The ASKAP scans at 888MHz. From the paper, which luckily is publicly available:
> It exhibited
a high degree (∼ 25%) of circular polarization when it was visible. We monitored the source with
the MeerKAT telescope from 2020 November to 2021 February on a 2–4 week cadence. The source
was not detected with MeerKAT before 2021 February 07 when it appeared and reached a peak
flux density of 5.6 mJy. The source was still highly circularly polarized, but also showed up to 80%
linear polarization, and then faded rapidly with a timescale of one day. The rotation measure of the
source varied significantly, from −11.8±0.8 rad m−2
to −64.0±1.5 rad m−2
, over three days. No X-ray
counterpart was found in follow-up Swift or Chandra observations about a week after the first MeerKAT
detection, with upper limits of ∼ 5.0 × 1031 erg s−1
(0.3–8 keV, assuming a distance ∼ 10 kpc). No
counterpart is seen in new or archival near-infrared observations down to J = 20.8 mag.
> It exhibited a high degree (∼ 25%) of circular polarization when it was visible. We monitored the source with the MeerKAT telescope from 2020 November to 2021 February on a 2–4 week cadence. The source was not detected with MeerKAT before 2021 February 07 when it appeared and reached a peak flux density of 5.6 mJy. The source was still highly circularly polarized, but also showed up to 80% linear polarization, and then faded rapidly with a timescale of one day. The rotation measure of the source varied significantly, from −11.8±0.8 rad m−2 to −64.0±1.5 rad m−2 , over three days. No X-ray counterpart was found in follow-up Swift or Chandra observations about a week after the first MeerKAT detection, with upper limits of ∼ 5.0 × 1031 erg s−1 (0.3–8 keV, assuming a distance ∼ 10 kpc). No counterpart is seen in new or archival near-infrared observations down to J = 20.8 mag.
https://arxiv.org/pdf/2109.00652.pdf