Multi-band radio emission enhancement of the flat spectrum radio quasar OP 313

The significant brightening of the flat spectrum radio quasar OP 313 (BZU J1310+3220, 4FGL J1310.5+3221) was recently been reported in gamma-ray (ATel #17167), near-infrared (ATel #17179) and optical bands (ATel #17173, #17184, #17185) over the past two weeks. This source is included in the RATAN-600 long-term monitoring program, and it has exhibited a consistent upward trend in radio flux density since January 2017.

On 2025 May 8, we measured its flux densities at five frequencies using the RATAN-600 telescope, obtaining the following values (in Jy):

• 4.37 ± 0.6 at 22.3 GHz
• 4.22 ± 0.4 at 14.4 GHz
• 3.93 ± 0.4 at 11.2 GHz
• 3.85 ± 0.3 at 8.2 GHz
• 2.71 ± 0.2 at 4.7 GHz

These measurements indicate that OP 313 is currently in its highest radio emission state observed over the past decade, based on our monitoring data.