Results form the long-term Fermi-LAT observations of the white dwarf binary pulsar AR Scorpii
July 22, 2019
The discovery of the white dwarf binary system AR Scorpii (AR Sco) with its fascinating non-thermal dominated multi-frequency emission has sparked renewed interest in potential high energy gamma-ray emission from white dwarf pulsars. The Spectral Energy Distribution (SED) below and above optical shows evidence of non-thermal synchrotron emission, with pulsed emission in optical and X-ray bands at the white dwarf spin period (P ∗ = 117 s) as well as a beat
period (P b = 118.1 s) with the binary period. From an energy perspective, the highly magnetic rotating white dwarf can accelerate particles to TeV energies. In this study, a search for high
energy gamma-ray emission was conducted between 100 MeV - 500 GeV by analysing the newly available Fermi-LAT Pass 8 data with the new Fermi 1.0.1 Science Tools. Binned likelihood anal-
ysis was done using power law, broken power law and log parabola models. From the selected Region of Interest (ROI) centred on AR Sco’s position, we calculated a significance of T S ≤ 3.87σ for the integrated gamma-ray activity between 100 MeV - 500 GeV at a photon flux level of 0.486 ± 0.261 x 10^−8 photons cm^−2 s^−1 using the broken power law model. This resulted in a 3σ upper-limit detection from the position of AR Sco. The location of AR Sco inside the
Rho Ophiuchi (Rho Oph) molecular cloud complex combined with the poor spatial resolution of Fermi-LAT, complicates any positive identification of low-level gamma-ray activity at the loca-
tion that coincides with the position of AR Sco.
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