In this paper, the possibility of periodic pulsar-like gamma-ray emission from the white dwarfs in AE Aquarii and AR Scorpii is investigated. We show that the white dwarf magnetospheres in AE Aquarii and AR Scorpii can possibly induce potentials to accelerate charged particles to energies in excess of one tera electronvolt (TeV) with associated gamma-ray emission through processes such as curvature radiation, inverse Compton, and hadronic processes such as neutral pion decay. We report here pulsed gamma-ray signatures at or close to the spin period of white dwarfs in both AE Aquarii and AR Scorpii in the Fermi-LAT dataset. This may indicate that both these white dwarfs possibly contain a particle accelerator that can produce relativistic electrons and ions and associated high energy radiation. The possibility of pair production is also investigated, which could provide a source for relativistic e± pairs in the magnetosphere. This could possibly be a driver for other forms of lepton-induced multi-wavelength pulsar-like emission from these two systems as well, for example, to explain the recently detected pulsed radio emission from AE Aquarii and R Scorpii in MeerKAT observations at the spin period of the white dwarf. The possibility of future detection of AE Aquarii and AR Scorpii with the Cherenkov Telescope Array (CTA) is also discussed. The future Vera Rubin Observatory will make a revolutionary contribution to time-domain astrophysics, which may lead to the discovery of thousands of new transient sources, possibly also many more close binaries with highly spun-up magnetized white dwarfs such as AE Aquarii and AR Scorpii for future investigation.
We present the preliminary results of the search for gamma−ray emission from the novalike variable AE Aquarii using the upgraded Fermi−LAT Pass 8 data set. A previous study using the Fermi−LAT Pass 7 data pipeline showed indications of a low−level, but consistent, pulsed emission at a period of 16.54 s, which is the first harmonic of the 33.08 s spin period of the white dwarf. Here we report our findings of a follow−up study utilizing the Pass 8 data, which uses an improved galactic diffuse gamma−ray emission model as well as more inclusive selection criteria. Thus far no clear detection of any significant gamma−ray excess from AE Aqr in the Fermi−LAT energy range has been made. However, there are some energy bins with significance just above 2σ. This significance value is below the Fermi−LAT detection limit that signifies a clear 4−5 σ detection and can only be considered as a 2 σ upper−limit. The corresponding upper limit of the integrated energy flux above 100 MeV is F γ ∼ 4×10 −13 erg cm −2 s −1 which is determined at the 99.995 % confidence level. However, indications of low−level pulsed modulation is found at, or close to, the 33.08 s spin period of the white dwarf in a few two−week data sections with higher than average TS values, which is promising for possible future follow−up studies with the Cherenkov Telescope Array.
Here we present the first report of pulsed emission at the spin period of the white dwarf in MeerKAT data, which is also the first report of pulsed emission at the spin period of the white dwarf in radio frequencies (L−Band). Further support for the pulsar−like behaviour of AE Aquarii is the detection of pulsed emission at the spin period of the white dwarf in AE Aquarii in Fermi−LAT data. By isolating data sections that show emission above the 2 σ level our periodicity analysis reveal clear indications of pulsed emission at the spin period of the white dwarf and its associated second harmonic (first overtone), which implies particle acceleration from both poles of the white dwarf. The detection of pulsed emission in Fermi−LAT data mimic to a large extent the emission profiles detected in very high energy gamma−ray observations made by two independent groups at Pothefstroom and Durham in the late 1980's to early 1990's. Furthermore, Fermi−LAT data sections that were observed simultaneously with optical flares show clear pulsed emission patterns at the spin period of the white dwarf similar to those reported in the late 1980's. The results presented here confirm AE Aquarii as a transient gamma−ray source with clear indications of spectral hardening during periods with enhanced gamma−ray activity. It is also shown that AE Aquarii may be detectable with CTA. A strategy is presented on how detectable pulsed emission may be extracted from the data.
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