Probing the nova shock physics with future gamma-ray observations of the upcoming outburst from T Coronae Borealis

Abstract

Nova shocks behave like scaled-down supernova remnant shocks with a lifetime of only a few weeks or months, thereby providing a unique opportunity to study the dynamics of non-relativistic shocks as well as the shock acceleration physics. Recently, GeV and TeV gamma-ray emissions from an outburst of the recurrent nova RS Ophiuchi have been observed. The light curves of the gamma-ray emissions suggest that they arise from an external shock, which is formed as the nova ejecta interacts with the ambient medium. The shock is thought to transition from an adiabatic shock to a radiative one at later times, but no such later observations are available for RS Ophiuchi. The spectral evolution of the gamma-ray outburst of RS Ophiuchi was not well measured, and hence the related particle acceleration mechanisms are not well understood. T Coronae Borealis (T CrB) is another recurrent nova in Milky Way and its last outburst was nearly ten times optically brighter than RS Ophiuchi. Recently the optical light curve of T CrB displayed a state transition behavior before the eruption, and it has been predicted that T CrB will undergo an outburst in the near future. By performing a theoretical investigation, we find that Fermi-LAT could probably capture the transition of the shock from the adiabatic phase to the radiative phase at the GeV band if the ambient wind medium is dense with $A_{\star}\geq1$. Due to its higher brightness, we also find that imaging atmospheric Cherenkov telescopes such as MAGIC and VERITAS, and extensive air shower experiments such as LHAASO could detect the nova outburst and measure the gamma-ray spectrum in the very-high-energy ($>0.1\,{\rm TeV}$) band more precisely. This can be used to constrain the high-energy cutoff index in the accelerated proton spectrum and the acceleration efficiency, which will shed light on the particle acceleration physics in nova shocks.