Decay of the Cygnus X-3 radio flare observed with the Nasu radio telescope array at 1.4 GHz
ATel #17637; K. Tsubono (Univ. Tokyo), K. Asuma (Kawaguchi-Kita High School), K. Niinuma (Yamaguchi Univ.), K. Takefuji (JAXA) and T. Daishido (Waseda Univ.)
on 29 Jan 2026; 07:28 UT
Credential Certification: Kimio Tsubono (tsubono@phys.s.u-tokyo.ac.jp)
Subjects: Radio, Binary, Black Hole, Transient
Referred to by ATel #: 17661
We report continued radio monitoring of Cygnus X-3 with the Nasu radio telescope array at 1.4 GHz, following the recent radio activity reported in ATel #17600 and ATel #17605 and our subsequent detections.
The radio emission was first detected on 2026 January 16 at approximately 03:30 UT, after a prior non-detection. Since Cygnus X-3 is observed only once per day near transit with the Nasu radio telescope array, the exact onset time of the radio flare is not well constrained. The radio flux subsequently increased to a peak flux density of about 6.5 Jy on the following day.
After reaching the peak, the radio flux exhibited a monotonic decay. Our observations on 2026 January 28 indicate that the radio emission from Cygnus X-3 has faded below our detection limit of approximately 200 mJy, with no significant signal detected at the source position. This suggests that the radio flare has substantially decayed and that the source is returning to a low radio state.
The 1.4 GHz light curve obtained with the Nasu radio telescope array is shown here. Red triangles indicate non-detections (upper limits of approximately 200 mJy).
We plan to continue daily monitoring to confirm whether Cygnus X-3 remains in this low-flux state.
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.
