The extreme coronal line emitter AT 2022fpx: Varying optical polarization properties and late-time X-ray flare
arxiv(2024)
摘要
Supermassive black holes have been known to disrupt passing stars, producing
outbursts called tidal disruption events (TDEs). TDEs have recently gained
attention due to their unique dynamics and emission processes, which are still
not fully understood. Especially, the so-called optical TDEs, are of interest
as they often exhibit delayed or obscured X-ray emission from the accretion
disk, making the origin of the prompt emission unclear. In this paper, we
present the optical photo-, spectro-, and polarimetry of a recent TDE candidate
AT 2022fpx, in addition to accompanying monitoring observations in ultraviolet
and X-rays. The optical spectra of AT 2022fpx show Bowen fluorescence as well
as highly-ionized iron emission lines, which are characteristic of extreme
coronal line emitters. Additionally, the source exhibits variable but
low-polarized emission at the outburst peak, with a clear rotation of the
polarization angle. X-ray emission observed later in the decay appear
flare-like but is consistent with constant temperature black-body emission. The
overall outburst decay is slower than for typical TDEs, and resembles more the
ones seen from Bowen fluorescence flares. These observations suggest that AT
2022fpx could be a key source in linking different long-lived TDE scenarios.
Its unique characteristics, such as the extreme coronal line emission, variable
polarization, and the delayed X-ray flare, can be attributed to the outer shock
scenario or a clumpy torus surrounding the supermassive black hole. Further
studies, especially in the context of multi-wavelength observations, are
crucial to fully understand the dynamics and emission mechanisms of these
intriguing astrophysical events.
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