# Hard X-Ray Emission and $^44$Ti Line Features of the Tycho Supernova Remnant

 Title Hard X-Ray Emission and $^44$Ti Line Features of the Tycho Supernova Remnant Publication Type Journal Article Year of Publication 2014 Authors Wang, W, Li, Z Journal \apj Volume 789 Pagination 123 Keywords cosmic rays, gamma rays: ISM, ISM: supernova remnants, supernovae: individual: Tycho Abstract {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 {\plusmn} 0.45 keV plus a power-law model of {$\Gamma$} \~{} 3.01 {\plusmn} 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 {\gt}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 $^{44}$Ti in the Tycho remnant. A bump feature in the 60-90 keV energy band, potentially associated with the $^{44}$Ti line emission, is found with a marginal significance level of \~{}2.6{$\sigma$}. The corresponding 3{$\sigma$} upper limit on the $^{44}$Ti line flux amounts to 1.5 {\times} 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. } DOI 10.1088/0004-637X/789/2/123