The Orion Region: Evidence of enhanced cosmic-ray density in a stellar wind forward shock interaction with a high density shell

被引：5

作者：

Cardillo, M. ^{[1
]}

Marchili, N. ^{[1
]}

Piano, G. ^{[1
]}

Giuliani, A. ^{[5
]}

Tavani, M. ^{[1
,2
,3
,4
]}

Molinari, S. ^{[1
]}

机构：

[1] INAF IAPS, Via Fosso del Cavaliere 100, I-00133 Rome, Italy

[2] Univ Tor Vergata, Dip Fis, Via Ric Sci 1, I-00133 Rome, Italy

[3] Gran Sasso Sci Inst, Viale Francesco Crispi 7, I-67100 Laquila, Italy

[4] Acad Nazl Lincei, Astron, Via Lungara 10, I-00165 Rome, Italy

[5] INAF IASF Milano, Via E Bassini 15, I-20133 Milan, Italy

来源：

ASTRONOMY & ASTROPHYSICS | 2019年 / 622卷

关键词：

acceleration of particles; radiation mechanisms: non-thermal; methods: data analysis; stars:; winds; outflows; cosmic rays; gamma rays: ISM; SUPERNOVA-REMNANTS; MOLECULAR CLOUDS; EMISSION; ACCELERATION; GAS;

D O I：

10.1051/0004-6361/201833651

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

Context. In recent years, an in-depth gamma-ray analysis of the Orion region has been carried out by the AGILE and Fermi/LAT (Large Area Telescope) teams with the aim of estimating the H-2-CO conversion factor, X-CO. The comparison of the data from both satellites with models of diffuse gamma-ray Galactic emission unveiled an excess at (l, b) = [213.9, -19.5], in a region at a short angular distance from the OB star kappa-Ori. Possible explanations of this excess are scattering of the so-called "dark gas", non-linearity in the H-2-CO relation, or cosmic-ray (CR) energization at the kappa-Ori wind shock. Aims. Concerning this last hypothesis, we want to verify whether cosmic-ray acceleration or re-acceleration could be triggered at the kappa-Ori forward shock, which we suppose to be interacting with a star-forming shell detected in several wavebands and probably triggered by high energy particles. Methods. Starting from the AGILE spectrum of the detected gamma-ray excess, showed here for the first time, we developed a valid physical model for cosmic-ray energization, taking into account re-acceleration, acceleration, energy losses, and secondary electron contribution. Results. Despite the characteristic low velocity of an OB star forward shock during its "snowplow" expansion phase, we find that the Orion gamma-ray excess could be explained by re-acceleration of pre-existing cosmic rays in the interaction between the forward shock of kappa-Ori and the CO-detected, star-forming shell swept-up by the star expansion. According to our calculations, a possible contribution from freshly accelerated particles is sub-dominant with respect the re-acceleration contribution. However, a simple adiabatic compression of the shell could also explain the detected gamma-ray emission. Futher GeV and TeV observations of this region are highly recommended in order to correctly identify the real physical scenario.

引用

页数：8

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