scholarly journals Fermi Large Area Telescope observations of the fast-dimming Crab Nebula in 60–600 MeV

2020 ◽  
Vol 638 ◽  
pp. A147 ◽  
Author(s):  
Paul K. H. Yeung ◽  
Dieter Horns
Keyword(s):  
Statistical Significance ◽  
Angular Size ◽  
High Energy ◽  
Transition Time ◽  
Relativistic Electrons ◽  
Synchrotron Emission ◽  
Large Area ◽  
High Energy Part ◽  
Inverse Compton ◽  
Flux State

Context. The Crab pulsar and its nebula are the origin of relativistic electrons which can be observed through their synchrotron and inverse Compton emission. The transition between synchrotron-dominated and inverse-Compton-dominated emissions takes place at ≈109 eV. Aims. The short-term (lasting for one week to months) flux variability of the synchrotron emission from the most energetic electrons is investigated with data from ten years of observations with the Fermi Large Area Telescope in the energy range from 60 MeV to 600 MeV. Methods. We reconstructed the off-pulse light curve reconstructed from phase-resolved data. The corresponding histogram of flux measurements was used to identify distributions of flux-states and the statistical significance of a lower-flux component was estimated with dedicated simulations of mock light curves. The energy spectra for different flux states were also reconstructed. Results. We confirm the presence of flaring-states which follow a log-normal flux distribution. Additionally, we discovered a low-flux state where the flux drops to as low as 18.4% of the intermediate-state average flux and remains there for several weeks. The transition time is observed to be as short as two days. The energy spectrum during the low-flux state resembles the extrapolation of the inverse-Compton spectrum measured at energies beyond several GeV energy, implying that the high-energy part of the synchrotron emission is dramatically depressed. Conclusions. The low-flux state found here and the transition time of at most ten days indicate that the bulk (>75%) of the synchrotron emission above 108 eV originates in a compact volume with apparent angular size of θ ≈ 0″​​.4 tvar/(5 d). We tentatively infer that the so-called inner knot feature is the origin of the bulk of the γ-ray emission.

scholarly journals A Possible Discovery of a Flaring 1012 eV Gamma-Ray Source near the Red Dwarf EV Lac

1995 ◽  
Vol 151 ◽  
pp. 78-79
Author(s):  
I.Yu. Alekseev ◽  
N.N. Chalenko ◽  
V.P. Fomin ◽  
R.E. Gershberg ◽  
O.R. Kalekin ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Electronic Device ◽  
Angular Size ◽  
High Energy ◽  
Optical Systems ◽  
Relativistic Electrons ◽  
Large Area ◽  
Γ Rays ◽  
Γ Ray ◽  
Ev Lac

During the 1994 coordinated observations of the red dwarf flare star EV Lac, the star was monitored in the very high energy (VHE) γ-ray range around 1012 eV with the Crimean ground-based γ-ray telescope GT-48. This telescope consists of two identical optical systems (Vladimirsky et al. 1994) which were directed in parallel on EV Lac.The detection principle of the VHE γ-rays is based on the Čerenkov radiation emitted by relativistic electrons and positrons. The latter are generated in the interaction of the γ-rays with nuclei in the Earth’s atmosphere that leads to an appearance of a shower of charged particles and γ-quanta. The duration of the Cherenkov radiation flash is very short, just about a few nanoseconds. The angular size of the shower is ∼ 1°. To detect such flashes we use an optical system with large area mirrors and a set of 37 photomultipliers (PMs) in the focal plane. Using the information from these PMs which are spaced hexagonally and correspond to a field of view of 2°.6 on the sky, we can obtain the image of an optical flash. The electronic device permits us to detect nanosecond flashes (40 ns exposure time and 12 μs readout dead-time).

scholarly journals Recent Results from the CANGAROO Project

1996 ◽  
Vol 160 ◽  
pp. 363-364
Author(s):  
S.A. Dazeley ◽  
P.G. Edwards ◽  
J.R. Patterson ◽  
G.P. Rowell ◽  
M. Sinnott ◽  
...  
Keyword(s):  
Gamma Rays ◽  
South Australia ◽  
Cosmic Ray ◽  
High Energy ◽  
Relativistic Electrons ◽  
Large Numbers ◽  
Inverse Compton ◽  
Very High Energy ◽  
Large Telescopes ◽  
Very High

TheCollaboration ofAustralia andNippon for aGAmmaRayObservatory in theOutback operates two large telescopes at Woomera (South Australia), which detect the Čerenkov light images produced in the atmosphere by electronpositron cascades initiated by very high energy (~1 TeV or 1012eV) gamma rays. These gamma rays arise from a different mechanism than at EGRET energies: inverse Compton (IC) emission from relativistic electrons.The spoke-like images are recorded by a multi-pixel camera which facilitates the rejection of the large numbers of oblique and ragged cosmic ray images. A field of view ~3.5° is required. The Australian team operates a triple 4 m diameter mirror telescope, BIGRAT, with a 37 photomultiplier tube camera and energy threshold 600 GeV. The Japanese operate a single, highly accurate 3.8 m diameter f/1 telescope and high resolution 256 photomultipler tube camera. In 1998 a new 7 m telescope is planned for Woomera with a design threshold ~;200GeV.

scholarly journals Very High Energy γ-Ray Generation Near The Light Cylinder of an Axisymmetric Rotator: Cos-B Like γ-Ray Sources

1992 ◽  
Vol 128 ◽  
pp. 207-208
Author(s):  
S. V. Bogovalov ◽  
YU. D. Kotov
Keyword(s):  
High Energy ◽  
Relativistic Electrons ◽  
X Rays ◽  
Inverse Compton Scattering ◽  
Light Cylinder ◽  
Radiation Spectra ◽  
Inverse Compton ◽  
Very High Energy ◽  
Γ Ray ◽  
Very High

AbstractSuper-hard γ-ray radiation spectra have been calculated. This radiation is generated near the velocity-of-light cylinder through the process of inverse-Compton scattering of relativistic electrons by thermal photons radiated by a neutron star. These calculations have been compared with observations of the Crab and Vela pulsars at 1000-GeV γ-ray energies. A correlation between γ-ray flares and those in soft (Ex ≃ lkeV) X-rays are predicted.

scholarly journals Particle Acceleration in Extragalactic Jets and Implications for the High-Energy Emission from Blazars

1994 ◽  
Vol 159 ◽  
pp. 29-32
Author(s):  
R. Schlickeiser ◽  
C. D. Dermer
Keyword(s):  
Compton Scattering ◽  
Accretion Disk ◽  
High Energy ◽  
Relativistic Electrons ◽  
Spectral Evolution ◽  
Inverse Compton Scattering ◽  
Central Engine ◽  
Inverse Compton ◽  
Γ Rays ◽  
Γ Ray

We demonstrate that the prevalence of superluminal sources in the sample of γ-ray blazars and the peak of their luminosity spectra at γ-ray energies can be readily explained if the γ-rays result from the inverse Compton scattering of the accretion disk radiation by relativistic electrons in outflowing plasam jets. Compton scattering of external radiation by nonthermal particles in blazar jets is dominated by accretion disk photons rather than scattered radiation to distances of ∼ 0.01–0.1 pc from the central engine for standard parameters. The size of the γ-ray photosphere and the spectral evolution of the relativistic electron spectra constrain the location of the acceleration and emission sites in these objects.

scholarly journals High Energy Radiation Generated at Boundary Shear Layers of Relativistic Jets

2002 ◽  
Vol 19 (1) ◽  
pp. 22-25 ◽  
Author(s):  
Ł. Stawarz ◽  
M. Ostrowski
Keyword(s):  
Electron Distribution ◽  
Low Frequency ◽  
Cosmic Ray ◽  
High Energy ◽  
Particle Energy ◽  
Relativistic Electrons ◽  
Microwave Background ◽  
Boundary Shear ◽  
Inverse Compton ◽  
Energy Gains

AbstractA simple model of cosmic ray electron acceleration at the jet boundary yields a power law particle energy distribution of ultra-relativistic electrons with an energy cut-off growing with time, and, finally, a growing particle bump at the energy where energy gains equal radiation losses. For such electron distribution, in tens-of-kpc scale jets, we derived the observed time-varying spectra of synchrotron and inverse Compton radiation, including Comptonisation of synchrotron and cosmic microwave background photons. Slowly varying spectral index along the jet in the ‘low frequency’ spectral range is a natural consequence of boundary layer acceleration. Variations of the high energy bump of the electron distribution can give rise to anomalous behaviour in the X-ray band in comparison to the lower frequencies.

scholarly journals Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A

Science ◽  
2013 ◽  
Vol 343 (6166) ◽  
pp. 42-47 ◽  
Author(s):  
M. Ackermann ◽  
M. Ajello ◽  
K. Asano ◽  
W. B. Atwood ◽  
M. Axelsson ◽  
...  
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Synchrotron Emission ◽  
Large Area ◽  
Energy Photon ◽  
Isotropic Energy ◽  
Spectral Analyses ◽  
Gamma Ray Burst ◽  
Γ Ray ◽  
High Energy Emission

The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest γ-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

Predictions of inverse Compton radiation from PSR B1259–63

2000 ◽  
Vol 177 ◽  
pp. 531-532
Author(s):  
J. G. Kirk ◽  
Lewis Ball ◽  
O. Skjæraasen
Keyword(s):  
Synchrotron Radiation ◽  
Delta Function ◽  
Companion Paper ◽  
High Energy ◽  
Termination Shock ◽  
Relativistic Electrons ◽  
X Rays ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Function Approximations

Unpulsed high energy (TeV) emission has been detected from several isolated pulsars (Aharonian 1999) and presumably results from relativistic electrons accelerated at the termination shock of an MHD wind driven by the pulsar itself. These electrons inverse Compton scatter target photons from either the cosmic microwave background, or from their own synchrotron radiation.The rotation-powered binary pulsar PSR B1259–63 (Johnston et al. 1996) is also thought to drive an MHD wind, and the synchrotron radiation of electrons accelerated at its termination shock is probably the source of the unpulsed X-rays seen from this object by ROSAT, OSSE and ASCA (Tavani & Arons 1997). Compared to the isolated pulsars, however, the the pulsar’s Be-star companion provides an energy density of target photons available for inverse Compton scattering which is some 11 orders of magnitude larger. Using delta-function approximations to the emissivities and a monochromatic approximation to the spectrum of the target photons, we modelled the observed X-ray synchrotron emission and predicted the TeV emission in a recent paper (Kirk et al. 1999). In this contribution we improve these calculations in two respects – by treating the target spectrum more precisely, as described in the companion paper (Ball & Kirk 1999), and by relaxing the approximations made in the emissivities.

scholarly journals Results of two balloon flights for the detection of high energy γ-rays

1970 ◽  
Vol 37 ◽  
pp. 325-334 ◽  
Author(s):  
M. Niel ◽  
G. Vedrenne ◽  
R. Bouigue
Keyword(s):  
Galactic Center ◽  
Galactic Disk ◽  
High Energy ◽  
Relativistic Electrons ◽  
Interstellar Matter ◽  
Radiation Background ◽  
Inverse Compton Effect ◽  
Inverse Compton ◽  
Γ Rays ◽  
Energy Processes

After many years of fruitless research on primary γ-Rays, the results obtained by Clark et al. [1] with the OSO-3 satellite, proved for the first time the existence of a primary γ-Ray flux. The study of the distribution of this radiation showed a strong anisotropy in the direction of the galactic disk and, more precisely, in the direction of the galactic center. Now the production of γ-Rays in the spatial medium is related to high energy processes and to the presence of relativistic electrons. The high energy processes bring about an emission of γ-Rays essentially by decay of the π° mesons created for instance, by the interaction of cosmic radiation with interstellar matter or by matter-antimatter annihilation. The relativistic electrons can lead to an emission of γ-Rays by various processes: in particular, by bremsstrahlung of the electrons in the interstellar matter or by the Inverse Compton effect with the photons of the stellar light or of the infrared radiation background.

scholarly journals Suzaku observation of Jupiter’s X-rays around solar maximum

2019 ◽  
Vol 71 (5) ◽  
Author(s):  
Masaki Numazawa ◽  
Yuichiro Ezoe ◽  
Kumi Ishikawa ◽  
Takaya Ohashi ◽  
Yoshizumi Miyoshi ◽  
...  
Keyword(s):  
Solar Activity ◽  
Compton Scattering ◽  
High Energy ◽  
Spectral Studies ◽  
Relativistic Electrons ◽  
X Rays ◽  
Diffuse Emission ◽  
X Ray ◽  
Inverse Compton Scattering ◽  
Inverse Compton

Abstract We report on results of imaging and spectral studies of X-ray emission from Jupiter observed by Suzaku. In 2006, Suzaku found diffuse X-ray emission in 1–5 keV associated with Jovian inner radiation belts. It has been suggested that the emission is caused by the inverse-Compton scattering by ultra-relativistic electrons (∼50 MeV) in Jupiter’s magnetosphere. To confirm the existence of this emission and to understand its relation to the solar activity, we conducted an additional Suzaku observation in 2014 around the maximum of the 24th solar cycle. As a result, we successfully found the diffuse emission around Jupiter in 1–5 keV again, and also found point-like emission in 0.4–1 keV. The luminosity of the point-like emission, which was probably composed of solar X-ray scattering, charge exchange, or auroral bremsstrahlung emission, increased by a factor of ∼5 with respect to the findings from 2006, most likely due to an increase of the solar activity. The diffuse emission spectrum in the 1–5 keV band was well-fitted with a flat power-law function (Γ = 1.4 ± 0.1) as in the past observation, which supported the inverse-Compton scattering hypothesis. However, its spatial distribution changed from ∼12 × 4 Jovian radius (Rj) to ∼20 × 7 Rj. The luminosity of the diffuse emission increased by the smaller factor of ∼3. This indicates that the diffuse emission is not simply responding to the solar activity, which is also known to cause little effect on the distribution of high-energy electrons around Jupiter. Further sensitive study of the spatial and spectral distributions of the diffuse hard X-ray emission is important to understand how high-energy particles are accelerated in Jupiter’s magnetosphere.

KLEIN–NISHINA EFFECTS IN THE PROMPT AND EXTENDED HIGH-ENERGY GAMMA-RAY EMISSION OF GAMMA-RAY BURSTS

2011 ◽  
Vol 20 (10) ◽  
pp. 2023-2027 ◽  
Author(s):  
XIANG-YU WANG ◽  
HAO-NING HE ◽  
ZHUO LI
Keyword(s):  
Gamma Ray ◽  
Early Time ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
Low Energy ◽  
Large Area ◽  
Wide Range ◽  
Inverse Compton ◽  
Energy Gamma ◽  
Gamma Ray Emission

Prompt and extended high-energy (> 100 MeV) gamma-ray emission has been observed from more than ten gamma-ray bursts by Fermi Large Area Telescope (LAT). Such emission is likely to be produced by synchrotron radiation of electrons accelerated in internal or external shocks. We show that IC scattering of these electrons with synchrotron photons are typically in the Klein–Nishina (KN) regime. For the prompt emission, the KN effect can suppress the IC component and as a result, one single component is seen in some strong bursts. The KN inverse-Compton cooling may also affect the low-energy electron number distribution and hence result in a hard low-energy synchrotron photon spectrum. During the afterglow, KN effect makes the Compton-Y parameter generally less than 1 in the first seconds for a wide range of parameter space. Furthermore, we suggest that the KN effect can explain the somewhat faster-than-expected decay of the early-time high-energy emission observed in GRB090510 and GRB090902B.

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