Ongoing radio flaring activity of Cyg X-3 at 18.5 GHz with the Medicina Radio Telescope

ATel #18001; E. Egron (INAF-OAC), S. Vercellone, G. Pareschi (INAF-OAB), M. N. Iacolina (ASI), M. Giroletti (INAF-IRA), A. Giuliani (IASF Milano), M. Pilia, A. Pellizzoni (INAF-OAC), M. Tavani (INAF-IAPS) on behalf of a larger collaboration
on 24 Aug 2026; 04:26 UT
Credential Certification: Elise Egron (elise.egron@inaf.it)

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Cyg X-3 has displayed exceptional radio activity throughout 2026, including several giant flares exceeding 10 Jy at 4.7 GHz, as measured with RATAN-600 (Trushkin et al., ATel #17836). The June 2026 flaring episode was also monitored with the 32-m Medicina Radio Telescope. The 18.5-GHz radio emission peaked at approximately 11 Jy on June 10.

We report observations of the microquasar Cyg X-3 with Medicina during its current radio-flaring episode.

The observations were performed at a central frequency of 18.5 GHz using the total-power backend and a bandwidth of 680 MHz. NGC 7027 and 3C 286 were used as flux-density calibrators.

We obtained the following measurements:

2026 August 22 at 02:44 UT: 5.0 +/- 0.3 Jy
2026 August 22 at 17:06 UT: 3.9 +/- 0.2 Jy
2026 August 23 at 01:55 UT: 3.1 +/- 0.1 Jy
2026 August 23 at 03:34 UT: 3.6 +/- 0.1 Jy
2026 August 23 at 17:10 UT: 4.0 +/- 0.1 Jy
2026 August 24 at 01:31 UT: 4.5 +/- 0.1 Jy

During the first 23.2 hours, Cyg X-3 faded from 5.0 to 3.1 Jy. The trend then reversed, and the source brightened steadily to 4.5 Jy over the subsequent 23.6 hours. This renewed rise indicates that the radio-flaring episode remains active.

Medicina monitoring will continue. Multi-wavelength observations of Cyg X-3 are strongly encouraged.