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

2018 ◽  
Vol 615 ◽  
pp. A82 ◽  
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.

scholarly journals Galactic diffuse gamma-ray emission at TeV energy

2020 ◽  
Vol 633 ◽  
pp. A94 ◽  
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.

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

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.

scholarly journals The first catalog of Fermi-LAT sources below 100 MeV

2018 ◽  
Vol 618 ◽  
pp. A22 ◽  
Author(s):  
G. Principe ◽  
D. Malyshev ◽  
J. Ballet ◽  
S. Funk
Keyword(s):  
Energy Range ◽  
Gamma Ray ◽  
Point Sources ◽  
Source Analysis ◽  
Emission Model ◽  
Diffuse Emission ◽  
Large Area ◽  
Spectrum Radio ◽  
Source Confusion ◽  
Bl Lacs

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.

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

2007 ◽  
Author(s):  
Igor V. Moskalenko ◽  
Andrew W. Strong ◽  
Seth W. Digel ◽  
Troy A. Porter ◽  
Keyword(s):  
Emission Model ◽  
Diffuse Emission ◽  
Large Area

scholarly journals Interpreting correlated observations of cosmic rays and gamma-rays from Centaurus A with a proton blazar inspired model

2020 ◽  
Vol 500 (1) ◽  
pp. 1087-1094
Author(s):  
Prabir Banik ◽  
Arunava Bhadra ◽  
Abhijit Bhattacharyya
Keyword(s):  
Cosmic Rays ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Energy Scale ◽  
Electromagnetic Spectrum ◽  
Ultrahigh Energy ◽  
Large Area ◽  
Centaurus A

ABSTRACT The nearest active radio galaxy Centaurus (Cen) A is a gamma-ray emitter in GeV–TeV energy scale. The high energy stereoscopic system (HESS) and non-simultaneous Fermi–Large Area Telescope observation indicate an unusual spectral hardening above few GeV energies in the gamma-ray spectrum of Cen A. Very recently the HESS observatory resolved the kilo parsec (kpc)-scale jets in Centaurus A at TeV energies. On the other hand, the Pierre Auger Observatory (PAO) detects a few ultrahigh energy cosmic ray (UHECR) events from Cen-A. The proton blazar inspired model, which considers acceleration of both electrons and hadronic cosmic rays in active galactic nuclei (AGN) jet, can explain the observed coincident high-energy neutrinos and gamma-rays from Ice-cube detected AGN jets. Here, we have employed the proton blazar inspired model to explain the observed GeV–TeV gamma-ray spectrum features including the spectrum hardening at GeV energies along with the PAO observation on cosmic rays from Cen-A. Our findings suggest that the model can explain consistently the observed electromagnetic spectrum in combination with the appropriate number of UHECRs from Cen A.

scholarly journals The cosmic-ray content of the Orion-Eridanus superbubble

2020 ◽  
Vol 635 ◽  
pp. A96 ◽  
Author(s):  
T. Joubaud ◽  
I. A. Grenier ◽  
J. M. Casandjian ◽  
T. Tolksdorf ◽  
R. Schlickeiser
Keyword(s):  
Cosmic Rays ◽  
Galactic Plane ◽  
Cosmic Ray ◽  
Significant Loss ◽  
Particle Energy ◽  
Stellar Winds ◽  
The Sun ◽  
Large Area ◽  
Average Spectrum ◽  
Cosmic Ray Flux

Aims. The nearby Orion-Eridanus superbubble, which was blown by multiple supernovae several million years ago, has likely produced cosmic rays. Its turbulent medium is still energised by massive stellar winds and it can impact cosmic-ray transport locally. The γ radiation produced in interactions between cosmic rays and interstellar gas can be used to compare the cosmic-ray spectrum in the superbubble and in other regions near the Sun. It can reveal spectral changes induced in GeV to TeV cosmic rays by the past and present stellar activity in the superbubble. Methods. We used ten years of data from the Fermi Large Area Telescope (LAT) in the 0.25–63 GeV energy range to study the closer (Eridanus) end of the superbubble at low Galactic latitudes. We modelled the spatial and spectral distributions of the γ rays produced in the different gas phases (atomic, molecular, dark, and ionised) of the clouds found in this direction. The model included other non-gaseous components to match the data. Results. We found that the γ-ray emissivity spectrum of the gas along the outer rim and in a shell inside the superbubble is consistent with the average spectrum measured in the solar neighbourhood. It is also consistent with the cosmic-ray spectrum directly measured in the Solar System. This homogeneity calls for a detailed assessment of the recent supernova rate and current census of massive stellar winds in the superbubble in order to estimate the epoch and rate of cosmic-ray production and to constrain the transport conditions that can lead to such homogeneity and little re-acceleration. We also found significant evidence that a diffuse atomic cloud lying outside the superbubble, at a height of 200–250 pc below the Galactic plane, is pervaded by a 34% lower cosmic-ray flux, but with the same particle energy distribution as the local one. Super-GeV cosmic rays should freely cross such a light and diffuse cirrus cloud without significant loss or spectral distorsion. We tentatively propose that the cosmic-ray loss relates to the orientation of the magnetic field lines threading the cirrus, which point towards the halo according to the dust polarisation data from Planck. Finally, we gathered the present emissivity measurements with previous estimates obtained around the Sun to show how the local cosmic-ray flux decreases with Galactic height and to compare this trend with model predictions.

scholarly journals Fermi Large Area Telescope observation of high-energy solar flares: constraining emission scenarios

2015 ◽  
Vol 11 (S320) ◽  
pp. 51-56
Author(s):  
Nicola Omodei ◽  
Melissa Pesce-Rollins ◽  
Vahè Petrosian ◽  
Wei Liu ◽  
Fatima Rubio da Costa ◽  
...  
Keyword(s):  
Solar Flares ◽  
Gamma Ray ◽  
Solar Energetic Particle ◽  
Cosmic Ray ◽  
Impulsive Phase ◽  
High Energy ◽  
Solar Energetic Particle Event ◽  
Emission Scenarios ◽  
Large Area ◽  
Gamma Ray Emission

AbstractThe Fermi Large Area Telescope (LAT) is the most sensitive instrument ever deployed in space for observing gamma-ray emission >100 MeV. This has also been demonstrated by its detection of quiescent gamma-ray emission from pions produced by cosmic-ray protons interacting in the solar atmosphere, and from cosmic-ray electron interactions with solar optical photons. The Fermi-LAT has also detected high-energy gamma-ray emission associated with GOES M-class and X-class solar flares, each accompanied by a coronal mass ejection and a solar energetic particle event, increasing the number of detected solar flares by almost a factor of 10 with respect to previous space observations. During the impulsive phase, gamma rays with energies up to several hundreds of MeV have been recorded by the LAT. Emission up to GeV energies lasting several hours after the flare has also been detected by the LAT. Of particular interest are the recent detections of three solar flares whose position behind the limb was confirmed by the STEREO satellites. While gamma-ray emission up to tens of MeV resulting from proton interactions has been detected before from occulted solar flares, the significance of these particular events lies in the fact that these are the first detections of >100 MeV gamma-ray emission from footpoint-occulted flares. We will present the Fermi-LAT, RHESSI and STEREO observations of these flares and discuss the various emission scenarios for these sources.

scholarly journals Indirect searches for dark matter with the Fermi LAT instrument

2014 ◽  
Vol 29 (22) ◽  
pp. 1430030 ◽  
Author(s):  
M. N. Mazziotta ◽  
Keyword(s):  
Dark Matter ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
Weakly Interacting Massive Particles ◽  
Current Status ◽  
Large Area ◽  
Weakly Interacting ◽  
Electron Positron ◽  
Massive Particles ◽  
Particle Dark Matter

In this review the current status of several searches for particle dark matter with the Fermi Large Area Telescope instrument is presented. In particular, the current limits on the weakly interacting massive particles, obtained from the analyses of gamma-ray and cosmic ray electron/positron data, will be illustrated.

scholarly journals Hard and bright gamma-ray emission at the base of the Fermi bubbles

2019 ◽  
Vol 625 ◽  
pp. A110 ◽  
Author(s):  
L. Herold ◽  
D. Malyshev
Keyword(s):  
Power Law ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Galactic Center ◽  
Galactic Plane ◽  
Point Sources ◽  
High Latitudes ◽  
Large Area ◽  
Inverse Compton Scattering ◽  
Gamma Ray Emission

Context. The Fermi bubbles (FBs) are large gamma-ray emitting lobes extending up to 55° in latitude above and below the Galactic center (GC). Although the FBs were discovered eight years ago, their origin and the nature of the gamma-ray emission are still unresolved. Understanding the properties of the FBs near the Galactic plane may provide a clue to their origin. Previous analyses of the gamma-ray emission at the base of the FBs, what remains after subtraction of Galactic foregrounds, have shown an increased intensity compared to the FBs at high latitudes, a hard power-law spectrum without evidence of a cutoff up to approximately 1 TeV, and a displacement of the emission to negative longitudes relative to the GC. Aims. We analyze nine years of Fermi Large Area Telescope data in order to study in more detail than the previous analyses the gamma-ray emission at the base of the FBs, especially at energies above 10 GeV. Methods. We used a template analysis method to model the observed gamma-ray data and calculate the residual emission after subtraction of the expected foreground and background emission components. Since there are large uncertainties in the determination of the Galactic gamma-ray emission toward the GC, we used several methods to derive Galactic gamma-ray diffuse emission and the contribution from point sources to estimate the uncertainties in the emission at the base of the FBs. Results. We confirm that the gamma-ray emission at the base of the FBs is well described by a simple power law up to 1 TeV energies. The 95% confidence lower limit on the cutoff energy is about 500 GeV. It has larger intensity than the FBs emission at high latitudes and is shifted to the west (negative longitudes) from the GC. If the emission at the base of the FBs is indeed connected to the high-latitude FBs, then the shift of the emission to negative longitudes disfavors models in which the FBs are created by the supermassive black hole at the GC. We find that the gamma-ray spectrum can be explained either by gamma rays produced in hadronic interactions or by leptonic inverse Compton scattering. In the hadronic scenario, the emission at the base of the FBs can be explained either by several hundred supernova remnants (SNRs) near the GC or by about ten SNRs at a distance of ~1 kpc. In the leptonic scenario, the necessary number of SNRs that can produce the required density of CR electrons is a factor of a few larger than in the hadronic scenario.

Upper limit to the number of galactic sources of ultra-high-energy gamma-rays

1989 ◽  
Vol 8 (2) ◽  
pp. 159-160 ◽  
Author(s):  
D. J. Bird ◽  
R. W. Clay ◽  
P. G. Edwards
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Galactic Plane ◽  
Cosmic Ray ◽  
High Energy ◽  
Ultra High Energy ◽  
Upper Limits ◽  
Energy Gamma ◽  
Galactic Sources ◽  
Cosmic Ray Flux

AbstractThe extreme isotropy of cosmic ray events allows one to put upper limits on any possible non-isotropic contribution to the flux. In particular, one can investigate any excess of events which may be confined to the galactic plane. Such extra events would be expected from galactic ultra-high-energy (UHE) gamma-ray sources. Under the assumption of an isotropic cosmic ray flux, recent Buckland Park data place a 95% confidence level limit on the total southern hemisphere (declination −15° to −55°) flux of UHE gamma-rays at between 0.6 and 6 equivalent Cygnus X-3 sources, depending on assumptions concerning the gamma-ray spectrum.

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