has been developed for this purpose. The bunch-induced signal from a GHz-bandwidth beam pick-up is guided into an electro-optical modulator in which the periodic laser pulse train of the optical synchronization system experiences an amplitude modulation. Detection of this modulation allows to determine the bunch arrival time with a resolution of better than 10 fs. The superconducting linac of FLASH generates trains of up to 800 bunches. The signals from the bunch arrival time monitor can be used for an intrabunch train feedback stabilizing the arrival time to 40 fs (rms). The feedback is capable of generating well-defined arrival time patterns within a bunch train which are useful for overlap-scans in pump-probe experiments. First results from the feedback installed at FLASH will be presented.
58891676
Constraints on Photon Pulse Duration from Longitudinal Electron Beam Diagnostics at a Soft X-Ray Free-Electron Laser.
The successful operation of X-ray free-electron lasers (FELs), like the Linac Coherent Light Source or the Free-Electron Laser in Hamburg (FLASH), makes unprecedented research on matter at atomic length and ultrafast time scales possible. However, in order to take advantage of these unique light sources and to meet the strict requirements of many experiments in photon science, FEL photon pulse durations need to be known and tunable. This can be achieved by controlling the FEL driving electron beams, and high-resolution longitudinal electron beam diagnostics can be utilized to provide constraints on the expected FEL photon pulse durations. In this paper, we present comparative measurements of soft X-ray pulse durations and electron bunch lengths at FLASH. The soft X-ray pulse durations were measured by FEL radiation pulse energy statistics and compared to electron bunch lengths determined by frequency-domain spectroscopy of coherent transition radiation in the terahertz range and time-domain longitudinal phase space measurements. The experimental results, theoretical considerations, and simulations show that high-resolution longitudinal electron beam diagnostics provide reasonable constraints on the expected FEL photon pulse durations. In addition, we demonstrated the generation of soft X-ray pulses with durations below 50 fs (FWHM) after the implementation of the new uniform electron bunch compression scheme used at FLASH.
2664921
Test Station for the CARIOCA FE-chip of the LHCb Muon Detector
This document describes the hardware and the software of a Front-End Electronics Test Station developed to test and characterize the Front-End ASIC for the LHCb Muon chambers. This ASIC, an 8-channel amplifier, shaper and discriminator with baseline restoration, processes read-out signals generated by Multi-Wire Proportional and GEM chambers located in a high radiation environment. It is almost entirely analog. In total, an amount of about 25000 chips will be produced in both the engineering and production runs. They will require individual testing, before final assembly on printed circuit boards. The test system we present has the following features: variable and bipolar charge injection, custom read-out, rate and time measuring circuitry, power consumption control, data analysis and statistical tools. The system is controlled by a LabVIEW based program. We present the results of about 3000 tests of ASIC produced in the engineering run.
119650160
MICROSTRIP GAS CHAMBERS : RECENT DEVELOPMENTS, RADIATION DAMAGE AND LONG-TERM BEHAVIOR
Abstract In the past years the technology of Microstrip Gas Chambers (MSGC) has made considerable progress offering a variety of possible new applications in various fields of research. MSGC are used to detect neutrons, X-rays, synchrotron radiation and VUV light as well as the full range of ionizing particles in nuclear and high energy physics. A variety of systematic studies led to a considerable increase in understanding of the functional principle and limiting parameters of the MSGC technology and enabled improved performances. In view of the large (HERA-B) and very large (CMS) detector systems planning to use MSGC in intense hadronic particle fluxes, the question of radiation hardness and long-term stability is of special importance. The problem of micro discharges, induced by heavy ionizing particles and destroying the electrode structure, turned out to be a major limitation to the applicability of MSGC in hadronic beams and demanded for new and revised solutions. The present status and future perspectives of the various technologies are discussed.
19130398
Status of the optical replica synthesizer at FLASH
A novel laser-based method to measure the longitudinal profile of ultrashort electron bunches,known as the Optical Replica Synthesizer (ORS) [1] is currently implemented at the free-electron laser FLASH at DESY. The paper describes its technical layout and the status of the project.