Developing the Galactic diffuse emission model for the GLAST Large Area Telescope

We present the first Fermi Large Area Telescope (LAT) low energy catalog (1FLE) of sources detected in the energy range 30 – 100 MeV. The imaging Compton telescope (COMPTEL) onboard NASA’s Compton Gamma-Ray Observatory detected sources below 30 MeV, while catalogs of point sources released by the Fermi-LAT and EGRET collaborations use energies above 100 MeV. Because the Fermi-LAT detects gamma rays with energies as low as 20 MeV, we create a list of sources detected in the energy range between 30 and 100 MeV, which closes a gap of point source analysis between the COMPTEL catalog and the Fermi-LAT catalogs. One of the main challenges in the analysis of point sources is the construction of the background diffuse emission model. In our analysis, we use a background-independent method to search for point-like sources based on a wavelet transform implemented in the PGWave code. The 1FLE contains 198 sources detected above 3σ significance with eight years and nine months of the Fermi-LAT data. For 187 sources in the 1FLE catalog we have found an association in the Fermi-LAT 3FGL catalog: 148 are extragalactic, 22 are Galactic, and 17 are unclassified in the 3FGL. The ratio of the number of flat spectrum radio quasars (FSRQ) to BL Lacertae (BL Lacs) in 1FLE is three to one, which can be compared with an approximately 1:1 ratio for the 3FGL or a 1:6 ratio for 3FHL. The higher ratio of the FSRQs in the 1FLE is expected due to generally softer spectra of FSRQs relative to BL Lacs. Most BL Lacs in 1FLE are of low-synchrotron peaked blazar type (18 out of 31), which have softer spectra and higher redshifts than BL Lacs on average. Correspondingly, we find that the average redshift of the BL Lacs in 1FLE is higher than in 3FGL or 3FHL. There are 11 sources that do not have associations in the 3FGL. Most of the unassociated sources either come from regions of bright diffuse emission or have several known 3FGL sources in the vicinity, which can lead to source confusion. The remaining unassociated sources have significance less than 4σ.

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Developing the Galactic Diffuse Emission Model for the GLAST Large Area Telescope

10.2172/903007 ◽

2007 ◽

Author(s):

Igor V. Moskalenko ◽

Andrew W. Strong ◽

Seth W. Digel ◽

Troy A. Porter

Keyword(s):

Emission Model ◽

Diffuse Emission ◽

Large Area

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A new gamma-ray source unveiled by AGILE in the region of Orion

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732333 ◽

2018 ◽

Vol 615 ◽

pp. A82 ◽

Cited By ~ 3

Author(s):

N. Marchili ◽

G. Piano ◽

M. Cardillo ◽

A. Giuliani ◽

S. Molinari ◽

...

Keyword(s):

Stellar Wind ◽

Gamma Ray ◽

Galactic Plane ◽

Direct Detection ◽

Cosmic Ray ◽

Emission Model ◽

Small Contribution ◽

Diffuse Emission ◽

Large Area ◽

Agile Satellite

Context. Diffuse galactic γ-ray emission is produced by the interaction of cosmic rays (CRs) with the interstellar environment. The study of γ-ray emission is therefore a powerful tool that can be used to investigate the origin of CRs and the processes through which they are accelerated. Aims. Our aim is to gain deeper insights into the nature of γ-ray emission in the region of Orion, which is one of the best studied sites of ongoing star formation, by analysing data from the AGILE satellite. Because of the large amount of interstellar medium (ISM) present in it, the diffuse γ-ray emission expected from the Orion region is relatively high. Its separation from the galactic plane also ensures a very small contribution from foreground or background emission, which makes it an ideal site for studying the processes of particle acceleration in star-forming environments. Methods. The AGILE data are modelled through a template that quantifies the γ-ray diffuse emission expected from atomic and molecular hydrogen. Other sources of emission, such as inverse Compton (IC) scattering in interstellar radiation fields (ISRF) and extragalactic background, can be modelled as an isotropic contribution. Results. Gamma-ray emission exceeding the amount expected by the diffuse emission model is detected with a high level of significance. The main excess is in the high-longitude part of Orion A, which confirms previous results from the Fermi Large Area Telescope. A thorough analysis of this feature suggests a connection between the observed γ-ray emission and the B0.5 Ia star κ Orionis. Conclusions. We present the results of the investigation of γ-ray diffuse galactic emission from the region of Orion. The comparison between modelled and observed emission points towards the existence of higher-than-expected γ-ray flux from a 1° radius region centred in κ Orionis, compatible with the site where stellar wind collides with the ISM. Scattering on dark gas and cosmic-ray acceleration at the shock between the two environments are both discussed as possible explanations, with the latter hypothesis being supported by the hardness of the energy spectrum of the emission. If confirmed, this would be the first direct detection of γ-ray emission from the interaction between ISM and a single star’s stellar wind.

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Diffuse Gamma Rays of Galactic and Extragalactic Origin: Preliminary Results from EGRET

Symposium - International Astronomical Union ◽

10.1017/s0074180900110162 ◽

1996 ◽

Vol 168 ◽

pp. 279-288

Author(s):

P. Sreekumar ◽

D.A. Kniffen

Keyword(s):

Gamma Rays ◽

Gamma Ray ◽

Cosmic Ray ◽

High Energy ◽

Emission Model ◽

Diffuse Emission ◽

Interstellar Gas ◽

Cosmic Ray Interactions ◽

Galactic Model ◽

Energy Gamma

The all-sky survey in high energy gamma rays (E>30 MeV) carried out by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory provides for the first time an opportunity to examine in detail diffuse gamma-ray emission of extra-galactic origin. The observed diffuse emission at high galactic latitudes is generally assumed to have a galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation, in addition to an isotropic component presumably of extragalactic origin. The galactic component can be estimated from a model of the interstellar medium and cosmic-ray distribution. Since the derived extragalactic spectrum depends very much on the success of our galactic model, the consistency of the galactic diffuse emission model is examined both spectrally and spatially with existing EGRET observations. In conjunction with this model, EGRET observations of the high latitude emission are used to examine the flux and spectrum of the residual extragalactic emission. This residual emission could be either truly diffuse in origin or could arise from accumulated emission from unresolved sources particularly in the light of EGRET observations showing the presence of numerous gamma-ray bright active galactic nuclei.

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STATUS AND PERSPECTIVES OF GLAST GAMMA RAY EXPERIMENT

International Journal of Modern Physics A ◽

10.1142/s0217751x05030703 ◽

2005 ◽

Vol 20 (29) ◽

pp. 7009-7011

Author(s):

◽

N. GIGLIETTO

Keyword(s):

Active Galactic Nuclei ◽

Supernova Remnants ◽

Gamma Ray ◽

Galactic Nuclei ◽

High Energy ◽

Field Of View ◽

Current Status ◽

Large Field ◽

Diffuse Emission ◽

Large Area

GLAST, the Gamma-ray Large Area Telescope, is a satellite-based experiment able to measure the cosmic gamma-ray flux in the energy range between 20 MeV and 300 GeV or above. The sensitivity is more than 30 times respect to EGRET and the good spatial and time resolution over a large field of view let us to cover a large variety of high energy phenomena. In particular GLAST will be able to study both diffuse emission and point-like gamma ray sources, including active galactic nuclei, gamma ray bursts, pulsars and supernova remnants. In addition, the potentialities of GLAST to explore rare or exotic phenomena like supersymmetric dark matter annihilations will be shown. The present knowledge of the science opportunities that the GLAST experiment can explore will be completed with the detector description and the current status of the experiment.

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Galactic diffuse gamma-ray emission at TeV energy

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936368 ◽

2020 ◽

Vol 633 ◽

pp. A94 ◽

Cited By ~ 3

Author(s):

A. Neronov ◽

D. Semikoz

Keyword(s):

Emission Spectrum ◽

Gamma Ray ◽

Galactic Plane ◽

Cosmic Ray ◽

Galactic Latitude ◽

Diffuse Emission ◽

Large Area ◽

High Galactic Latitude ◽

Galactic Emission ◽

Significant Difference

Context. Measuring the diffuse Galactic γ-ray flux in the TeV range is difficult for ground-based γ-ray telescopes because of the residual cosmic-ray background, which is higher than the γ-ray flux by several orders of magnitude. Its detection is also challenging for space-based telescopes because of low signal statistics. Aims. We characterise the diffuse TeV flux from the Galaxy using decade-long exposures of the Fermi Large Area Telescope. Methods. Considering that the level of diffuse Galactic emission in the TeV band approaches the level of residual cosmic-ray background, we estimated the level of residual cosmic-ray background in the SOURCEVETO event selection and verified that the TeV diffuse Galactic emission flux is well above the residual cosmic-ray background up to high Galactic latitude regions. Results. We study spectral and imaging properties of the diffuse TeV signal from the Galactic plane. We find much stronger emission from the inner Galactic plane than in previous HESS telescope estimates (lower bound). We also find a significant difference in the measurement of the Galactic longitude and latitude profiles of the signal measured by Fermi and HESS. These discrepancies are presumably explained by the fact that regions of background estimate in HESS have non-negligible γ-ray flux. Comparing Fermi measurements with those of ARGO-YBJ, we find better agreement, with the notable exception of the Cygnus region, where we find much higher flux (by a factor 1.5). We also measure the TeV diffuse emission spectrum up to high Galactic latitude and show that the spectra of different regions of the sky have spectral slopes consistent with Γ = 2.34 ± 0.04, which is harder than the slope of the locally observed spectrum of cosmic rays with energies 10–100 TeV, which produce TeV diffuse emission on their way through the interstellar medium. We discuss the possible origin of the hard slope of the TeV diffuse emission. Conclusions. Fermi/LAT provides reliable measurements of the diffuse Galactic emission spectrum in the TeV range, which are almost background free at low Galactic latitudes. The diffuse flux becomes comparable to the residual cosmic-ray background at Galactic latitudes |b| > 50°. Its measurement in these regions might suffer from systematic uncertainty stemming from the uncertainty of our phenomenological model of the residual cosmic-ray background in the Pass 8 Fermi/LAT data.

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Spectral Modeling of Flares in Long-term Gamma-Ray Light Curve of PKS 0903-57

The Astrophysical Journal ◽

10.3847/1538-4357/ac11fa ◽

2021 ◽

Vol 922 (2) ◽

pp. 160

Author(s):

Sandeep Kumar Mondal ◽

Raj Prince ◽

Nayantara Gupta ◽

Avik Kumar Das

Keyword(s):

Gamma Ray ◽

Spectral Energy ◽

Emission Region ◽

Multiple Time ◽

Emission Model ◽

X Rays ◽

Large Area ◽

Bl Lacertae ◽

First Time

Abstract A detailed study of the BL Lacertae PKS 0903-57 has been done for the first time with 12 yr of Fermi Large Area Telescope data. We have identified two bright gamma-ray flares in 2018 and 2020. Many substructures were observed during multiple time binning of these flares. We performed a detailed temporal and spectral study on all the substructures separately. A single-zone emission model is used for time-dependent leptonic modeling of the multiwavelength spectral energy distributions. Our estimated values of variability timescale, magnetic field in the emission region, and the jet power obtained from leptonic modeling of PKS 0903-57 are presented in this work. Currently, we have a minimal number of observations in X-rays and other bands. Hence, further simultaneous multiwavelength monitoring of this source is required to have a better understanding of the physical processes occurring in the jet of the blazar PKS 0903-57.

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Searching for gamma-ray emission from galaxy clusters at low redshift

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3263 ◽

2019 ◽

Vol 491 (3) ◽

pp. 3225-3244 ◽

Cited By ~ 3

Author(s):

Manuel Colavincenzo ◽

Xiuhui Tan ◽

Simone Ammazzalorso ◽

Stefano Camera ◽

Marco Regis ◽

...

Keyword(s):

Cross Correlation ◽

Gamma Ray ◽

Signal To Noise Ratio ◽

Galaxy Cluster ◽

Accurate Estimation ◽

X Rays ◽

Diffuse Emission ◽

Large Area ◽

Significant Case ◽

Gamma Ray Emission

ABSTRACT We report the identification of a positive cross-correlation signal between the unresolved gamma-ray emission, measured by the Fermi Large Area Telescope, and four different galaxy cluster catalogues. The selected catalogues peak at low-redshift and span different frequency bands, including infrared, optical, and X-rays. The signal-to-noise ratio of the detected cross-correlation amounts to 3.5 in the most significant case. We investigate and comment about its possible origin, in terms of compact gamma-ray emission from AGNs inside clusters or diffuse emission from the intracluster medium. The analysis has been performed by introducing an accurate estimation of the cross-correlation power-spectrum covariance matrix, built with mock realizations of the gamma and galaxy cluster maps. Different methods to produce the mock realizations starting from the data maps have been investigated and compared, identifying suitable techniques which can be generalized to other cross-correlation studies.

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Convergent Beam Electron Diffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100070072 ◽

1978 ◽

Vol 36 (3) ◽

pp. 304-315

Author(s):

G. Lehmpfuhl

Keyword(s):

Electron Diffraction ◽

Diffraction Pattern ◽

Crystal Surface ◽

Diffraction Spot ◽

Crystal Thickness ◽

Large Area ◽

Electron Microscopic ◽

Additional Information ◽

Microscopic Investigations

Introduction In electron microscopic investigations of crystalline specimens the direct observation of the electron diffraction pattern gives additional information about the specimen. The quality of this information depends on the quality of the crystals or the crystal area contributing to the diffraction pattern. By selected area diffraction in a conventional electron microscope, specimen areas as small as 1 µ in diameter can be investigated. It is well known that crystal areas of that size which must be thin enough (in the order of 1000 Å) for electron microscopic investigations are normally somewhat distorted by bending, or they are not homogeneous. Furthermore, the crystal surface is not well defined over such a large area. These are facts which cause reduction of information in the diffraction pattern. The intensity of a diffraction spot, for example, depends on the crystal thickness. If the thickness is not uniform over the investigated area, one observes an averaged intensity, so that the intensity distribution in the diffraction pattern cannot be used for an analysis unless additional information is available.

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TEM Study of a Tilt Boundary in Hot-Pressed Silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100097454 ◽

1981 ◽

Vol 39 ◽

pp. 160-161

Author(s):

C. B. Carter ◽

J. Rose ◽

D. G. Ast

Keyword(s):

Electron Diffraction ◽

Imaging Technique ◽

Interface Structure ◽

Large Area ◽

Weak Beam ◽

Lattice Fringe ◽

Electron Diffraction Technique ◽

Tilt Boundaries ◽

Beam Technique ◽

Twist Boundaries

The hot-pressing technique which has been successfully used to manufacture twist boundaries in silicon has now been used to form tilt boundaries in this material. In the present study, weak-beam imaging, lattice-fringe imaging and electron diffraction techniques have been combined to identify different features of the interface structure. The weak-beam technique gives an overall picture of the geometry of the boundary and in particular allows steps in the plane of the boundary which are normal to the dislocation lines to be identified. It also allows pockets of amorphous SiO2 remaining in the interface to be recognized. The lattice-fringe imaging technique allows the boundary plane parallel to the dislocation to be identified. Finally the electron diffraction technique allows the periodic structure of the boundary to be evaluated over a large area - this is particularly valuable when the dislocations are closely spaced - and can also provide information on the structural width of the interface.

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