TeV $\gamma$ Rays from Photodisintegration and Daughter Deexcitation of Cosmic-Ray Nuclei

It is commonly assumed that high-energy $\gamma$ rays are made via either purely electromagnetic processes or the hadronic process of pion production, followed by decay. We investigate astrophysical contexts where a third process ($A^{*}$) would dominate: namely, the photodisintegration of highly boosted nuclei followed by daughter deexcitation. Starburst regions such as Cygnus OB2 appear to be promising sites for TeV $\gamma$-ray emission via this mechanism. A unique feature of the $A^{*}$ process is a sharp flattening of the energy spectrum below $\sim 10\mathrm{TeV}/(T/\mathrm{eV})$ for $\gamma$-ray emission from a thermal region of temperature $T$. The $A^{*}$ mechanism described herein offers an important contribution to $\gamma$-ray astronomy in the era of intense observational activity.

Figure 1

The scaling functions $f(w)$ and $x_{ϵ}^{2}F(x_{ϵ})$, proportional to the photodissociation rate in Eq. (4) and the $\gamma$-ray ${ϵ}^{2}dF/dϵ$ spectrum in Eq. (8), respectively.