Hard X-ray emissions from Cassiopeia A observed by INTEGRAL

Abstract

Cassiopeia A (Cas A) as the nearby young remnant of a core-collapse supernova is the best candidate for astrophysical studies in supernova explosion and its environment. We studied hard X-ray emissions from Cas A using the ten-year data of INTEGRAL observations, and first detected non-thermal continuum emission from the source up to 220 keV. The ${}^{44}$Ti line emissions at 68 and 78 keV are confirmed by our observations with a mean flux of $\sim (2.2\pm 0.4)\times 10^{-5}$ ph cm${}^{-2}$ s${}^{-1}$, corresponding to a ${}^{44}$Ti yield in Cas A of $(1.3\pm 0.4)\times 10^{-4}$ \ms. The continuum emission from 3 -- 500 keV can be fitted with a thermal bremsstrahlung of $kT\sim 0.79\pm 0.08$ keV plus a power-law model of $\Gamma \sim 3.13\pm 0.03$. The non-thermal emission from Cas A is well fitted with a power-law model without a cutoff up to 220 keV. This radiation characteristic is inconsistent with the diffusive shock acceleration models with the remnant shock velocity of only 5000km s${}^{-1}$. The central compact object in Cas A cannot contribute to the emission above 80 keV significantly. Some possible physical origins of the non-thermal emission above 80 keV from the remnant shock are discussed. We deduce that the asymmetrical supernova explosion scenario of Cas A is a promising scenario to produce high energy synchrotron radiation photons, where a part of ejecta with the velocity of $\sim 0.1c$ and opening angle of $\sim 10^{\circ }$ can account for the 100-keV emission, consistent with the "jet" observed in Cas A.

arXiv comment20 pages, 6 figures, 2 tables; accepted for the publication in ApJ

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• Evidence for proton acceleration up to TeV energies based on VERITAS and Fermi-LAT observations of the Cas A SNR
• The mass, location and heating of the dust in the Cassiopeia A supernova remnant
• Dust destruction and survival in the Cassiopeia A reverse shock
• Time evolution of broadband non-thermal emission from supernova remnants in different circumstellar environments
• Sensitivity of ${}^{44}$Ti and ${}^{56}$Ni production in CCSN shock-driven nucleosynthesis to reaction rates
• Is Supernova Remnant Cassiopeia A a PeVatron?
• Comparison of simulated backgrounds with in-orbit observations for HE, ME and LE onboard Insight-HXMT
• An Asymmetrical Model for High Energy Radiation of Cassiopeia A