Evidence for Gamma-Ray Pulsations from the Classical Nova ASASSN-16ma

TL;DR

This paper reports the discovery of coherent gamma-ray pulsations from the classical nova ASASSN-16ma, indicating the white dwarf's spin period and suggesting potential optical pulsations for future studies.

Contribution

First detection of gamma-ray pulsations from a classical nova, revealing the white dwarf's spin period and opening new avenues for understanding nova mechanisms.

Findings

Gamma-ray pulsations at 544.84 seconds detected during nova outburst

Significance level of 4.0 sigma for the pulsation detection

Steady pulsations over 4 days, indicating a white dwarf spin signal

Abstract

We report here a new result extracted from the Fermi Large Area Telescope observation of the classical nova ASASSN-16ma that exhibits coherent gamma-ray pulsations at 544.84(7) seconds during its outburst in 2016. Considering the number of independent trials, the significance of the evidence is 4.0 sigma, equivalent to a false alarm probability of 5.9e-5. The periodicity was steady during the 4 days of its appearance, indicating its origin as the spinning signal of the white dwarf. Given that the optical and gamma-ray light curves of some shock-powered gamma-ray novae have been recently shown closely correlated to each other, the gamma-ray pulsation phenomenon likely implies an existence of the associated optical pulsations, which would provide detailed ephemerides for these extreme white dwarf binaries for further investigations in the near future.