Cosmic-rays and diffuse γ-rays: Spatial gradients of Galactic parameters

Shibata, T.; Honda, N.; Watanabe, J.

doi:10.1016/j.astropartphys.2007.01.003

Cited by 13 publications

(11 citation statements)

References 59 publications

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“…This would mean that SNRs, or CR source classes having a similar spatial distribution as the proxies considered in this paper, are not the only source of CRs (Butt 2009). Modifications of the CR propagation mechanism have also been proposed in the literature as an explanation for increased CR flux in the outer Galaxy (Breitschwerdt et al 2002;Shibata et al 2007). Alternatively, large amounts of gas not traced by 21 cm emitting H i and CO (as the tracer of H 2 ) surveys may be present in the outer Galaxy (Papadopoulos et al 2002), which would also increase the γ -ray emission.…”

Section: Discussionmentioning

confidence: 90%

FERMI-LAT OBSERVATIONS OF THE DIFFUSE γ-RAY EMISSION: IMPLICATIONS FOR COSMIC RAYS AND THE INTERSTELLAR MEDIUM

Ackermann¹,

Ajello²,

Atwood³

et al. 2012

ApJ

669

763

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Section: Discussionmentioning

confidence: 90%

FERMI-LAT OBSERVATIONS OF THE DIFFUSE γ-RAY EMISSION: IMPLICATIONS FOR COSMIC RAYS AND THE INTERSTELLAR MEDIUM

Ackermann¹,

Ajello²,

Atwood³

et al. 2012

ApJ

669

763

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“…Uhlig et al (2012) note that CR-driven winds could also suppress the star formation rate by a significant factor. Shibata et al (2007) proposed a non-uniform diffusion coefficient that increases with Galactocentric radius and distance from the Galactic plane. Indeed, models with a large Galactic halo, and thus faster CR diffusion, are able to better reproduce the γ-ray emissivity in the outer Galaxy (Ackermann et al 2012d).…”

Section: Gradients Of Cosmic-ray Spectra Across the Galaxymentioning

confidence: 99%

Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data

Acero

Ackermann

Ajello

et al. 2016

ApJS

415

349

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Most of the celestial γ rays detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays interact with interstellar nucleons and photons. Conventional point-source and extended-source studies rely on the modeling of this diffuse emission for accurate characterization. Here, we describe the development of the Galactic Interstellar Emission Model (GIEM), which is the standard adopted by the LAT Collaboration and is publicly available. This model is based on a linear combination of maps for interstellar gas column density in Galactocentric annuli and for the inverse-Compton emission produced in the Galaxy. In the GIEM, we also include large-scale structures like LoopI and the Fermi bubbles. The measured gas emissivity spectra confirm that the cosmic-ray proton density decreases with Galactocentric distance beyond 5 kpc from the Galactic Center. The measurements also suggest a softening of the proton spectrum with Galactocentric distance. We observe that the Fermi bubbles have boundaries with a shape similar to a catenary at latitudes below 20°and we observe an enhanced emission toward their base extending in the north and south Galactic directions and located within ∼4°of the Galactic Center.

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“…Bloemen et al (1993) suggested that the radial distribution of CR sources derived from observations may be biased and their real distribution is flatter or the diffusion parameters derived from the local CR measurements are not the same throughout the Galaxy. Solutions to this issue in terms of CR propagation phenomenology have been proposed: CRdriven Galactic winds and anisotropic diffusion (Breitschwerdt et al 2002), or non-uniform diffusion coefficient that increases with Galactocentric radius and the distance from the Galactic plane (Shibata et al 2007).…”

mentioning

confidence: 99%

FERMI-LAT OBSERVATIONS OF HIGH-ENERGY Γ-Ray EMISSION TOWARD THE GALACTIC CENTER

Ajello

Albert

Atwood

et al. 2016

ApJ

395

488

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The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission towards the Galactic centre (GC) in high-energy γ-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1 − 100 GeV from a 15 • × 15 • region about the direction of the GC, and implications for the interstellar emissions produced by cosmic ray (CR) particles interacting with the gas and radiation fields in the inner Galaxy and for the point sources detected. Specialised interstellar emission models (IEMs) are constructed that enable separation of the γ-ray emission from the inner ∼ 1 kpc about the GC from the fore-and background emission from the Galaxy. Based on these models, the interstellar emission from CR electrons interacting with the interstellar radiation field via the inverse Compton (IC) process and CR nuclei inelastically scattering off the gas producing γ-rays via π 0 decays from the inner ∼ 1 kpc is determined. The IC contribution is found to be dominant in the region and strongly enhanced compared to previous studies. A catalog of point sources for the 15 • × 15 • region is self-consistently constructed using these IEMs: the First Fermi-LAT Inner Galaxy point source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with γ-ray point sources over the same region taken from existing catalogs, including the Third Fermi-LAT Source Catalog (3FGL). In general, the spatial density of 1FIG sources differs from those in the 3FGL, which is attributed to the different treatments of the interstellar emission and energy ranges used by the respective analyses. Three 1FIG sources are found to spatially overlap with supernova remnants (SNRs) listed in Green's SNR catalog; these SNRs have not previously been associated with high-energy γ-ray sources. Most 3FGL sources with known multi-wavelength counterparts are also found. However, the majority of 1FIG point sources are unassociated. After subtracting the interstellar emission and point-source contributions from the data a residual is found that is a sub-dominant fraction of the total flux. But, it is brighter than the γ-ray emission associated with interstellar gas in the inner ∼ 1 kpc derived for the IEMs used in this paper, and comparable to the integrated brightness of the point sources in the region for energies 3 GeV. If spatial templates that peak toward the GC are used to model the positive residual and included in the total model for the 15 • ×15 • region, the agreement with the data improves, but they do not account for all the residual structure. The spectrum of the positive residual modelled with these templates has a strong dependence on the choice of IEM.

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Cosmic-rays and diffuse γ-rays: Spatial gradients of Galactic parameters

Cited by 13 publications

References 59 publications

FERMI-LAT OBSERVATIONS OF THE DIFFUSE γ-RAY EMISSION: IMPLICATIONS FOR COSMIC RAYS AND THE INTERSTELLAR MEDIUM

FERMI-LAT OBSERVATIONS OF THE DIFFUSE γ-RAY EMISSION: IMPLICATIONS FOR COSMIC RAYS AND THE INTERSTELLAR MEDIUM

Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data

FERMI-LAT OBSERVATIONS OF HIGH-ENERGY Γ-Ray EMISSION TOWARD THE GALACTIC CENTER

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