Abstract The Fermi All-sky Variability Analysis (FAVA) provides a photometric alternative for identifying week-long gamma-ray flares across the entire sky while being independent of any diffuse ...Galactic or isotropic emission model. We reviewed 779 weeks of Fermi Large Area Telescope data analyzed by FAVA to estimate the rate and origin of Galactic gamma-ray flares, and to search for new variable Galactic gamma-ray transients. We report an estimated yearly rate of ∼8.5 Galactic gamma-ray flares yr –1 , with ∼1 flare yr –1 coming from unknown sources. Out of the known gamma-ray sources that are spatially coincident with these detected flares, we report gamma-ray flares for six of them for the first time. All six are classified as pulsars, or a source of unknown nature but which positionally overlaps with known supernova remnants or pulsar wind nebulae (PWNe). This potentially means these sites are tentative candidates to be the second known site of a variable gamma-ray PWN, after the famous Crab Nebula’s PWN. Additionally, we identify nine unassociated flares that are unlikely to have originated from known gamma-ray sources.
GammaLib and ctools Knodlseder, J; Mayer, M; Deil, C ...
Astronomy and astrophysics (Berlin),
09/2016, Letnik:
593
Journal Article
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The field of gamma-ray astronomy has seen important progress during the last decade, yet to date no common software framework has been developed for the scientific analysis of gamma-ray telescope ...data. We propose to fill this gap by means of the GammaLib software, a generic library that we have developed to support the analysis of gamma-ray event data. GammaLib was written in C++ and all functionality is available in Python through an extension module. Based on this framework we have developed the ctools software package, a suite of software tools that enables flexible workflows to be built for the analysis of Imaging Air Cherenkov Telescope event data. The ctools are inspired by science analysis software available for existing high-energy astronomy instruments, and they follow the modular ftools model developed by the High Energy Astrophysics Science Archive Research Center. The ctools were written in Python and C++, and can be either used from the command line via shell scripts or directly from Python. In this paper we present the GammaLib and ctools software versions 1.0 that were released at the end of 2015. GammaLib and ctools are ready for the science analysis of Imaging Air Cherenkov Telescope event data, and also support the analysis of Fermi-LAT data and the exploitation of the COMPTEL legacy data archive. We propose using ctools as the science tools software for the Cherenkov Telescope Array Observatory.
The Large Area Telescope on board the Fermi satellite observed a gamma-ray flare in the Crab Nebula lasting for approximately nine days in April of 2011. The source, which at optical wavelengths has ...a size of approx =11 lt-yr across, doubled its gamma-ray flux within eight hours. The peak photon flux was (186 + or - 6) x 10 super(-7) cm super(-2) s super(-1) above 100 MeV, which corresponds to a 30-fold increase compared to the average value. During the flare, a new component emerged in the spectral energy distribution, which peaked at an energy of (375 + or - 26) MeV at flare maximum. The observations imply that the emission region was likely relativistically beamed toward us and that variations in its motion are responsible for the observed spectral variability.
Context. It has been suggested that the bow shocks of runaway stars are sources of high-energy gamma rays (E > 100 MeV). Theoretical models predicting high-energy gamma-ray emission from these ...sources were followed by the first detection of non-thermal radio emission from the bow shock of BD+43°3654 and non-thermal X-ray emission from the bow shock of AE Aurigae. Aims. We perform the first systematic search for MeV and GeV emission from 27 bow shocks of runaway stars using data collected by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. Methods. We analysed 57 months of Fermi-LAT data at the positions of 27 bow shocks of runaway stars extracted from the Extensive stellar BOw Shock Survey catalogue (E-BOSS). A likelihood analysis was performed to search for gamma-ray emission that is not compatible with diffuse background or emission from neighbouring sources and that could be associated with the bow shocks. Results. None of the bow shock candidates is detected significantly in the Fermi-LAT energy range. We therefore present upper limits on the high-energy emission in the energy range from 100 MeV to 300 GeV for 27 bow shocks of runaway stars in four energy bands. For the three cases where models of the high-energy emission are published we compare our upper limits to the modelled spectra. Our limits exclude the model predictions for ζ Ophiuchi by a factor ≈5.
We report on a bright flare in the Crab Nebula detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The period of significantly increased luminosity occurred in ...2013 March and lasted for approximately two weeks. During this period, we observed flux variability on timescales of approximately 5 hr. The combined photon flux above 100 MeV from the pulsar and its nebula reached a peak value of (12.5 + or - 0.8) times 10 super(-6) cm super(-2) s super(-1) on 2013 March 6. This value exceeds the average flux by almost a factor of six and implies a ~20 times higher flux for the synchrotron component of the nebula alone. This is the second brightest flare observed from this source. Spectral and temporal analysis of the LAT data collected during the outburst reveal a rapidly varying synchrotron component of the Crab Nebula while the pulsar emission remains constant in time.
Research linking bikeway infrastructure and cycling levels has increased significantly over the last 20 years - with the strongest growth since 2010. The research has evolved from the study of lanes ...and paths, to include analyses of the role of intersection treatments, and finally to studies that attempt to measure the whole bike network. Most studies suggest a positive relationship between bikeway networks or aspects of the network and cycling levels. Stated and revealed-preference studies suggest a hierarchy of cyclist and non-cyclist preferences may exist, favoring separate paths and/or lanes over cycling on roadways with traffic - particularly with high volumes of fast-moving motorized traffic. Revealed- and stated-route-choice studies indicate that intersections have negative effects on the cycling experience, but that certain features can offset this. The research correlating link and node characteristics to cycling implies that networks of such facilities would have positive effects, though very few empirical studies link complex measures of the network to cycling levels. In spite of an increase in studies and general agreement among findings, several important research gaps remain, including empirical studies using comprehensive network measures and studies of specific facility designs and new types of facilities (including intersection treatments). Improved research methods are necessary, including better sampling, longitudinal studies, greater geographic diversity, and incorporating more control variables, including policies.
We present new Jansky Very Large Array (VLA) radio images of the Crab nebula at 5.5 GHz, taken at two epochs separated by 6 d about 2 months after a gamma-ray flare in 2012 July. We find no ...significant change in the Crab's radio emission localized to a region of <2 light-months in radius, either over the 6-d interval between our present observations or between the present observations and ones from 2001. Any radio counterpart to the flare has a radio luminosity of less than or equal to 2 x 10 super(-4) times that of the nebula. Comparing our images to one from 2001, we do however find changes in radio brightness, up to 10 per cent in amplitude, which occur on decade time-scales throughout the nebula. The morphology of the changes is complex suggesting both filamentary and knotty structures. The variability is stronger, and the time-scales likely somewhat shorter, nearer the centre of the nebula. We further find that even with the excellent uv-coverage and signal to noise of the VLA, deconvolution errors are much larger than the noise, being up to 1.2 per cent of peak brightness of the nebula in this particular case.
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