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A tidal disruption event (TDE) occurs when a star passes too close to
a supermassive black hole (SMBH) and gets torn apart by the tidal
forces exerted on it by the SMBH. About half of the disrupted star
falls back to the SMBH and generates a multi-wavelength flare. A
discovery in several recent TDEs is the onset of late-time delayed
radio flares, with the TDE AT2018hyz, which exhibited a delayed radio
flare almost three years after the stellar disruption, the latest
example.
Sfaradi et al. report new radio observations of this TDE with the
ATCA and the Arcminute Microkelvin Imager - Large Array (AMI-LA),
spanning from a month to more than four years after the optical
discovery. The fast-rising, delayed, radio flare continues to rise
almost ~1580 days after the optical discovery. The authors present an
off-axis jet model that can explain the full set of radio
observations, invoking a powerful narrow jet with an opening angle of
∼7 degrees and a relatively large viewing angle of ∼42 degrees,
launched at the time of the stellar disruption. They provide
predictions based on the model for the light curve turnover time, and
for the proper motion of the radio emitting source. The plots above
show at left the 15.5 GHz light curve of AT 2018hyz with AMI-LA, with
triangles marking 3𝜎 upper limits. Also marked are the times of the
first radio detection of the flare, and of the last reported
observation. The plot at the right shows the radio spectrum, between
4.7 and 17.5 GHz, obtained with ATCA 1290 days after optical
discovery.
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