Evidence of the gamma-ray counterpart from nova FM Cir with Fermi-LAT

Abstract

We report the analysis results of X-ray and γ-ray data of the nova FM Cir taken by Swift and Fermi-LAT. The γ-ray emission from FM Cir can be identified with a significance level of ∼ 3σ within ∼ 40 days after the nova eruption (2018 January 19) while we bin the light curve per day. The significance can further exceed 4σ confidence level if we accumulate longer time (i.e., 20 days) to bin the light curve. The γ-ray counterpart could be identified with a Test Statistic (TS) above 4 until ∼180 days after the eruption. The duration of the gamma-ray detection was longer than those reported in the previous studies of the other novae detected in the GeV range. The significant X-ray emission was observed after the gamma-ray flux level fell below the sensitivity of Fermi-LAT. The hardness ratio of the X-ray emission decreased rapidly with time, and the spectra were dominated by blackbody radiation from the hot white dwarf. Except for the longer duration of the γ-ray emission, the multi-wavelength properties of FM Cir closely resemble those of other novae detected in the GeV range.