A Fermi Large Area Telescope analysis unveils possible gamma-ray emission in magnetic cataclysmic variable systems and highly magnetised isolated white dwarfs.

Abstract

We searched for gamma-ray emission from magnetic cataclysmic variable (MCV) systems, and highly magnetised isolated white dwarfs, using the data observed by the \textit{Fermi} Large Area Telescope (LAT). A total of 75 sources (19 polars, 24 intermediate polars, 6 solitary white dwarfs, 3 double white dwarfs, 18 DQ white dwarfs, 3 DQ Hers, and 2 white dwarf pulsars) were analysed, with a primary focus on those displaying strong magnetic activity and having short orbital periods or white dwarfs with short spin periods. The preliminary results of binned-likelihood analysis in the energy range 0.05-20 GeV revealed 28 sources above the LAT detection level, indicating the presence of gamma-ray emission in these systems. The search for periodic emission in the same energy range in ZTF J153932.16+502738.8 and SDSS J103655.39+652252.2 reveals gamma-ray emissions modulated to the orbital period (6.91 minutes) of ZTF J153932.16+502738.8, with a significance of 5.3 $\sigma$, and pulses nearly synchronised with a period of 1115.64751 seconds in SDSS J103655.39+652252.2, with a significance of 5.4 $\sigma$. This study provides observational evidence that MCVs with short spin/orbital periods are potential gamma-ray sources. The observed gamma-ray signals provide valuable insights into the underlying physical processes at work in these enigmatic binary systems such as particle acceleration and gamma ray production.