Galactic gamma rays from the inverse Compton process

Giller, M.; Wdowczyk, J.; Wolfendale, A. W.; Zhang, L.

doi:10.1088/0954-3899/21/3/021

Cited by 9 publications

(8 citation statements)

References 10 publications

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“…Chi et al calculated intensities of ~ 8 × 10 -6 photons cm -2 s -1 ster -1 and an index of ~ -1.95; they used the same photon field as Bloemen (Mathis et al 1983), but estimated the cosmic-ray electron scale height to be on the order of 5 kpc rather than 750 pc. Giller et al (1995) Using the longitude dependence correlations, we derived a spectral index of -2.2 ± 0.2, consistent with the model predictions, and lower limits of (9.7 ± 2.7) × 10 -6 photons cm -2 s -1 ster -1 in the 30-100 MeV band and (3.3 ± 0.7) × 10 -6 photons cm -2 s -1 ster -1 for E > 100 MeV toward the galactic center. Using a model containing an isotropic component, an IC component proportional to the 408 MHz synchrotron radiation, and a spatially varying emissivity with respect to H I, we found a spectral index of -1.88 ± 0.14 and average intensities of (7.9 ± 2.9) × 10 -6 photons cm -2 s -1 ster -1 in the 30-100 MeV band and (5.0 ± 0.8) × 10 -6 photons cm -2 s -1 ster -1 for E > 100 MeV.…”

Section: Discussionmentioning

confidence: 99%

The Inverse Compton and Extragalactic Components of Diffuse Gamma-Ray Emission

Chen

Dwyer²,

Kaaret

1996

ApJ

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We present spectra of the inverse-Compton and extragalactic components of the high-energy gamma-radiation based on an analysis of eight high-latitude (29°.5 < |b| < 74°) regions. The spectrum of gamma-radiation that is correlated with atomic hydrogen (H I) column density indicates that this component originates in cosmic-ray/matter interactions. The gamma-ray emission uncorrelated with H I varies as a function of galactic longitude and is correlated with radio continuum emission (408 MHz), which is dominated by synchrotron radiation from cosmic-ray electrons. We interpret the longitude-dependent variation in the intensity of gamma-ray emission uncorrelated with H I as a model-independent, direct measure of the spatially varying part of the inverse-Compton (IC) emission from the galactic halo. We find an intensity change (center versus anticenter) of (3.3 ± 0.7) × 10 -6 photons cm -2 s -1 ster -1 for E > 100 MeV, a statistically significant (> 4σ) result. This value is a lower limit to the intensity of inverse-Compton gamma-ray emission towards the galactic center at high latitudes.We correlate the gamma-ray intensity with a model consisting of an isotropic component, a component proportional to the 408 MHz synchrotron radiation, and an HI component with different emissivities in eight galactic octants. Using this fit, we measure the spectrum and absolute intensity of the IC emission. We obtain a spectral index of -1.85 ± 0.17, in agreement with measurements of the near-earth electron cosmic-ray spectrum, and an average intensity of (5.0 ± 0.8) × 10 -6 photons cm -2 s -1 ster -1 for E > 100 MeV. Extrapolating the IC emission to zero galactic radio continuum intensity, we find that the extragalactic gamma-radiation has a spectral index of -2.15 ± 0.06 and an intensity of (1.24 ± 0.06) × 10 -5 photons cm -2 s -1 ster -1 for E > 100 MeV. The spectrum is consistent with those measured for gamma-ray loud AGN and lends support to interpretation of the extragalactic radiation as due to unresolved gamma-ray emitting AGN.

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Section: Discussionmentioning

confidence: 99%

The Inverse Compton and Extragalactic Components of Diffuse Gamma-Ray Emission

Chen

Dwyer²,

Kaaret

1996

ApJ

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“…In a recent paper (Giller et al 1995) examined CGRO data in some detail and concluded that for latitudes near |b| = 90 • , IC interactions are responsible for 44% of the total galactic intensity. This figure is bigger than had been estimated by others but we consider it to be valid.…”

Section: The Inverse Compton Contributionmentioning

confidence: 99%

Cosmic gamma rays from the Large Magellanic Cloud - and from the Galaxy

Al-Dargazelli

Wolfendale

Zhang

1996

J. Phys. G: Nucl. Part. Phys.

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An analysis has been made of gamma rays from the Large Magellanic Cloud (LMC) using data from the Compton Gamma Ray Observatory. After correcting for foreground gamma rays from cosmic ray (CR) interactions in our own Galaxy it is found that the gamma ray intensity maps show a displacement of peak position away from the peak of the atomic gas contours and towards the peak of the starlight contours. An explanation is advanced in terms of there being an increasing contribution from inverse Compton interactions, this contribution being bigger the higher the energy.Our earlier contention that the average cosmic ray intensity within the LMC is only about 15% of that in the Galaxy is confirmed.

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“…In particular, detailed predictions of IC gamma-rays above 70 − 100 MeV have been made by Bloemen [15] and Chi et al [16], with estimates of the contribution by this component being up to ∼ 50% of the diffuse intensity at medium galactic latitudes (|b| = 10 • to 20 • ). An analysis of EGRET data by Giller et al [17] has suggested a contribution by IC of ∼ 30% for medium latitudes, and up to ∼ 45% toward the galactic pole, in the energy range 30 − 4000 MeV. Strong et al [12] have shown that an IC component is required to provide a good fit to the gamma-ray data from 1 MeV to 1 GeV; see also Bertsch et al [10] and Hunter et al [14].…”

Section: Introductionmentioning

confidence: 99%

Cosmic-ray electrons and the diffuse gamma-ray spectrum

Porter

Protheroe

1997

J. Phys. G: Nucl. Part. Phys.

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Short Title: Cosmic-ray electrons and diffuse gamma-ray spectrum PACS Numbers: 98.70.Sa Cosmic-rays (including sources, origin, acceleration, and interactions) 95.85.Pw Gamma-ray 98.70.Vc Background radiations AbstractThe bulk of the diffuse galactic gamma-ray emission above a few tens of GeV has been conventionally ascribed to the decay of neutral pions produced in cosmic-ray interactions with interstellar matter. Cosmic-ray electrons may, however, make a significant contribution to the gamma-ray spectrum at high energies, and even dominate at TeV-PeV energies depending on their injection spectral index and acceleration cut-off energy. If the injection spectrum is flat, the highest energy electrons will also contribute a diffuse hard X-ray/soft gamma-ray flux via synchrotron emission, and this may offer an explanation for the OSSE observation of a steep spectrum below a few MeV from the inner Galaxy. We perform a propagation calculation for cosmic-ray electrons, and use the resulting interstellar electron spectrum to obtain the gamma-ray spectrum due to inverse Compton, synchrotron and bremsstrahlung interactions consistently from MeV to PeV energies. We compare our results with available observations from satellite-borne telescopes, opticaľ Cerenkov telescopes and air shower arrays and place constraints on the injection spectrum of cosmic-ray electrons. With future observations at TeV-PeV energies it should be possible to determine the average interstellar spectrum of cosmic-ray electrons, and hence estimate their spectrum on acceleration.

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Galactic gamma rays from the inverse Compton process

Cited by 9 publications

References 10 publications

The Inverse Compton and Extragalactic Components of Diffuse Gamma-Ray Emission

The Inverse Compton and Extragalactic Components of Diffuse Gamma-Ray Emission

Cosmic gamma rays from the Large Magellanic Cloud - and from the Galaxy

Cosmic-ray electrons and the diffuse gamma-ray spectrum

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