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.
The nova-like variable AE Aquarii has been continuously studied since its discovery on photographic plates in 1934. In this short review the peculiar multi-wavelength properties of AE Aquarii will be reviewed and explained in context of its evolution from a high mass transfer phase, during which period it could have been a supersoft X-ray source (SSS).
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