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Cosmic ray models of the ridge-like excess of gamma rays in the Galactic Centre

Macias, Oscar; Gordon, Chris; Crocker, Roland; Profumo, Stefano

Description

The High-Energy Stereoscopic System (HESS) has detected diffuse TeV emission correlated with the distribution of molecular gas along the Ridge at the Galactic Centre. Diffuse, nonthermal emission is also seen by the Fermi large area telescope (Fermi-LAT) in the GeV range and by radio telescopes in the GHz range. Additionally, there is a distinct, spherically symmetric excess of gamma rays seen by Fermi-LAT in the GeV range. A cosmic ray flare, occurring in the Galactic Centre, 104 yr ago has...[Show more]

dc.contributor.authorMacias, Oscar
dc.contributor.authorGordon, Chris
dc.contributor.authorCrocker, Roland
dc.contributor.authorProfumo, Stefano
dc.date.accessioned2016-02-24T22:40:55Z
dc.identifier.issn0035-8711
dc.identifier.urihttp://hdl.handle.net/1885/98495
dc.description.abstractThe High-Energy Stereoscopic System (HESS) has detected diffuse TeV emission correlated with the distribution of molecular gas along the Ridge at the Galactic Centre. Diffuse, nonthermal emission is also seen by the Fermi large area telescope (Fermi-LAT) in the GeV range and by radio telescopes in the GHz range. Additionally, there is a distinct, spherically symmetric excess of gamma rays seen by Fermi-LAT in the GeV range. A cosmic ray flare, occurring in the Galactic Centre, 104 yr ago has been proposed to explain the TeV Ridge. An alternative, steady-state model explaining all three data sets (TeV, GeV, and radio) invokes purely leptonic processes.We show that the flare model from the Galactic Centre also provides an acceptable fit to the GeV and radio data, provided the diffusion coefficient is energy independent. However, ifKolmogorov-type turbulence is assumed for the diffusion coefficient, we find that two flares are needed, one for the TeV data (occurring approximately 104 yr ago) and an older one for the GeV data (approximately 105 yr old).We find that the flare models we investigate do not fit the spherically symmetric GeV excess as well as the usual generalized Navarro-Frenk-White spatial profile, but are better suited to explain the Ridge.We also show that a range of single-zone, steady-state models are able to explain all three spectral data sets. Large gas densities equal to the volumetric average in the region can be accommodated by an energy-independent diffusion or streaming based steady-state model. Additionally, we investigate how the flare and steady-state models may be distinguished with future gamma-ray data looking for a spatial dependence of the gamma-ray spectral index.
dc.publisherBlackwell Publishing Ltd
dc.rightsAuthor/s retain copyright
dc.sourceMonthly Notices of the Royal Astronomical Society
dc.titleCosmic ray models of the ridge-like excess of gamma rays in the Galactic Centre
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume451
dc.date.issued2015
local.identifier.absfor020103 - Cosmology and Extragalactic Astronomy
local.identifier.absfor020104 - Galactic Astronomy
local.identifier.absfor020106 - High Energy Astrophysics; Cosmic Rays
local.identifier.ariespublicationU3488905xPUB5590
local.type.statusPublished Version
local.contributor.affiliationMacias, Oscar, University of Canterbury
local.contributor.affiliationGordon, Chris, University of Canterbury
local.contributor.affiliationCrocker, Roland, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationProfumo, Stefano, University of California
local.bibliographicCitation.issue2
local.bibliographicCitation.startpage1833
local.bibliographicCitation.lastpage1847
local.identifier.doi10.1093/mnras/stv1002
dc.date.updated2016-02-24T10:07:54Z
local.identifier.scopusID2-s2.0-84938152691
dcterms.accessRightsOpen Access
CollectionsANU Research Publications

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