Search results for "Gamma-ray"
showing 10 items of 374 documents
A next generation Ultra-Fast Flash Observatory (UFFO-100) for IR/optical observations of the rise phase of gamma-ray bursts
2012
The Swift Gamma-ray Burst (GRB) observatory responds to GRB triggers with optical observations in ~ 100 s, but cannot respond faster than ~ 60 s. While some ground-based telescopes respond quickly, the number of sub-60 s detections remains small. In mid- to late-2013, the Ultra-Fast Flash Observatory-Pathfinder is to be launched on the Lomonosov spacecraft to investigate early optical GRB emission. This pathfinder mission is necessarily limited in sensitivity and event rate; here we discuss a next generation rapid-response space observatory. We list science topics motivating our instruments, those that require rapid optical-IR GRB response, including: A survey of GRB rise shapes/times, meas…
Gravitational Waves from the Papaloizou-Pringle Instability in Black-Hole-Torus Systems
2011
Black hole (BH)--torus systems are promising candidates for the central engine of gamma-ray bursts (GRBs), and also possible outcomes of the collapse of supermassive stars to supermassive black holes (SMBHs). By three-dimensional general relativistic numerical simulations, we show that an $m=1$ nonaxisymmetric instability grows for a wide range of self-gravitating tori orbiting BHs. The resulting nonaxisymmetric structure persists for a timescale much longer than the dynamical one, becoming a strong emitter of large amplitude, quasiperiodic gravitational waves. Our results indicate that both, the central engine of GRBs and newly formed SMBHs, can be strong gravitational wave sources observa…
Enhanced detection of terrestrial gamma-ray flashes by AGILE
2015
Abstract At the end of March 2015 the onboard software configuration of the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite was modified in order to disable the veto signal of the anticoincidence shield for the minicalorimeter instrument. The motivation for such a change was the understanding that the dead time induced by the anticoincidence prevented the detection of a large fraction of Terrestrial Gamma‐Ray Flashes (TGFs). The configuration change was highly successful resulting in an increase of one order of magnitude in TGF detection rate. As expected, the largest fraction of the new events has short duration (<100 μs), and part of them has simultaneous association with light…
High-energy γ-ray detection of supernova remnants in the Large Magellanic Cloud
2022
We present the results of a cluster search in the gamma-ray sky images of the Large Magellanic Cloud (LMC) region by means of the Minimum Spanning Tree (MST) and DBSCAN algorithms, at energies higher than 6 and 10 GeV, using 12 years of Fermi-LAT data. Several significant clusters were found, the majority of which associated with previously known gamma-ray sources. We confirm our previous detection of the Supernova Remnants N 49B and N 63A and found new significant clusters associated with the SNRs N 49, N 186D and N 44. These sources are among the brightest X-ray remnants in the LMC and corresponds to core-collapse supernovae interacting with dense HII regions, indicating that an hadronic …
Universal transport dynamics in a quenched tunnel-coupled Luttinger liquid
2016
The transport dynamics of a quenched Luttinger liquid tunnel-coupled to a fermionic reservoir is investigated. In the transient dynamics, we show that for a sudden quench of the electron interaction universal power-law decay in time of the tunneling current occurs, ascribed to the presence of entangled compound excitations created by the quench. In sharp contrast to the usual non universal power-law behavior of a zero-temperature non-quenched Luttinger liquid, the steady state tunneling current is ohmic and can be explained in terms of an effective quench-activated heating of the system. Our study unveils an unconventional dynamics for a quenched Luttinger liquid that could be identified in…
Single molecules probe local density of modes (LDOS) around photonic nanostructures
2008
International audience; According to Fermi's golden rule, the fluorescence decay rate is directly proportional to the projected local density of photonic modes (LDOS) at the molecule location. The relevant LDOS depends on the molecule orientation. In this paper, the direct measurement of the fluorescence lifetime near gold dot photonic structures is investigated and compared to calculated LDOS. Detailed analysis of the decay channels is presented on the basis of numerical simulations.
Panel Discussion on Data Analysis Trends in X-Ray and Gamma-Ray Astronomy
1986
ZIMMERMANN: Let me begin the panel discussion on Data Analysis Trends in X-ray and Gamma-ray astronomy by first introducing the panel members. These are from the left to the right: Roland Diehl, Ethan Schreier, Rosolino Buccheri, Livio Scarsi, Jean-Marc Chassery and Wolfgang Voges. With the exception of Jean-Marc Chassery, who is an expert on image processing and statistical analysis, all the others have longer experience in the X-ray and Gamma-ray fields. May I ask the speakers to keep their contributions to not more than five minutes, in order to allow ample room for discussion with the audience.
Highlights from the ARGO-YBJ Experiment
2012
""The ARGO-YBJ experiment at YangBaJing in Tibet (4300m a.s.l.) has been taking data with its full layout since October 2007. Here we present a few significant results obtained in gamma-ray astronomy and cosmic-ray physics. Emphasis is placed on the analysis of gamma-ray emission from point-like sources (Crab Nebula, MRK 421), on the preliminary limit on the antiproton\\\/proton flux ratio, on the large-scale cosmic-ray anisotropy and on the proton-air cross-section. The performance of the detector is also discussed, and the perspectives of the experiment are outlined.""
Conservative upper limits on WIMP annihilation cross section from Fermi-LAT $γ$-rays
2011
The spectrum of an isotropic extragalactic {\gamma}-ray background (EGB) has been measured by the Fermi-LAT telescope at high latitudes. Two new models for the EGB are derived from the subraction of unresolved point sources and extragalactic diffuse processes, which could explain from 30% to 70% of the Fermi-LAT EGB. Within the hypothesis that the two residual EGBs are entirely due to the annihilation of dark matter (DM) particles in the Galactic halo, we obtain stringent upper limits on their annihilation cross section. Severe bounds on a possible Sommerfeld enhancement of the annihilation cross section are set as well. Finally, we consider models for DM annihilation depending on the inver…
Shell-Structure and Pairing Interaction in Superheavy Nuclei: Rotational Properties of the Z=104 Nucleus (256)Rf
2012
The rotational band structure of the Z ¼ 104 nucleus 256Rf has been observed up to a tentative spin of 20@ using state-of-the-art -ray spectroscopic techniques. This represents the first such measurement in a superheavy nucleus whose stability is entirely derived from the shell-correction energy. The observed rotational properties are compared to those of neighboring nuclei and it is shown that the kinematic and dynamic moments of inertia are sensitive to the underlying single-particle shell structure and the specific location of high-j orbitals. The moments of inertia therefore provide a sensitive test of shell structure and pairing in superheavy nuclei which is essential to ensure the val…