Multi-wavelength Study for Gamma-Ray Nova V1405 Cas

Abstract Novae are found to have GeV to TeV γ -ray emission, which reveals the shock acceleration from the white dwarfs. Recently, V1405 Cas was reported to radiate suspicious γ -ray by Fermi-LAT with low significance (4.1 σ ) 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 a continuous search for GeV γ -ray from Fermi-LAT. No γ -ray was found. For V1405 Cas the flux level is lower than other well-studied Fermi novae, and the γ -ray maximum appears at t 0 + 145 days. γ -ray of V1405 Cas is used to search potential γ -ray periodicity. No γ -ray periodicity was found during the time of observation. By comparing multi-wavelength data, the γ -ray upper limit to optical flux ratio with a value at around 10 −4 is obtained to constrain the shock acceleration. Long-term analysis from 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.