Context. A number of novae have been found to emit high-energy gamma rays (>100 MeV). However, the origin of this emission is not yet understood. We report on the search for gamma-ray emission from 75 optically-detected Galactic novae in the first 7.4 years of operation of the Fermi Large Area Telescope using the Pass 8 data set. Aims. We compile an optical nova catalog including light curves from various resources and estimate the optical peak time and optical peak magnitude in order to search

more »

... for gamma-ray emission to test if all novae are gamma-ray emitters. Methods. We repeat the analysis of the six novae previously identified as gamma-ray sources and develop a unified analysis strategy which we then apply to all novae in our catalog. We search for emission in a 15-day time window in two-day steps ranging from 20 days before to 20 days after the optical peak time. We perform a population study with Monte Carlo simulations to set constraints on the properties of the gamma-ray emission of novae. Results. Two new novae candidates have been found at 2sigma global significance. Although these two novae candidates were not detected at a significant level individually, taking them together with the other non-detected novae, we found a sub-threshold nova population with a cumulative 3sigma significance. We report the measured gamma-ray flux for detected sources and flux upper limits for novae without significant detection. Our results can be reproduced by several gamma-ray emissivity models (e.g. a power-law distribution with a slope of 2), while a constant emissivity model (i.e. assuming novae are standard candles) can be rejected.