Dark Energy Survey Year 1 results: galaxy clustering for combined probes

We measure the clustering of DES Year 1 galaxies that are intended to be combined with weak lensing samples in order to produce precise cosmological constraints from the joint analysis of large-scale structure and lensing correlations. Two-point correlation functions are measured for a sample of 6.6×10 5 luminous red galaxies selected using the \textsc{redMaGiC} algorithm over an area of 1321 square degrees, in the redshift range 0.15 0.5 , b(z =0.68)=1.93±0.05 for L/L ∗ > 1 and b(z =0.83)=1.99±0.07 for L/L ∗ >1.5 , broadly consistent with expectations for the redshift and luminosity dependence of the bias of red galaxies. We show these measurements to be consistent with the linear bias obtained from tangential shear measurements

Multi-messenger Observations of a Binary Neutron Star Merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ∼ 1.7 {{s}} with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of {40}-8+8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 {M}ȯ . An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ∼ 40 {{Mpc}}) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ∼ 9 and ∼ 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.</p

Accelerator Module Repair for the European XFEL Installation

International audienceRepair actions of different extent have been performed at 61 modules of the 100 accelerating series modules for the European XFEL to qualify them for the tunnel installation. Four modules could not be repaired in time. CEA Saclay managed to perform three major repairs in parallel to the series module integration, the residual repair actions took place at DESY Hamburg. In this paper we will give an overview on the various technical problems which required being fixed before the tunnel installation and on the repair actions performed

Cleanroom Assembly of the LIPAc Cryomodule

International audienceIn complement to the development activities for fusion reactors (JT-60SA & ITER), Fusion for Energy contributes to the R&D for material characterisation facilities. LIPAc is the technical demonstrator for the production and acceleration of a D⁺ beam that will be used for neutron production by nuclear stripping reaction on a liquid Li target. Since its first beam in 2014, the LIPAc construction and commissioning continues and will be concluded with the cryomodule installation, aiming for beam validation at nominal power. The cryomodule assembly, started in March 2019, was paused due to welding issues on the solenoid bellows. The slow pumping group used for the cleanroom assembly also needed improvement to overcome helium contamination. Two and half years were devoted to the pumping improvement and, repair, cold tests and high pressure rinsing of the solenoids. In August 2022, the cleanroom assembly resumed with the mounting of all power couplers to the SRF cavities. Despite good progress, the assembly had to be paused again to fix leaks on different vacuum components and a solenoid BPM port. This paper presents the issues faced and their solutions along the cold mass assembly