Multi-wavelength study for gamma-ray nova V1405 Cas

Abstract

Novae are found to have GeV to TeV gamma-ray emission, which reveals the shock acceleration from the white dwarfs. Recently, V1405 Cas was reported to radiated suspicious gamma-ray by \textit{Fermi}-LAT with low significance ($4.1 \sigma$) after the optical maximum. Radio observations reveal that it is one of the five brightest novae surrounded by low-density ionized gas columns. Here we report continuous search for GeV gamma-ray from \textit{Fermi}-LAT. No gamma-ray were found. For V1405 Cas, the flux level is lower than other well-studied \textit{Fermi} novae, and the gamma-ray maximum appear at $t_{0} + 145$ d. Gamma-ray of V1405 Cas are used to search potential gamma-ray periodicity. No gamma-ray periodicity was found during the time of observation. By comparing multi-wavelength data, the gamma-ray upper limit to optical flux ratio with value at around $10^{-4}$ is obtained to constrain the shock acceleration. Long-term analysis from \textit{Swift}-XRT gets X-ray spectral in the post-shock phase, which indicates that V1405 Cas became a super-soft source. The best-fit black body temperature at the super soft state is 0.11 - 0.19 keV.