Wei Wang¹ and Zhuo Li^2,3

¹National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, China
²Department of Astronomy and Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China
³Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650011, China

A deep hard X-ray survey of the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite has detected for the first time non-thermal emission up to 90 keV in the Tycho supernova (SN) remnant. Its 3–100 keV spectrum is fitted with a thermal bremsstrahlung of kT ~ 0.81 ± 0.45 keV plus a power-law model of Γ ~ 3.01 ± 0.16. Based on diffusive shock acceleration theory, this non-thermal emission, together with radio measurements, implies that the Tycho remnant may not accelerate protons up to >PeV but to hundreds TeV. Only heavier nuclei may be accelerated to the cosmic ray spectral “knee.” In addition, using INTEGRAL, we search for soft gamma-ray lines at 67.9 and 78.4 keV that come from the decay of radioactive ⁴⁴Ti in the Tycho remnant. A bump feature in the 60–90 keV energy band, potentially associated with the ⁴⁴Ti line emission, is found with a marginal significance level of ~2.6σ. The corresponding 3σ upper limit on the ⁴⁴Ti line flux amounts to 1.5 × 10^-5 photon cm^-2 s^-1. Implications on the progenitor of the Tycho SN, considered to be a Type Ia SN prototype, are discussed.

Reference
Wang W and Li Z (2014) Hard X-ray emission and 44Ti line features of the Tyco supernova remnant . The Astrophysical Journal 189:123.
[doi:10.1088/0004-637X/789/2/123]

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