Results from the long-term Fermi-LAT observations of the white dwarf binary pulsar AR Scorpii

Q. Kaplan; P. J. Meintjes; K. K. Singh; H. J. van Heerden; F. A. Ramamonjisoa; I. P. van der Westhuizen

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arXiv · 1908.00283

Results from the long-term Fermi-LAT observations of the white dwarf binary pulsar AR Scorpii

Q. Kaplan·P. J. Meintjes·K. K. Singh·H. J. van Heerden·F. A. Ramamonjisoa·I. P. van der Westhuizen

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Abstract

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 ($P_{*} = 117 \, \mbox{s}$) as well as a beat period ($P_{\rm b} = 118.1 \, \mbox{s}$) 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 analysis 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 $\sqrt{TS}\leq$ 3.87$\sigma$ for the integrated gamma-ray activity between 100 MeV - 500 GeV at a photon flux level of 0.486 $\pm$ 0.261 x 10$^{-8}$ photons cm$^{-2}$ s$^{-1}$ using the broken power law model. This resulted in a 3$\sigma$ 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 location that coincides with the position of AR Sco.

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Q. Kaplan, P. J. Meintjes, K. K. Singh, H. J. van Heerden, F. A. Ramamonjisoa, I. P. van der Westhuizen. 2019-08-01. Results from the long-term Fermi-LAT observations of the white dwarf binary pulsar AR Scorpii. https://arxiv.org/abs/1908.00283

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