A Study of Transient Very-High-Energy Gamma-Ray Emission from Gamma-Ray Bursts and Supernovae with H.E.S.S.

Gamma-ray bursts (GRBs) and supernovae (SNe) are well known examples of celestial transient events. Their tremendous energy release provides the ability to accelerate particles to the highest energies. The High Energy Stereoscopic System (H.E.S.S.) is an array of four imaging atmospheric Cherenkov telescopes, covering gamma-ray energies between 100 GeV and 100 TeV (VHE range). In this work the H.E.S.S. data on GRBs are searched for VHE gamma-ray emission. Amongst them is the analysis of GRB 100621A, the brightest X-ray source so far detected by the Swift satellite. Measurements at lower energies make it a promising candidate within the sensitivity reach of the H.E.S.S. instrument, however no indication of VHE emission is found. The derived upper limits constrain the existence of additional spectral components and provide important input for understanding the emission process. Furthermore, H.E.S.S. pointing positions are compared to a recently created, unified SN catalogue in order to identify extragalactic SNe accidentally in the field of view during the observation of other targets. The analysis reveals no significant detection, which allows one to constrain possible VHE emission scenarios. This work also includes a technical discussion of the H.E.S.S. telescope pointing accuracy. A new approach, the SingleCCD concept, is discussed and evaluated, which is interesting for the next generation of imaging atmospheric Cherenkov telescopes

Search of extended or delayed TeV emission from GRBs with HAWC

Gamma-ray bursts (GRBs) are among the most luminous sources in the universe and the nature of their emission up to very high energy is one of the most important open issue connected with the study of these peculiar events. The High Altitude Water Cherenkov (HAWC) gamma-ray observatory, installed at an altitude of 4100 m a. s. l. in the state of Puebla (Mexico), has completed its second year of full operations. Thanks to its instantaneous field of view of ~2 sr and its high duty cycle ($\ge$ 95%), HAWC is an ideal instrument for the study of transient phenomena such as GRBs. We performed a search for TeV emission delayed with respect to, and of longer duration than the prompt emission observed by satellites. We present here the results obtained by observing at the position of a sample of GRBs detected by the Fermi and Swift satellites from December 2014 to February 2017. The upper limits resulting from this analysis are presented and theoretical implications are discussed.Comment: Presented at the 35th International Cosmic Ray Conference (ICRC2017), Bexco, Busan, Korea. See arXiv:1708.02572 for all HAWC contribution

The Bacterial Defensin Resistance Protein MprF Consists of Separable Domains for Lipid Lysinylation and Antimicrobial Peptide Repulsion

Many bacterial pathogens achieve resistance to defensin-like cationic antimicrobial peptides (CAMPs) by the multiple peptide resistance factor (MprF) protein. MprF plays a crucial role in Staphylococcus aureus virulence and it is involved in resistance to the CAMP-like antibiotic daptomycin. MprF is a large membrane protein that modifies the anionic phospholipid phosphatidylglycerol with l-lysine, thereby diminishing the bacterial affinity for CAMPs. Its widespread occurrence recommends MprF as a target for novel antimicrobials, although the mode of action of MprF has remained incompletely understood. We demonstrate that the hydrophilic C-terminal domain and six of the fourteen proposed trans-membrane segments of MprF are sufficient for full-level lysyl-phosphatidylglycerol (Lys-PG) production and that several conserved amino acid positions in MprF are indispensable for Lys-PG production. Notably, Lys-PG production did not lead to efficient CAMP resistance and most of the Lys-PG remained in the inner leaflet of the cytoplasmic membrane when the large N-terminal hydrophobic domain of MprF was absent, indicating a crucial role of this protein part. The N-terminal domain alone did not confer CAMP resistance or repulsion of the cationic test protein cytochrome c. However, when the N-terminal domain was coexpressed with the Lys-PG synthase domain either in one protein or as two separate proteins, full-level CAMP resistance was achieved. Moreover, only coexpression of the two domains led to efficient Lys-PG translocation to the outer leaflet of the membrane and to full-level cytochrome c repulsion, indicating that the N-terminal domain facilitates the flipping of Lys-PG. Thus, MprF represents a new class of lipid-biosynthetic enzymes with two separable functional domains that synthesize Lys-PG and facilitate Lys-PG translocation. Our study unravels crucial details on the molecular basis of an important bacterial immune evasion mechanism and it may help to employ MprF as a target for new anti-virulence drugs

Measurement of the

The r-process has been shown to be robust in reproducing the abundance distributions of heavy elements, such as europium, seen in ultra-metal poor stars. In contrast, observations of elements 26 < Z < 47 display overabundances relative to r-process model predictions. A proposed additional source of early nucleosynthesis is the weak r-process in neutrino-driven winds of core-collapse supernovae. It has been shown that in this site (α,n) reactions are both crucial to nucleosynthesis and the main source of uncertainty in model-based abundance predictions. Aiming to improve the certainty of nucleosynthesis predictions, the cross section of the important reaction 86Kr(α,n)89Sr has been measured at an energy relevant to the weak r-process. This experiment was conducted in inverse kinematics at TRIUMF with the EMMA recoil mass spectrometer and the TIGRESS gamma-ray spectrometer. A novel type of solid helium target was used

Gammapy - A prototype for the CTA science tools

International audienceGammapy is a Python package for high-level gamma-ray data analysis built on Numpy, Scipy and Astropy. It enables to analyse gamma-ray data and to create sky images, spectra and lightcurves, from event lists and instrument response information, as to determine the position, morphology and spectra of gamma-ray sources.So far Gammapy has mostly been used to analyse data from H.E.S.S. and Fermi-LAT, and is now being used for the simulation and analysis of observations from the Cherenkov Telescope Array (CTA). We have proposed Gammapy as a prototype for the CTA science tools. This contribution gives an overview of the Gammapy package and shows an analysis application example with simulated CTA data

GammapyVersion 0.19

Gammapy is a community-developed, open-source Python package for gamma-ray astronomy built on Numpy, Scipy and Astropy. It is the core library for the CTA science tools and can also be used to analyse data from existing imaging atmospheric Cherenkov telescopes (IACTs), such as H.E.S.S., MAGIC and VERITAS. It also provides some support for Fermi-LAT and HAWC data analysis