Renewed activity of Cygnus X-3 observed with the Nasu telescope array at 1.4 GHz

ATel #17605; K. Tsubono (Univ. Tokyo), K. Asuma (Kawaguchi-Kita High School), K. Niinuma (Yamaguchi Univ.), K. Takefuji (JAXA) and T. Daishido (Waseda Univ.)
on 16 Jan 2026; 12:38 UT
Credential Certification: Kimio Tsubono (tsubono@phys.s.u-tokyo.ac.jp)

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Following the initial report by RATAN-600 (ATel #17600), we independently detected renewed radio emission from Cygnus X-3 with the Nasu telescope array.

Cygnus X-3 is known to exhibit recurrent radio outbursts on timescales of several years. A recent example is the detection of strong radio flaring activity by the RATAN radio monitoring program in July 2024 (ATel #16738).

From mid-November 2025, Cygnus X-3 appears to have entered a quenched hard X-ray state, as indicated by recent Swift/BAT observations in the 15-50 keV band (see https://swift.gsfc.nasa.gov/results/transients/CygX-3/), which show a pronounced suppression of the hard X-ray flux.

An increase in the soft X-ray flux from Cygnus X-3 has been reported in ATel #17585 and suggested as a possible precursor to a forthcoming major radio flare. Such X-ray behavior has historically been observed shortly before strong radio outbursts in this source.

Using the Nasu telescope array, we detected renewed brightening of the radio emission from Cygnus X-3 on 2026 January 16, following approximately 50 days of quiescence. The flux density was measured to be approximately 2.3 Jy at 1.4 GHz (UT 03:30). This renewed radio activity occurs during a prolonged quenched hard X-ray state, a condition historically associated with major radio flaring in Cygnus X-3. The observed behavior may therefore represent the early phase of a larger radio outburst.

We will continue radio monitoring of Cygnus X-3.

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.space