Detection of renewed radio activity from Cygnus X-3 with the Nasu radio telescope array at 1.4 GHz

ATel #18003; K. Tsubono (Univ. Tokyo), K. Asuma (Kawaguchi-Kita High School), K. Niinuma (Yamaguchi Univ.), K. Takefuji (JAXA) and T. Daishido (Waseda Univ.)
on 24 Aug 2026; 07:20 UT
Credential Certification: Kimio Tsubono (tsubono@phys.s.u-tokyo.ac.jp)

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We report the detection of renewed radio activity from the X-ray binary Cygnus X-3 with the Nasu radio telescope array at 1.4 GHz.

Cygnus X-3 was below the Nasu detection limit of approximately 200 mJy in our observations on MJD 61265 and 61266. The source was first detected on MJD 61268 with a flux density of approximately 2.0 Jy and increased to 2.3 Jy on the following day. The radio emission subsequently decreased to about 0.5 Jy on MJD 61271-61272 before increasing again. In our latest observation on 2026 August 22 UT (MJD 61274), the source reached a flux density of 4.3 ± 0.1 Jy at 1.4 GHz, indicating that the radio activity is still evolving.

The Nasu radio telescope array observes Cygnus X-3 once per day at its culmination. Consequently, the onset time of the present radio activity is constrained to within approximately one day. Continued monitoring will determine whether the source develops into a major radio flare.

A preliminary 1.4 GHz light curve is available here.

Continued monitoring will be carried out to search for renewed radio activity from this source.

The Nasu telescope array is a spatial fast Fourier transform (FFT) interferometer consisting of eight linearly aligned antennas with 20 m spherical dishes. This type of interferometer was developed to survey transient radio sources, providing an angular resolution comparable to that of a 160 m dish and a field of view equivalent to that of a 20 m dish.

Nasu telescope array HP:
https://nasu-radio-telescope.jp