The interstellar radiation field: a datum for cosmic ray physics

Chi, X.; Wolfendale, A. W.

doi:10.1088/0954-3899/17/6/018

Cited by 25 publications

(24 citation statements)

References 11 publications

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“…Bloemen (1985) extended the MMP83 work to study the IC emission in the context of COS-B data, but noted the model shortcomings toward the inner Galaxy because of the artificial cut-off for R 3 kpc in the stellar spatial distribution. Chi & Wolfendale (1991) augmented the MMP83 stellar model with the dust emission results described by Cox et al (1986) and re-calculated the spatial distribution of the ISRF energy density. This work was used by the EGRET team as input to their modelling of the high-energy interstellar γ-ray emission (Bertsch et al 1993;Hunter et al 1997).…”

Section: Interstellar Radiation Fieldmentioning

confidence: 99%

High-energy Gamma Rays from the Milky Way: Three-dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities in the Interstellar Medium

Porter

Jóhannesson

Moskalenko

2017

ApJ

145

215

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High-energy γ-rays of interstellar origin are produced by the interaction of cosmic-ray (CR) particles with the diffuse gas and radiation fields in the Galaxy. The main features of this emission are well understood and are reproduced by existing CR propagation models employing 2D Galactocentric cylindrically symmetrical geometry. However, the high-quality data from instruments like the Fermi Large Area Telescope reveal significant deviations from the model predictions on few to tens of degree scales indicating the need to include the details of the Galactic spiral structure and thus require 3D spatial modelling. In this paper the high-energy interstellar emissions from the Galaxy are calculated using the new release of the GALPROP code employing 3D spatial models for the CR source and interstellar radiation field (ISRF) densities. Three models for the spatial distribution of CR sources are used that are differentiated by their relative proportion of input luminosity attributed to the smooth disc or spiral arms. Two ISRF models are developed based on stellar and dust spatial density distributions taken from the literature that reproduce local near-to far-infrared observations. The interstellar emission models that include arms and bulges for the CR source and ISRF densities provide plausible physical interpretations for features found in the residual maps from high-energy γ-ray data analysis. The 3D models for CR and ISRF densities provide a more realistic basis that can be used for the interpretation of the non-thermal interstellar emissions from the Galaxy.

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Section: Interstellar Radiation Fieldmentioning

confidence: 99%

High-energy Gamma Rays from the Milky Way: Three-dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities in the Interstellar Medium

Porter

Jóhannesson

Moskalenko

2017

ApJ

145

215

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“…The distributions of both CR electrons and protons through the Galaxy were assumed correlated with the distribution of gas, and modeled by convolving the total gas distribution (H I, H 2 and H II) with a two-dimensional Gaussian filter of HWHM r 0 = 1.76 kpc (Hunter et al 1997 and the references therein). The distributions and the energy densities of the low energy radiation fields, necessary for a calculation of the inverse-Compton component of the Galactic γ-ray emission, were based on the calculations of Chi & Wolfendale (1991).…”

Section: Descriptionmentioning

confidence: 99%

The case for a low extragalactic gamma-ray background

Keshet¹,

Waxman²,

Loeb³

2004

J. Cosmol. Astropart. Phys.

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Measurements of the diffuse extragalactic γ-ray background (EGRB) are complicated by a strong Galactic foreground. Estimates of the EGRB flux and spectrum, obtained by modeling the Galactic emission, have produced a variety of (sometimes conflicting) results. The latest analysis of the EGRET data found an isotropic flux I x = 1.45 ± 0.05 above 100 MeV, in units of 10 −5 ph s −1 cm −2 sr −1 . We analyze the EGRET data in search for robust constraints on the EGRB flux, finding the γ-ray sky strongly dominated by Galactic foreground even at high latitudes, with no conclusive evidence for an additional isotropic component. The γ-ray intensity measured towards the Galactic poles is similar to or lower than previous estimates of I x , even before Galactic foreground subtraction. The high latitude profile of the γ-ray data is disk-like for 40 • |b| 70 • , and even steeper for |b| 70 • ; overall it exhibits strong Galactic features and is well fit by a simple Galactic model. Based on the |b| > 40 • data we find that I x < 0.5 at a 99% confidence level, with evidence for a much lower flux. We show that correlations with Galactic tracers, previously used to identify the Galactic foreground and estimate I x , are not satisfactory; the results depend on the tracers used and on the part of the sky examined, because the Galactic emission is not linear in the Galactic tracers, and exhibits spectral variations across the sky. The low EGRB flux favored by our analysis places stringent limits on extragalactic scenarios involving γ-ray emission, such as radiation from blazars, intergalactic shocks and production of ultra-high energy cosmic rays and neutrinos. We suggest methods by which future γ-ray missions such as GLAST and AGILE could indirectly identify the EGRB.

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“…It is now known that the distribution of this gas dominates at high z (scale height i kpc) and contributes about 89 of the column density at the pole (Reynolds, 1990(Reynolds, , 199 la, b, 1993Cordes et aL, 1991). It is now known that the distribution of this gas dominates at high z (scale height i kpc) and contributes about 89 of the column density at the pole (Reynolds, 1990(Reynolds, , 199 la, b, 1993Cordes et aL, 1991).…”

Section: Emissivity Gradients and Cosmic-ray Sourcesmentioning

confidence: 99%

“…In the hard X-ray range pre-CGRO measurements are available from HEAO-1 (Peterson et al, 1990), GRIS (Gehrels and Tueller 1992); a study using the tertiary optics of the SIGMA coded mask telescope (Claret et aL, 1995) has also provided useful information. In the hard X-ray range pre-CGRO measurements are available from HEAO-1 (Peterson et al, 1990), GRIS (Gehrels and Tueller 1992); a study using the tertiary optics of the SIGMA coded mask telescope (Claret et aL, 1995) has also provided useful information.…”

Section: Energy Range 50 Kev-1 Mevmentioning

confidence: 99%

Diffuse galactic gamma-ray continuum emission

Strong

1996

Space Sci Rev

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Some of the most important questions about the diffuse gamma-ray continuum emission from the Galaxy are reviewed, based on Compton Observatory (CGRO) results, especially COMPTEL and EGRET, and also earlier COS-B analyses. The key issues include the r61e of emission from cosmic-ray interactions with molecular hydrogen and its energy dependence, emissivity gradients and their interpretation, the cosmic-ray electron spectrum and the effect of discrete sources. The relative contribution of the various emission processes at low and high latitudes is estimated and a plausible synthesis of the observed spectrum over 5 decades of energy is presented. In the energy range above 30 MeV, models based either on explicit cosmic-ray gradients or cosmic-ray/gas coupling can give acceptable fits to the data, and a clear distinction has yet to be made. The quality of the EGRET data may make this possible in the future. The value of the CO-to-H2 conversion factor from "y-rays is still uncertain and there is considerable evidence for cloud-to-cloud variations. The existence of a small emissivity gradient is well established, but is difficult to explain in a diffusive cosmic-ray propagation picture with sources distributed like SNR or pulsars unless there is a larger halo than suggested by cosmic-ray composition studies. In" the energy range 1-30 MeV covered by COMPTEL the spectrum of the diffuse emission has been measured and is consistent with a combination of bremsstrahlung and inverse-Compton emission; spatial analysis shows strong evidence for a component with a wide latitude extent which is plausibly identified with the inverse-Compton component. The molecular hydrogen appears to be only a weak 7-ray emitter at low energies, which can be interpreted in terms of reduced MeV cosmic-ray electron density in molecular clouds. New data on the hard X-ray diffuse galactic emission is becoming available and indicates the need for a low-energy upturn in the electron spectrum or some other~additional component. The contribution of unresolved sources to the 'diffuse' emission is unknown'b2a--probably lies in the range 10-20%. At high latitudes the galactic emission is intense enough to significantly complicate the identification of the extragalactic component; in particular the inverse-Compton emission from a halo a few kpc in extent can account for much of the high-latitude galactic emission. The detection of the Large Magellanic Cloud and the non-detection of the Small Magellanic Cloud provide constraints on extragalactic cosmic-rays, and provide an interesting comparison with the properties of the galactic system. On account of the large amount of data from CGRO now available, this is a subject in rapid development, and this paper provides a snapshot of the situation around mid-1995.

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The interstellar radiation field: a datum for cosmic ray physics

Cited by 25 publications

References 11 publications

High-energy Gamma Rays from the Milky Way: Three-dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities in the Interstellar Medium

High-energy Gamma Rays from the Milky Way: Three-dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities in the Interstellar Medium

The case for a low extragalactic gamma-ray background

Diffuse galactic gamma-ray continuum emission

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