Explore the vast range of titles available.

Searching for as yet undetected γ-ray sources is one of the main stated goals of the Fermi Large Area Telescope Collaboration. In this paper, we explore the capability of a filtering method based on a finite mixture of von Mises–Fisher distributions. The proposed procedure is specifically designed to handle data with support on the unit sphere. The assumption of a parametric model for each high energy emitting source allows us to derive an explicit expression for both the direction of the sources and their angular resolutions. The corresponding measures are based on the directional mean and the quantiles of the single mixture components. Sound criteria of model selection can provide an automatic way to determine the number of detected sources. Additionally, a likelihood-ratio test is developed to evaluate their significance. The procedure is tested on simulated data sets of photon emissions from high energy sources within the energy range [10−1,000] GeV. A real data example consisting of a sample of the Fermi LAT data collected over a period of about 7.2 years within the energy range [10−1,000] GeV, in a subregion of the γ-ray sky, is furthermore provided.

In the first 3.5 years of operations, Fermi detected several sources whose flaring activity brought them to exceed daily fluxes brighter than F ( E > 100MeV) > 10 −6 ph cm −2 s −1 . These episodes were promptly reported to the scientific community by the Fermi collaboration by means of astronomer telegrams (ATels). We focus our attention on the sample composed by these flaring sources, most of which are blazars, known to be extremely variable over the whole electromagnetic spectrum, from radio to γ-ray energies. We study properties of the selected sample and compare them to general characteristics of the Fermi source catalogue.

The Fermi LAT provides a continuous and uniform monitoring of the Universe in the gamma-ray band. During the first year many gamma-ray blazar flares, some unidentified transients and emission by the Sun while in a quiet state were promptly detected. This is mainly due to the design of the mission, featuring a detector, the LAT with a wide field of view, and to the operation of the spacecraft itself, that can cover every region of the sky every 3 hours. Nevertheless, the scientific exploitation of this monitoring is more fruitful when early information about transients reaches a broader community. In this respect, the indefatigable activity of flare advocates, who worked on weekly shifts to validate the results and quickly broadcast information about flares and new detections, was the key to most scientific results.

The most identified sources observed by Fermi/LAT are blazars, based on which we can investigate the emission mechanisms and beaming effect in the γ -ray bands for blazars. Here, we used the compiled around 450 Fermi blazars with the available X-ray observations to estimate their Doppler factors and compared them with the integral γ -ray luminosity in the range of 1–100 GeV. It is interesting that the integral γ -ray luminosity is closely correlated with the estimated Doppler factor, log ν γ L ν γ = ( 2.95 ± 0.09 ) log δ + 43.59 ± 0.08 for the whole sample. When the dependence of the correlation between them and the X-ray luminosity is removed, the correlation is still strong, which suggests that the γ -ray emissions are strongly beamed.

Interest in parallel architectures applied to real time selections is growing in High Energy Physics (HEP) experiments. In this paper we describe performance measurements of Graphic Processing Units (GPUs) and Intel Many Integrated Core architecture (MIC) when applied to a typical HEP online task: the selection of events based on the trajectories of charged particles. We use as benchmark a scaled-up version of the algorithm used at CDF experiment at Tevatron for online track reconstruction – the SVT algorithm – as a realistic test-case for low-latency trigger systems using new computing architectures for LHC experiment. We examine the complexity/performance trade-off in porting existing serial algorithms to many-core devices. Measurements of both data processing and data transfer latency are shown, considering different I/O strategies to/from the parallel devices.

The origin of Galactic cosmic rays is a century-long puzzle. Indirect evidence points to their acceleration by supernova Shockwaves, but we know little of their escape from the shock and their evolution through the turbulent medium surrounding massive stars. Gamma rays can probe their spreading through the ambient gas and radiation fields. The Fermi Large Area Telescope (LAT) has observed the star-forming region of Cygnus X. The 1-to 100-gigaelectronvolt images reveal a 50-parsec-wide cocoon of freshly accelerated cosmic rays that flood the cavities carved by the stellar winds and ionization fronts from young stellar clusters. It provides an example to study the youth of cosmic rays in a superbubble environment before they merge into the older Galactic population.

In this talk, we will show the beaming effect for Fermi/LAT blazars, then we discuss the correlations between γ-ray luminosity and other parameters, such as radio Doppler factors, superluminal motions, and core-dominance parameters. We also compare the Doppler factors determined from the γ-ray luminosity, X-ray emissions, and the short-term time scales with those from other methods. Our discussions suggest that γ-ray emissions may be strongly beamed.

Relativistic jets around supermassive black holes (SMBHs) are well-known powerful $\\gamma$-ray emitters. In absence of the jets in radio-quiet active galactic nuclei (AGNs), how the SMBHs work in $\\gamma$-ray bands is still unknown despite of great observational efforts made in the last 3 decades. Considering the previous efforts, we carefully select an AGN sample composed of 37 nearby Seyfert galaxies with ultra-hard X-rays for the goals of $\\gamma$-ray detections by excluding all potential contamination in this band. Adopting a stacking technique, here we report the significant $\\gamma$-ray detection (${\\rm TS}=30.6$, or $5.2\\,\\sigma$) from the sample using 15-year Fermi-Large Area Telescope (LAT) observation. We find an average $\\gamma$-ray luminosity of the sample as $(1.5\\pm1.0)\\times10^{40}{\\,\\rm erg\\,s^{-1}}$ at energies from 1-300 GeV. Limited by the well-known pair production from the interaction of $\\gamma$-rays with low energy photons, $\\gtrsim$ several GeV $\\gamma$-rays are found to originate from an extended corona ($\\sim 2.7\\times 10^6\\,R_{\\rm g}$), whereas the canonical much more compact X-ray corona ($\\sim 10\\,R_{\\rm g}$) is responsible for 1 to several GeV $\\gamma$-rays. The finding of the compact region lends to strong supports to the long-time theoretical expectations, but the extended corona is beyond all the existing models. One promising scenario is that the electron-positron pairs produced in the compact X-ray corona would expand as fireball, similar to that in $\\gamma$-ray bursts, forming the structure of extended corona.

Issue Title: Special Issue: Proceedings of the International Conference on Variability of Blazars: From Jansky to Fermi (VBJF) In the first 3.5 years of operations, Fermi detected several sources whose flaring activity brought them to exceed daily fluxes brighter than F(E > 100MeV) > 10^sup -6^ ph cm^sup -2^ s^sup -1^. These episodes were promptly reported to the scientific community by the Fermi collaboration by means of astronomer telegrams (ATels). We focus our attention on the sample composed by these flaring sources, most of which are blazars, known to be extremely variable over the whole electromagnetic spectrum, from radio to γ-ray energies. We study properties of the selected sample and compare them to general characteristics of the Fermi source catalogue.

Globular clusters are compact groups of hundreds of thousands to millions of stars. About 200 are known to orbit our Galaxy; a few are known to emit γ-rays. This emission is thought to originate from the population of millisecond pulsars that inhabits these clusters; however, these pulsars have only been detected at radio wavelengths. Freire et al. (p. 1107, published online 3 November) report the detection of an individual pulsar in a globular cluster at γ-ray wavelengths and show that the cluster's γ-ray emission is dominated by that single pulsar. This pulsar is much more luminous than previously detected millisecond pulsars, suggesting that it is the youngest yet to be detected. We report on the Fermi Large Area Telescope's detection of γ-ray (>100 mega-electron volts) pulsations from pulsar J1823-3021A in the globular cluster NGC 6624 with high significance (∼7 σ). Its γ-ray luminosity, Lγ = (8.4 ± 1.6) × 1034 ergs per second, is the highest observed for any millisecond pulsar (MSP) to date, and it accounts for most of the cluster emission. The nondetection of the cluster in the off-pulse phase implies that it contains <32 γ-ray MSPs, not ∼100 as previously estimated. The γ-ray luminosity indicates that the unusually large rate of change of its period is caused by its intrinsic spin-down. This implies that J1823-3021A has the largest magnetic field and is the youngest MSP ever detected and that such anomalous objects might be forming at rates comparable to those of the more normal MSPs. [PUBLICATION ABSTRACT]