COSMIC-RAY HELIUM HARDENING

Journal Article · Tue Mar 01 04:00:00 EST 2011 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/729/1/L13· OSTI ID:21560460

Ohira, Yutaka; Ioka, Kunihito ^[1]

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1. Theory Center, Institute of Particle and Nuclear Studies, KEK (High Energy Accelerator Research Organization), 1-1 Oho, Tsukuba 305-0801 (Japan)

Recent observations by the CREAM and ATIC-2 experiments suggest that (1) the spectrum of cosmic-ray (CR) helium is harder than that of CR protons below the knee energy, 10{sup 15}eV, and (2) all CR spectra become hard at {approx}>10{sup 11}eV nucleon{sup -1}. We propose a new idea, that higher energy CRs are generated in a more helium-rich region, to explain the hardening without introducing different sources for CR helium. The helium-to-proton ratio at {approx}100 TeV exceeds the Big Bang abundance Y = 0.25 by several times, and the different spectrum is not reproduced within the diffusive shock acceleration theory. We argue that CRs are produced in a chemically enriched region, such as a superbubble, and the outward-decreasing abundance naturally leads to the hard spectrum of CR helium if CRs escape from the supernova remnant shock in an energy-dependent way. We provide a simple analytical spectrum that also fits well the hardening due to the decreasing Mach number in the hot superbubble with {approx}10{sup 6} K. Our model predicts hard and concave spectra for heavier CR elements.

• OSTI ID: 21560460
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 729; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCELERATION
BARYONS
COSMIC RADIATION
COSMIC RADIO SOURCES
ELEMENTARY PARTICLES
ELEMENTS
ENERGY DEPENDENCE
FERMIONS
FLUIDS
GASES
HADRONS
HELIUM
IONIZING RADIATIONS
NONMETALS
NUCLEONS
PARTICLES
PROTONS
RADIATIONS
RARE GASES
SHOCK WAVES
SUPERNOVA REMNANTS